Grounding and Bonding for Electrical Systems
Rewritten so each grounding decision is its own field: electrode resistance target is a range the Engineer sets, GEC and water-bond sizes are derived from the service conductors, and lightning, telecom, cathodic protection and MV cable shields point to the standards that own them.
Showing changes from Rev 7
to Rev 8
in Grounding and Bonding for Electrical Systems.
---
title: Grounding and Bonding for Electrical Systems
category: Electrical
−toc_depth: 3
description: >
− When to use: Grounding and bonding of low-voltage (1000V and below) electrical systems for commercial, institutional, and industrial buildings. Covers the grounding electrode system, grounding electrode conductors, equipment grounding conductors, bonding of metallic systems, separately derived systems, ground bus and ground bars, connections and terminations, and field testing of installed grounding systems.
− Not intended for: Lightning protection systems (see NFPA 780), the telecommunications bonding backbone beyond the point of connection to the building electrical grounding electrode system (see [[sync/telecommunications-bonding]]), medium-voltage substation ground grid design, cathodic protection systems (see [[sync/cathodic-protection]]), or grounding of systems over 1000V.
+ When to use: The grounding and bonding of electrical systems rated 1000 V and below in commercial, institutional, industrial, and water and wastewater facilities: the grounding electrode system and each of its electrodes (concrete-encased, ground ring, rod, pipe and plate, structural metal, metal water pipe, electrolytic), the soil basis the electrode design rests on, the grounding electrode conductor and its routing, the service grounding including the main bonding jumper, the bonding of service raceways and the intersystem bonding termination, the grounding and bonding of every separately derived system, the equipment grounding conductors of feeders and branch circuits and the rules that size them, isolated-ground circuits, the bonding of metallic piping, structural metal and other metal systems, the common bond to the lightning protection, telecommunications and cathodically protected systems, the grounding of direct-current control systems, ground bars, exothermic, compression and mechanical connections, and the field tests that prove the installed system. Every equipment standard in the corpus hands the equipment grounding and bonding of its equipment to this standard.
+ Not intended for: the ground grid of a substation designed under IEEE 80 and the system grounding of circuits above 1000 V, including neutral grounding resistors and reactors, which no SynC standard yet owns; the shield grounding of a medium-voltage cable, whether single-point, multi-point or cross-bonded ([[sync/medium-voltage-cables]]); the strike termination network, its down conductors and its own earth terminations ([[sync/lightning-protection]]); the primary bonding busbar and everything the telecommunications backbone serves downstream of it ([[sync/telecommunications-bonding]]); impressed-current and galvanic corrosion control of buried and submerged steel and iron ([[sync/cathodic-protection]]); the protection technique, wiring method and sealing inside an explosive atmosphere ([[sync/electrical-hazardous-locations]]); the utility point of delivery, the service drop or lateral, the meter and the service disconnecting means ([[sync/electrical-service-entrance]]); the building wire itself, its stranding class and its jacket ([[sync/conductors-and-cables]]); conduit, tubing and their fittings ([[sync/raceways-and-conduit]]) and the tray and its splice plates ([[sync/cable-tray]]); the terminal bar inside a panelboard, switchboard, switchgear or motor control center ([[sync/panelboards]], [[sync/low-voltage-switchboards]], [[sync/low-voltage-switchgear]], [[sync/motor-control-centers]]); the testing organization, its instruments, its safety practice and the compiled report ([[sync/electrical-acceptance-testing]]); label materials and lettering ([[sync/electrical-identification]]); and the piping, ductwork, tanks and structural steel that are bonded, each under its own standard.
---
# Scope {toc}
−## This specification covers the materials, configuration, installation, and field testing of the grounding and bonding systems for low-voltage electrical distribution rated 1000V and below. {note}
+## This standard governs the grounding and bonding of the electrical system as one system: the electrodes in the earth, the conductor that ties the system to them, the single bond between the grounded conductor and the equipment ground at the service and at each separately derived system, the equipment grounding conductor that carries fault current from every enclosure back to that bond, the bonding of the metal piping and structure that could become energized, the common connection to the other grounded systems in the building, the connections that join all of it, and the tests that prove it. {note}
−## Grounding and bonding shall comply with NFPA 70 Article 250 (National Electrical Code).
+## Grounding and bonding do two different jobs. Grounding connects the system to earth so that the voltage to earth is held steady in normal operation and so that lightning and line surges have a path to dissipate. Bonding connects the metal parts to one another and back to the source so that a fault raises enough current to open the overcurrent device. Earth is a poor conductor and never the fault-clearing path; a ground rod at a motor with no bonding conductor back to the panel leaves the frame energized at line voltage while the breaker holds. Most of the requirements in this standard exist because the two jobs are confused in the field. {note}
−## The completed system shall be installed to provide a low-impedance path for fault current, limit voltage imposed by lightning and line surges, stabilize voltage to earth during normal operation, and connect normally non-current-carrying metallic parts of equipment to the source so that overcurrent devices clear ground faults reliably.
+## The equipment standards and this standard divide the work in one way throughout the corpus. The standard for a transformer, a switchboard, a motor, a pump station or a luminaire names what on that equipment is bonded and defers the conductor, its size, its termination and its test to this standard. This standard states the rule once; the equipment standard does not restate it. {note}
−## The Contractor shall treat the requirements of this standard as applying to the service equipment, every separately derived system, every panelboard and distribution assembly, every raceway and cable system, and every piece of utilization equipment on the project.
+## The following are governed elsewhere and are outside this standard: {note}
−## The Contractor shall coordinate raceway and conductor work with [[sync/raceways-and-conduit]] and [[sync/conductors-and-cables]].
+- the ground grid of a substation designed under IEEE 80 and the system grounding of circuits above 1000 V, including neutral grounding resistors and reactors, which no SynC standard yet owns
+- the shield grounding of a medium-voltage cable, whether single-point, multi-point or cross-bonded, under [[sync/medium-voltage-cables]]
+- the strike termination network, its down conductors and its own earth terminations, under [[sync/lightning-protection]]
+- the primary bonding busbar and everything the telecommunications backbone serves downstream of it, under [[sync/telecommunications-bonding]]
+- impressed-current and galvanic corrosion control of buried and submerged steel and iron, under [[sync/cathodic-protection]]
+- the protection technique, wiring method and sealing inside an explosive atmosphere, under [[sync/electrical-hazardous-locations]]
+- the utility point of delivery, the service drop or lateral, the meter and the service disconnecting means, under [[sync/electrical-service-entrance]]
+- the building wire itself, its stranding class and its jacket, under [[sync/conductors-and-cables]]
+- conduit, tubing and their fittings, under [[sync/raceways-and-conduit]], and the tray and its splice plates, under [[sync/cable-tray]]
+- the terminal bar inside a panelboard, switchboard, switchgear or motor control center, under [[sync/panelboards]], [[sync/low-voltage-switchboards]], [[sync/low-voltage-switchgear]] and [[sync/motor-control-centers]]
+- the testing organization, its instruments, its safety practice and the compiled report, under [[sync/electrical-acceptance-testing]]
+- label materials and lettering, under [[sync/electrical-identification]]
+- the piping, ductwork, tanks and structural steel that are bonded, each under its own standard
−## The Contractor shall coordinate service and distribution equipment grounding with [[sync/low-voltage-switchgear]] and [[sync/electrical-rooms]].
+## The grounding and bonding of every electrical system rated 1000 V and below on the project shall comply with this standard.
−## Grounding and bonding is a coordinated system that touches nearly every other electrical scope rather than a single product. {note}
+## The requirements of this standard shall apply to the service equipment, to every separately derived system, to every feeder and branch circuit, to every enclosure, raceway, cable tray, busway and wireway, and to every item of utilization equipment, whether or not the standard governing that item restates them.
−## Grounding is the intentional connection of a system or equipment to earth, and bonding is the connection of metallic parts to each other to establish electrical continuity and conductivity; the two functions shall not be conflated.
+## Where the Contractor and the Engineer of Record disagree whether a metal part is likely to become energized, or whether a connection is accessible, the Engineer of Record shall make the initial determination.
−## Earth itself is not an effective fault-clearing path; the effective ground-fault current path that operates overcurrent devices is created by bonding, not by the connection to earth. {note}
−
−## Where a lightning protection system is installed, it shall be bonded to the building grounding electrode system in accordance with NFPA 780 and NEC 250.106.
−
−## The design and installation of the lightning protection system itself is a separate scope not covered by this standard. {note}
−
# Referenced Standards {toc}
−## Equipment, materials, and installation shall comply with the latest adopted edition of the following standards and codes.
+## Materials and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
+## Where the contract documents, the Authority Having Jurisdiction, or two referenced standards impose conflicting requirements, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
| Standard | Title |
|----------|-------|
−| NFPA 70 | National Electrical Code (Article 250 — Grounding and Bonding) |
+| NFPA 70 | National Electrical Code (Article 250) |
| NFPA 70E | Standard for Electrical Safety in the Workplace |
| NFPA 780 | Standard for the Installation of Lightning Protection Systems |
| UL 467 | Grounding and Bonding Equipment |
−| UL 96 | Lightning Protection Components |
−| UL 869A | Reference Standard for Service Equipment |
−| IEEE 142 | Recommended Practice for Grounding of Industrial and Commercial Power Systems (Green Book) |
−| IEEE 1100 | Recommended Practice for Powering and Grounding Electronic Equipment (Emerald Book) |
| IEEE 81 | Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System |
+| IEEE 142 | Recommended Practice for Grounding of Industrial and Commercial Power Systems |
+| IEEE 3003.2 | Recommended Practice for Equipment Grounding and Bonding in Industrial and Commercial Power Systems |
| IEEE 837 | Standard for Qualifying Permanent Connections Used in Substation Grounding |
+| IEEE 1100 | Recommended Practice for Powering and Grounding Electronic Equipment |
| ANSI/NETA ATS | Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems |
| ANSI/TIA-607 | Generic Telecommunications Bonding and Grounding (Earthing) for Customer Premises |
…3 unchanged lines
| NEMA GR 1 | Grounding Rod Electrodes and Grounding Rod Electrode Couplings |
−## Where the contract documents, the adopted building code, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
−
# Submittals {toc}
## Action Submittals {toc}
−### Contractor shall submit the following for the Engineer's review prior to procurement and installation:
+### The Contractor shall submit the following for review before any grounding electrode is installed or any grounding connection is made:
−- Product data for each grounding and bonding component, including ground rods, ground bars, connectors, exothermic weld molds, compression connectors, and conductors
−- A grounding riser diagram or single-line grounding diagram showing the grounding electrode system, the grounding electrode conductor routing, the location of the main bonding jumper, every separately derived system with its system bonding jumper, and the intersystem bonding termination
−- Conductor sizing calculations for all grounding electrode conductors per NEC 250.66 and all equipment grounding conductors per NEC 250.122 that are not shown on the contract drawings
−- Manufacturer's installation instructions for exothermic and compression connection systems
−- A proposed field test plan describing the ground resistance test method, instruments, and acceptance criteria
+- product data for every grounding and bonding component, including rod electrodes, plate and electrolytic electrodes, ground bars and their insulators, connectors, clamps, bonding bushings and locknuts, exothermic molds and weld metal, compression connectors and the dies that set them, and ground enhancement material
+- a grounding riser diagram showing every electrode, the grounding electrode conductor and its route, the main bonding jumper, every separately derived system with its system bonding jumper and its grounding electrode connection, every ground bar, the intersystem bonding termination, and the connection point of each other grounded system
+- an electrode layout showing the location of each rod, ring, plate and concrete-encased electrode and of each test well
+- a sizing schedule listing each grounding electrode conductor, bonding jumper, system bonding jumper and ground bar bonding conductor with the NFPA 70 table and the conductor size it was sized from
+- the soil resistivity survey, where the datasheet selects the measured basis
```datasheet
−label: Action Submittals Required
+label: Action Submittals
type: checkbox
options:
- "Product data for grounding and bonding components"
− - "Grounding riser / single-line grounding diagram"
− - "Grounding electrode conductor sizing calculations"
− - "Equipment grounding conductor sizing calculations"
− - "Connection system installation instructions"
− - "Field test plan"
−default: "Product data for grounding and bonding components"
+ - "Grounding riser diagram"
+ - "Electrode layout"
+ - "Conductor and jumper sizing schedule"
+ - "Soil resistivity survey"
+default:
+ - "Product data for grounding and bonding components"
+ - "Grounding riser diagram"
+ - "Electrode layout"
+ - "Conductor and jumper sizing schedule"
+constraint: all_of
```
−### Installation shall not proceed on any portion of the grounding system until the corresponding submittals are reviewed and returned.
+### No grounding electrode shall be concealed before the electrode layout covering it has been reviewed and returned.
+### The riser diagram is the document that catches the second neutral-to-ground bond, the transformer with no grounding electrode conductor, and the telecommunications backbone landed on a panel ground bar instead of the electrode system. It is reviewed once, on paper, when each of those costs nothing to move. {note}
+
## Closeout Submittals {toc}
−### Contractor shall provide the following at substantial completion before the grounding system is accepted:
+### The Contractor shall submit the following before the grounding system is accepted:
−- Field test reports for all ground resistance, continuity, and connection-integrity testing, signed by the testing technician
−- As-built grounding riser diagram reflecting the installed routing, electrode locations, and connection points
−- Operation and maintenance data describing inspection intervals and re-test recommendations
−- Warranty documentation for grounding products carrying a manufacturer warranty
+- the field test reports for the electrode resistance, bonding continuity and objectionable current tests, with the method, the instrument, the measured values and the acceptance value for each
+- the record grounding riser diagram and electrode layout, showing the electrodes, conductors, connections and test wells as installed
+- a photographic record of each connection made inaccessible by backfill, concrete or finishes, taken before it was concealed
+- the record of the Authority Having Jurisdiction's inspection of the electrode system before concealment
```datasheet
−label: Required Closeout Submittals
+label: Closeout Submittals
type: checkbox
options:
− - "Signed field test reports (resistance, continuity, connection integrity)"
− - "As-built grounding riser diagram"
− - "Operation and maintenance data"
− - "Warranty documentation"
−default: ["Signed field test reports (resistance, continuity, connection integrity)", "As-built grounding riser diagram", "Operation and maintenance data", "Warranty documentation"]
+ - "Field test reports"
+ - "Record grounding riser diagram and electrode layout"
+ - "Photographic record of concealed connections"
+ - "Inspection record before concealment"
+default:
+ - "Field test reports"
+ - "Record grounding riser diagram and electrode layout"
+ - "Photographic record of concealed connections"
+ - "Inspection record before concealment"
+constraint: all_of
```
+### The record test values are the baseline every later measurement of the electrode system is compared against; a resistance that has doubled in five years is a corroded electrode or a cut conductor, and that is visible only against the first reading. {note}
+
# Quality Assurance {toc}
−## Installer Qualifications {toc}
+## Installer and Connection Qualifications {toc}
−### Grounding and bonding work shall be performed by electricians experienced in the installation of grounding systems and supervised by a licensed electrical contractor.
+### Grounding and bonding work shall be performed under the supervision of a licensed electrical contractor by electricians who have installed grounding electrode systems on not fewer than three completed projects.
−### Personnel making exothermic welded connections shall be trained by the connection-system manufacturer in the specific mold and process being used.
+### Every person who makes an exothermic welded connection shall have been trained by the connection system's manufacturer in the molds and weld metal used on the project and shall make one sample connection of each type used, which shall be sectioned and shown to be free of porosity and slag before that person makes a production connection.
−### Personnel making exothermic welded connections shall demonstrate competency on sample connections before performing production work.
+### Every person who makes a compression connection shall use the die and the tool the connector's listing names for that connector and conductor, and the tool shall be of the type that completes the full crimp before it releases.
−## Connection System Qualification {toc}
+### Connections that are buried, encased in concrete or otherwise inaccessible after installation shall carry the qualification indicated in the datasheet.
−### Permanent grounding connections that are buried, encased in concrete, or otherwise inaccessible after installation shall use a connection method qualified by testing.
+```datasheet
+label: Qualification of Inaccessible Connections
+type: radio
+options:
+ - "Listing to UL 467"
+ - "Listing to UL 467 with qualification to IEEE 837"
+default: "Listing to UL 467"
+```
−### Exothermic welded connections and compression connections used in inaccessible locations should be qualified in accordance with IEEE 837.
+### UL 467 lists a connector for its intended conductors and surfaces and for direct burial or concrete encasement, which is the listing NFPA 70 250.70 requires and the one every building project relies on. IEEE 837 subjects a connection to repeated fault-current, thermal cycling and corrosion exposure that an ordinary mechanical lug does not survive, and is the qualification a substation, a generating station or an Owner's corporate standard asks for where the connection carries fault current from a stiff source and will never be inspected again. {note}
−### Mechanical connections are not permitted in locations that become inaccessible.
+## Listing of Grounding Components {toc}
−### IEEE 837 subjects connections to electrical, thermal, and corrosion testing that an ordinary mechanical lug cannot pass. {note}
+### Every connector, clamp, bonding bushing, bonding locknut, ground bar and rod electrode shall be listed and labeled to UL 467 by a Nationally Recognized Testing Laboratory.
−## Regulatory Inspection {toc}
+### Every connector shall be listed for the conductor material and size range and for the surface it is applied to, and a connector that joins aluminum or copper-clad aluminum to copper shall be listed for that combination.
−### The grounding electrode system, including all electrodes and the grounding electrode conductor connections, shall be available for inspection by the Authority Having Jurisdiction before being concealed by backfill, concrete, or finishes.
+### Every connector in contact with earth or embedded in concrete shall be listed for direct burial or for concrete encasement.
−### The Contractor shall coordinate inspection timing.
+## Inspection Before Concealment {toc}
−### The Contractor shall not conceal any portion of the grounding electrode system until it has been inspected and released.
+### The grounding electrode system, every connection to an electrode, and every conductor to be buried or encased shall be inspected by the Authority Having Jurisdiction and by the Engineer of Record's representative before it is concealed by backfill, concrete or finishes.
−## Listing and Labeling {toc}
+### The Contractor shall give not less than two working days' notice of each inspection and shall not conceal any part of the electrode system before it has been released.
−### All grounding and bonding equipment, including connectors, clamps, bushings, ground bars, and ground rods, shall be listed and labeled to UL 467 by a Nationally Recognized Testing Laboratory.
+### A connection concealed before inspection shall be exposed at the Contractor's cost for inspection and shall be remade where the exposure damaged it.
−### Connectors shall be listed for the specific conductor materials, conductor sizes, and surfaces on which they are used.
+# Soil and Site Conditions {toc}
−### Connectors used in direct contact with earth or concrete shall be additionally listed for direct burial or concrete encasement.
+## Soil Resistivity Design Basis {toc}
−# Environmental and Service Conditions {toc}
+### The electrode system shall be designed to the soil resistivity basis indicated in the datasheet.
−## The performance of a grounding electrode system depends heavily on the soil in which it is installed. {note}
+```datasheet
+label: Soil Resistivity Design Basis
+type: select
+options:
+ - "Measured on site by the four-point method of IEEE 81"
+ - "Taken from the geotechnical report"
+ - "Assumed from regional soil data and confirmed by the electrode resistance test"
+```
−## The Engineer shall establish the design soil resistivity from a site investigation.
+### A four-point survey on the site measures the resistivity at several depths and spacings and is the only basis that predicts the resistance of a ring or a rod field before it is built, at the cost of a survey crew and a day on an undisturbed site; a resistivity taken from the geotechnical report uses a value the geotechnical engineer measured or inferred for corrosion purposes, at one or two locations and often at one depth, which is enough for a building whose electrodes are the footing steel and a pair of rods; an assumed regional value costs nothing and leaves the resistance to be discovered at the test, which suits a project where the code electrodes are expected to meet the target with margin and remedial rods are cheap to add. {note}
−## The Contractor shall report any field condition that differs materially from the design basis.
+### The design soil resistivity shall be the value indicated in the datasheet.
−## Soil resistivity varies by orders of magnitude with moisture content, temperature, mineral content, and compaction. {note}
−
−## Soil Resistivity {toc}
−
```datasheet
−label: Design Soil Resistivity Basis
−type: select
+label: Design Soil Resistivity
+type: range
+unit: Ω·m
+drawing_ref: "the geotechnical report"
options:
− - "Measured on site per IEEE 81 (four-point Wenner method)"
− - "Estimated from geotechnical report"
− - "Assumed pending field verification"
−default: "Estimated from geotechnical report"
+ min: 1
+ max: 10000
+ step: 1
+default: deferred
+constraint: exact
```
−### Where a measured ground resistance value must be achieved and the design soil resistivity is high, the Engineer shall evaluate supplemental measures early in design.
+### Soil resistivity spans four orders of magnitude, from wet clay near 10 Ω·m to dry sand and rock above 1000 Ω·m, and the resistance of a rod is nearly proportional to it. The value fixes how many rods, how long a ring, and whether ground enhancement material is needed, which is why it is settled before the electrodes are priced rather than after the first test fails. {note}
−### Driving electrodes deeper, increasing electrode spacing, extending a ground ring, or adding chemically enhanced or ground-enhancement-material electrodes are all more cost-effective when planned before excavation than when added as remedial work. {note}
+### Where the measured or reported resistivity exceeds the design value by more than 50%, the Contractor shall report the difference to the Engineer of Record before any electrode is installed, and the Engineer of Record shall direct any change to the electrode system in writing.
−## Corrosive Soils {toc}
+## Corrosive Soil and Dissimilar Metals {toc}
−### In soils with low resistivity, high chloride or sulfate content, low pH, or significant dissimilar buried metals, accelerated corrosion of grounding electrodes and connections shall be expected.
+### Every buried electrode shall be of the material indicated in the datasheet.
```datasheet
−label: Soil Corrosivity Classification
−type: select
−options:
− - "Non-corrosive (neutral pH, moderate resistivity)"
− - "Moderately corrosive"
− - "Highly corrosive (low pH, high chloride/sulfate, or aggressive fill)"
−default: "Non-corrosive (neutral pH, moderate resistivity)"
−```
−
−```datasheet
−label: Buried Electrode Material
+label: Electrode Material
type: radio
options:
− - "Copper"
- "Copper-bonded steel"
− - "Stainless steel (corrosive soils)"
+ - "Solid copper"
+ - "Stainless steel"
- "Galvanized steel"
default: "Copper-bonded steel"
```
−### In corrosive soils, the Contractor shall use connection methods and electrode materials selected for corrosion resistance, and shall avoid creating galvanic couples between dissimilar buried metals.
+### A copper-bonded steel rod drives like steel and corrodes like copper, lasts thirty years or more in ordinary soil, and is the rod nearly every building project installs; a solid copper rod bends in driving and is chosen for a plate or a short rod in soil that attacks the steel core at a nick in the bonding; a stainless steel rod resists soil with high chloride or sulfate content, low pH or a cinder fill, and resists the galvanic attack a copper system causes on nearby buried steel, at several times the cost; a galvanized steel rod is the cheapest and is consumed in a few years once the zinc is gone, which is accepted where the Owner's standard is galvanized throughout or the electrode is easy to replace. {note}
−### Galvanized steel electrodes shall not be used where they would be electrically connected through the earth or through buried conductors to copper electrodes.
+### Electrodes of dissimilar metal shall not be installed in one electrode system where they are interconnected through earth by buried bare conductor, unless the Engineer of Record accepts the galvanic exposure in writing.
−### Stainless steel electrodes should be used where the soil is highly corrosive to copper.
+### Where the soil has a pH below 5, a chloride or sulfate content the geotechnical report classes as aggressive, or a cinder, slag or ash fill, every buried connection shall be exothermic welded or a compression connection of the same metal as the conductor, and every buried conductor shall be solid copper or stainless steel.
−### Copper and copper-bonded steel are appropriate for the majority of soil conditions; a copper-to-galvanized galvanic cell consumes the zinc and then the steel. {note}
+### Copper buried in earth and bonded to the building steel, the water service and the reinforcing steel makes every one of them the anode of a galvanic cell with the copper as its cathode. In ordinary soil the current is small and the steel lasts the life of the building; in wet, low-resistivity, low-pH soil it consumes a bare steel pipe or a galvanized rod in a few years, which is the reason a cathodic protection system under [[sync/cathodic-protection]] puts a decoupling device in the bond rather than cutting it. {note}
−## Frost and Seasonal Variation {toc}
+## Frost and Seasonal Moisture {toc}
−### Where the installation is subject to seasonal freezing, electrode design shall account for the increase in soil resistivity that occurs when soil freezes.
+### Where [[parameter: frost-depth]] exceeds the ground ring burial depth indicated in the datasheet, the resistance target shall be met by rod electrodes extending below the frost depth and not by the ring alone.
−### Driven electrodes shall extend below the local frost depth so that the lower portion remains in unfrozen, conductive soil year-round.
+### Rod electrodes shall be driven so that the full length of the rod below its top is in contact with soil and the lower end of each rod is not less than 2 ft below [[parameter: frost-depth]].
−### Frost depth shall be [[drawing: as indicated on the civil drawings or determined from the local building code]].
+### Frozen soil has a resistivity ten to a hundred times that of the same soil thawed, and an electrode system that meets its target in October and fails in February is one whose electrodes all lie in the frost zone. The rod that reaches permanently moist soil below the frost line carries the system through the winter. {note}
# Grounding Electrode System {toc}
−## The grounding electrode system is the set of electrodes that connect the electrical system to earth. {note}
+## Electrodes Relied On {toc}
−## All grounding electrodes present at a building or structure shall be bonded together to form a single grounding electrode system, in accordance with NEC 250.50.
+### Every grounding electrode present at the building or structure that NFPA 70 250.52(A) recognizes shall be bonded together to form one grounding electrode system, in accordance with NFPA 70 250.50, whether or not it is selected in the datasheet.
−## A common field error is to install a driven rod and ignore the concrete-encased electrode, the metal water pipe, or the building steel that are also present; all qualifying electrodes must be bonded together.
+### The electrodes the design relies on to meet the resistance target shall be as indicated in the datasheet.
−## Required Electrodes {toc}
−
```datasheet
−label: Grounding Electrodes Present and Bonded
+label: Grounding Electrodes Relied On
type: checkbox
options:
− - "Concrete-encased electrode (Ufer)"
+ - "Concrete-encased electrode"
- "Ground ring"
+ - "Rod electrodes"
+ - "Pipe electrodes"
+ - "Plate electrodes"
+ - "Structural metal in direct contact with earth"
- "Metal underground water pipe"
− - "Driven rod, pipe, or plate electrode"
− - "Metal in-ground support structure (building steel)"
− - "Other listed electrode"
−default: "Concrete-encased electrode (Ufer)"
+ - "Electrolytic electrodes"
+default:
+ - "Concrete-encased electrode"
+ - "Rod electrodes"
+constraint: all_of
```
−### Every electrode listed that exists at the building shall be bonded into the grounding electrode system.
+### The selection records which electrodes the design counts on; it never relieves the obligation to bond every qualifying electrode that exists. The common field error is to drive two rods and ignore the footing steel, the building columns and the metal water service, each of which NFPA 70 250.50 requires to be bonded and each of which lowers the resistance more than the rods do. {note}
−### The Contractor shall bond any qualifying electrode that is present, whether shown or not; the selection records which electrodes the project relies on but does not relieve this obligation.
+### Where no electrode of the types NFPA 70 250.52(A)(1) through (A)(7) exists at a building or structure, one or more of the electrodes of 250.52(A)(4) through (A)(8) shall be installed, in accordance with NFPA 70 250.50.
−### Concrete-encased electrode {toc}
+### A metal underground gas piping system, an aluminum electrode, and the structures and reinforcing steel of a swimming pool shall not be used as grounding electrodes, in accordance with NFPA 70 250.52(B).
−#### Where a building has a concrete foundation or footing in direct contact with earth, a concrete-encased electrode shall be provided in accordance with NEC 250.52(A)(3).
+## Concrete-Encased Electrode {toc}
−#### The concrete-encased electrode shall consist of at least 20 ft of either bare copper conductor not smaller than 4 AWG, or one or more bare zinc-coated or uncoated steel reinforcing bars not smaller than 1/2 in. diameter.
+### Where a footing or foundation in direct contact with earth is poured on the project, a concrete-encased electrode shall be provided in it, in accordance with NFPA 70 250.52(A)(3), and shall be of the form indicated in the datasheet.
−#### The concrete-encased electrode shall be encased by at least 2 in. of concrete and located within and near the bottom of a foundation or footing that is in direct contact with the earth.
+```datasheet
+label: Concrete-Encased Electrode Conductor
+type: radio
+options:
+ - "Bare copper conductor in the footing"
+ - "Reinforcing steel of the footing"
+```
−#### The Contractor shall coordinate the installation of the concrete-encased electrode connection point with the structural and concrete trades so that a connection tail extends out of the foundation before concrete is placed.
+### A bare copper conductor laid in the footing is a dedicated electrode the electrical trade installs and inspects itself, with a tail that leaves the concrete wherever the design wants it, at the cost of 20 ft or more of 4 AWG copper and a trip to the site before the pour; the reinforcing steel is already in the footing, forms a far longer electrode than the copper conductor, and costs only the listed connector and the stub, at the cost of depending on the reinforcing trade to tie the bars electrically continuous and to leave the stub where the electrical trade needs it. {note}
−#### The concrete-encased electrode is the most effective and most durable electrode available on most projects because the concrete itself behaves as a large, moisture-retaining, conductive mass, and retrofitting one after the pour is not feasible. {note}
+### Where the bare copper conductor form is selected, the electrode shall consist of not less than 20 ft of bare copper conductor not smaller than 4 AWG, encased by not less than 2 in. of concrete and located near the bottom of a footing or foundation that is in direct contact with earth.
−### Ground ring {toc}
+### Where the reinforcing steel form is selected, the electrode shall consist of not less than 20 ft of bare, zinc-coated or electrically conductive coated reinforcing bar not smaller than 1/2 in. in diameter, made electrically continuous by the usual steel tie wires or by exothermic welding or listed connectors, located as the copper form is located, and connected to the grounding electrode conductor through a listed connector or a bar that extends out of the concrete.
+### The connection to a concrete-encased electrode shall be made to a conductor or bar that extends out of the concrete, or by a listed connector installed before the pour, and no connection shall be made by chipping into cured concrete.
+
+### The Contractor shall coordinate the location of the electrode and the point where its tail or stub leaves the concrete with the concrete and reinforcing trades before reinforcement is placed, and shall protect the tail from the pour until it is terminated.
+
+### Concrete below grade draws moisture from the soil and holds it, so a footing electrode has a lower and more stable resistance than any rod field a building project would install, and it costs almost nothing when it is placed before the pour. It cannot be added afterward, which is why its installation is a hold point and why NFPA 70 250.50 requires it wherever a footing is poured. {note}
+
+## Ground Ring {toc}
+
+### Where a ground ring is selected, it shall encircle the building or structure, shall be in direct contact with earth, shall consist of not less than 20 ft of bare copper conductor of the size indicated in the datasheet, and shall be buried at not less than the depth indicated in the datasheet, in accordance with NFPA 70 250.52(A)(4) and 250.53(F).
+
```datasheet
−label: Ground Ring
−type: radio
+label: Ground Ring Conductor Size
+type: select
+unit: AWG/kcmil
options:
− - "Not required"
− - "Provided around the building or structure"
−default: "Not required"
+ - "2 AWG"
+ - "1/0 AWG"
+ - "2/0 AWG"
+ - "4/0 AWG"
+ - "250 kcmil"
+ - "500 kcmil"
```
−#### Where a ground ring is provided, it shall encircle the building or structure, be in direct contact with earth, and consist of at least 20 ft of bare copper conductor not smaller than 2 AWG, in accordance with NEC 250.52(A)(4).
+```datasheet
+label: Ground Ring Burial Depth
+type: range
+unit: in
+options:
+ min: 30
+ max: 60
+ setpoints: [30, 36, 42, 48, 60]
+default: 30
+constraint: min
+```
−#### A ground ring shall be buried at least 30 in. below grade per NEC 250.53(F).
+### A ring of 2 AWG is the smallest NFPA 70 permits and is enough where the ring exists to tie rods together and give the service a low-resistance electrode; a ring of 1/0 through 4/0 survives mechanical damage during later excavation and corrosion over the life of the building and is the size a data center, a communications site or a lightning-exposed structure specifies; 250 kcmil and 500 kcmil rings are installed where the ring carries the fault current of a large generator plant or a substation on the same site and the ring is sized for that current. A ring at 30 in. meets the code minimum; a deeper ring lies below the frost line and the dry surface layer and reads a lower and more constant resistance, at the cost of a deeper trench and a hazard to other utilities in the same corridor. {note}
−#### Ground rings are commonly specified for buildings with sensitive electronic systems, data centers, and structures where a low and stable ground resistance is required. {note}
+### The ring shall be installed not less than 2 ft from the foundation wall or footing, and rod electrodes bonded to the ring shall be connected to it by exothermic welding or by listed irreversible compression connectors.
−### Driven rod, pipe, and plate electrodes {toc}
+### The ring shall be installed in one continuous length wherever practicable, and a splice in the ring shall be exothermic welded or a listed irreversible compression connection.
+## Rod, Pipe, and Plate Electrodes {toc}
+
+### Rod electrodes shall conform to NEMA GR 1, shall be listed to UL 467, and shall be of the length and diameter indicated in the datasheet.
+
```datasheet
−label: Driven Rod Length
−type: select
+label: Rod Electrode Length
+type: range
unit: ft
options:
− - "8 ft (single section)"
− - "10 ft (single section)"
− - "Sectional rod, coupled to required depth"
−default: "10 ft (single section)"
+ min: 8
+ max: 40
+ setpoints: [8, 10, 12, 16, 20, 30, 40]
+default: 10
+constraint: min
```
```datasheet
−label: Driven Rod Diameter
−type: radio
+label: Rod Electrode Diameter
+type: range
unit: in
options:
− - "5/8 in"
− - "3/4 in"
−default: "3/4 in"
+ min: 0.5
+ max: 1
+ setpoints: [0.5, 0.625, 0.75, 1]
+default: 0.75
+constraint: min
```
−#### Rod and pipe electrodes shall be not less than 8 ft in length and shall be installed so that at least 8 ft of length is in contact with the soil, in accordance with NEC 250.53(G).
+### An 8 ft rod is the shortest NFPA 70 250.52(A)(5) permits and the rod a residential service drives; a 10 ft rod of 3/4 in. diameter is the rod commercial projects specify, because the extra length reaches past the dry surface layer and the larger diameter resists bending in driving and couples reliably when sections are added; rods of 16 ft and longer are sectional rods coupled as they are driven, used where the resistivity survey shows a conductive layer at depth and a long rod reaches it for less than a field of short ones. A 1/2 in. rod is permitted only where it is listed; a 1 in. rod is specified for driving into dense soil or for a design life beyond thirty years in corrosive soil. {note}
−#### Rod electrodes shall be not less than 5/8 in. in diameter unless listed.
+### Rod and pipe electrodes shall be installed so that not less than 8 ft of length is in contact with the soil and shall be driven to a depth of not less than 8 ft, except that where rock is encountered the electrode shall be driven at an angle not exceeding 45° from vertical or buried in a trench not less than 30 in. deep, in accordance with NFPA 70 250.53(G).
−#### Where rock bottom is encountered, the electrode shall be driven at an oblique angle not exceeding 45 degrees from vertical, or buried in a trench at least 30 in. deep, as permitted by NEC 250.53(G).
+### The number of rod electrodes installed shall follow the basis indicated in the datasheet.
−#### A single rod, pipe, or plate electrode that does not have a resistance to earth of 25 Ω or less shall be supplemented by one additional electrode, in accordance with NEC 250.53(A)(2).
+```datasheet
+label: Rod Electrode Count Basis
+type: radio
+options:
+ - "Two rods installed without measuring the first"
+ - "Single rod, supplemented only where its measured resistance exceeds 25 Ω"
+default: "Two rods installed without measuring the first"
+```
−#### Where two rods are used, they shall be spaced at least 6 ft apart.
+### NFPA 70 250.53(A)(2) permits a single rod whose resistance to earth is 25 Ω or less and requires a second where it is not. Installing two rods without the measurement costs one rod and saves the test visit, and is what nearly every commercial project does; measuring the first rod and stopping there is the arrangement of a small structure in conductive soil where the rod is the only electrode and the single test is cheaper than the second rod. {note}
−#### Spacing of at least one rod length is recommended because closely spaced rods share the same volume of soil and add little. {note}
+### Rod electrodes shall be spaced not less than 6 ft apart and not less than the length of the longer rod, and where more than two rods are installed they shall be arranged in a line or around the structure so that no rod lies within the length of another.
−#### The 25-Ω threshold is a code minimum, not a performance target; the project value shall be taken from the testing requirements of this standard.
+### Two rods driven a foot apart share the same shell of soil and read little better than one; at a spacing equal to the rod length each works in its own soil and the pair reads close to half of one rod's resistance, which is where the spacing rule comes from. {note}
−#### A 3/4 in. rod is recommended over the 5/8 in. minimum because the larger diameter resists bending during driving, couples more reliably for sectional rods, and provides greater corrosion margin over the life of the installation. {note}
+### Pipe electrodes shall be not smaller than metric designator 21 (trade size 3/4), galvanized or otherwise coated against corrosion, and installed as rod electrodes are installed.
−### Metal underground water pipe {toc}
+### Plate electrodes shall expose not less than 2 ft² of surface to the soil, shall be not less than 0.06 in. thick where of bare or electrically conductive coated iron or steel and not less than 0.06 in. thick where of solid uncoated nonferrous metal, and shall be buried not less than 30 in. below grade, in accordance with NFPA 70 250.52(A)(7) and 250.53(H).
−#### A metal underground water pipe in direct contact with earth for 10 ft or more shall be used as a grounding electrode where present, in accordance with NEC 250.52(A)(1).
+## Structural Metal and Metal Water Pipe Electrodes {toc}
−#### A metal water pipe electrode shall always be supplemented by at least one additional electrode.
+### A metal in-ground support structure in direct contact with earth for 10 ft or more, with or without concrete encasement, shall be used as a grounding electrode, in accordance with NFPA 70 250.52(A)(2).
−#### The bonding connection to the water pipe shall be made within the first 5 ft of the pipe's entrance into the building.
+### A metal underground water pipe in direct contact with earth for 10 ft or more shall be used as a grounding electrode and shall be supplemented by at least one other electrode of a type NFPA 70 250.52(A)(2) through (A)(8) recognizes, in accordance with NFPA 70 250.52(A)(1) and 250.53(D)(2).
−#### Any insulating fitting or water meter shall be bypassed with a bonding jumper sized per NEC 250.53(D).
+### The connection to a metal water pipe electrode shall be made within the first 5 ft of the pipe's entrance into the building, and every water meter, filter, dielectric fitting or other removable device in that length shall be bypassed by a bonding jumper sized as the grounding electrode conductor is sized, in accordance with NFPA 70 250.53(D)(1) and 250.68(B).
−#### Water utilities increasingly insert nonmetallic pipe sections and dielectric fittings that can interrupt the water-pipe electrode without notice. {note}
+### A water utility replaces a metal service with plastic without telling the building, and a plumber installs a dielectric union at the meter. Either one removes the water-pipe electrode, which is why NFPA 70 never lets it stand alone and why the connection and the jumper around the meter are made where they can be seen. {note}
−## Electrode Connection Accessibility {toc}
+## Ground Enhancement and Electrolytic Electrodes {toc}
−### The connection of the grounding electrode conductor to a grounding electrode shall be accessible, except that connections to concrete-encased electrodes, driven rods, and other buried or encased electrodes are permitted to be inaccessible, in accordance with NEC 250.68(A).
+### Ground enhancement material shall be used as indicated in the datasheet.
−### Where a connection to an electrode will be buried or encased, the connection method shall be exothermic welding or a listed irreversible compression connector.
+```datasheet
+label: Ground Enhancement Material
+type: radio
+options:
+ - "Not used"
+ - "Applied at every rod and plate electrode"
+ - "Applied as a remedial measure where the measured resistance exceeds the target"
+default: "Not used"
+```
−### Mechanical lugs and bolted clamps shall not be buried or encased.
+### Ground enhancement material is a conductive, hygroscopic backfill placed around an electrode to lower the contact resistance between the metal and a poor soil. It is unnecessary where the soil resistivity is low and the footing steel and rods meet the target on their own, which is most buildings; applying it at every rod is the design of a site on sand, gravel or rock where the survey shows the rods alone cannot reach the target; applying it as a remedial measure lets the project install the code electrodes first and spend on enhancement only at the electrodes that need it, at the cost of a second mobilization after the test. {note}
+### Where ground enhancement material is used, it shall be a listed, permanent, non-corrosive material with a resistivity not exceeding 0.2 Ω·m, shall be placed around the electrode in an augered hole or a trench in accordance with the material manufacturer's instructions, and shall not be a salt, a chemical that leaches into the soil, or bentonite alone.
+
+### Where electrolytic electrodes are selected, each shall be a listed copper tube electrode charged with a hygroscopic salt that leaches through breather holes into the surrounding soil, installed vertically or horizontally in ground enhancement material in accordance with its listing, with its cap accessible for recharging in a test well.
+
+### Bentonite holds water while the ground stays wet and shrinks away from the electrode when the soil dries, and a salt backfill lowers the resistance for a season and then corrodes the electrode it surrounds. The listed enhancement materials set permanently around the electrode and do neither, which is why the clause names what the material is not. {note}
+
+## Auxiliary Electrodes at Outdoor Equipment {toc}
+
+### An electrode installed at a light pole, a photovoltaic array, a pedestal, a pad-mounted enclosure or other outdoor equipment shall be an auxiliary electrode in accordance with NFPA 70 250.54, shall be bonded to the equipment grounding conductor of the circuit serving the equipment, and shall not be used in place of that conductor.
+
+### An auxiliary electrode is exempt from the resistance target and the bonding rules of this standard, and the equipment grounding conductor to the equipment shall be sized and installed as though the electrode did not exist.
+
+### Where a separate building or structure is supplied by a feeder or branch circuit, a grounding electrode system shall be installed at that building or structure and connected to the equipment grounding conductor of the feeder, in accordance with NFPA 70 250.32, and the grounded conductor shall not be connected to the electrode system or to the equipment ground at the separate building.
+
+### A rod at a light pole gives lightning on the pole a path to earth that does not run through the building; it does nothing for a fault on the pole circuit, whose current must still flow back to the source on the equipment grounding conductor to open the breaker. The two are confused often enough that NFPA 70 250.54 says so in words. {note}
+
+## Resistance to Earth Target {toc}
+
+### The resistance to earth of the grounding electrode system, measured as the Testing article requires, shall not exceed the value indicated in the datasheet.
+
+```datasheet
+label: Resistance to Earth of the Grounding Electrode System
+type: range
+unit: Ω
+options:
+ min: 1
+ max: 25
+ setpoints: [1, 2, 3, 5, 10, 15, 25]
+constraint: max
+```
+
+### NFPA 70 names 25 Ω only as the threshold at which a single rod must be supplemented, and places no resistance requirement on the electrode system as a whole. The value a project selects is a design decision, not a code reading: 25 Ω accepts the code electrodes as installed and suits a structure in conductive soil with no sensitive loads; 5 Ω is the value most commercial and institutional projects write, gives margin against seasonal drying, and is reached by the footing steel and a few rods in ordinary soil; 1 to 3 Ω is the value a data center, a communications site, a hospital or a facility with a lightning protection system specifies under IEEE 1100 and the equipment makers' installation requirements, and in high-resistivity soil it is reached only with a ring, long rods or enhancement material designed from a resistivity survey. The lower the value, the more the electrode system costs, and below the point where the system meets NFPA 70 the lower value buys surge performance and a stable reference for electronics, not fault clearing. {note}
+
+### Where the datasheet states no value, the supplementation rule of NFPA 70 250.53(A)(2) shall be the only resistance requirement on the electrode system.
+
+### Where the measured resistance exceeds the value in the datasheet, the Contractor shall add rod electrodes, extend the ring or apply ground enhancement material, as the Engineer of Record directs, and shall retest, and the cost of the first two additional electrodes shall be borne by the Contractor.
+
+### Where the value in the datasheet is not reached after the additional electrodes the Engineer of Record directs have been installed, the Engineer of Record shall set the accepted value in writing, and the additional electrodes beyond the first two shall be paid for as a change to the Work.
+
# Grounding Electrode Conductor {toc}
−## The grounding electrode conductor connects the grounded conductor of the service or the equipment grounding conductor, or both, to the grounding electrode system. {note}
−## It is the conductor that establishes the system's reference to earth. {note}
+## Conductor Material {toc}
−## Material and Type {toc}
+### The grounding electrode conductor shall be of the material indicated in the datasheet.
```datasheet
…2 unchanged lines
options:
- "Copper"
− - "Aluminum or copper-clad aluminum"
+ - "Aluminum"
+ - "Copper-clad aluminum"
default: "Copper"
```
−```datasheet
−label: Grounding Electrode Conductor Type
−type: radio
−options:
− - "Solid"
− - "Stranded"
−default: "Stranded"
−```
+### A copper grounding electrode conductor runs in earth, in concrete and outdoors to the electrode without restriction and is the conductor nearly every project installs, because the conductor nearly always ends at an electrode in or near the earth; aluminum and copper-clad aluminum cost less and are chosen for a long run inside a building to a structural steel electrode, and each is barred by NFPA 70 250.64(A) from contact with masonry or earth, from corrosive conditions and from outdoor runs within 18 in. of earth, so that the last length to a buried electrode is copper in any case. {note}
−### Copper shall be used for the grounding electrode conductor in most applications.
+### Where aluminum or copper-clad aluminum is selected, the conductor shall not be installed in direct contact with masonry or earth, in a corrosive location, or outdoors within 18 in. of earth, and the final length to any electrode in earth or concrete shall be copper joined to the aluminum through a listed connector in accordance with NFPA 70 250.64(A).
−### Aluminum or copper-clad aluminum grounding electrode conductors shall not be used where in direct contact with masonry or earth, where subject to corrosive conditions, or installed outdoors within 18 in. of earth, in accordance with NEC 250.64(A).
+### Copper grounding electrode conductors shall be soft-drawn copper conforming to ASTM B3, stranded in accordance with ASTM B8 where larger than 8 AWG, and bare or insulated as the Continuity, Routing, and Protection article requires.
−### Because grounding electrode conductors so frequently run to buried or near-earth electrodes, copper is the practical default. {note}
+## Conductor Size {toc}
−## Grounding Electrode Conductor Sizing {toc}
+### The grounding electrode conductor at the service shall be sized in accordance with NFPA 70 Table 250.66 from the largest ungrounded service-entrance conductor or the equivalent area of parallel conductors, and shall be the size indicated in the datasheet.
```datasheet
label: Grounding Electrode Conductor Size
type: select
unit: AWG/kcmil
−drawing_ref: true
+derived: "the largest ungrounded service-entrance conductor, per NFPA 70 Table 250.66"
options:
- "8 AWG"
…5 unchanged lines
- "3/0 AWG"
- "250 kcmil"
− - "350 kcmil"
−default: deferred
+default: derived
```
−### The grounding electrode conductor shall be sized in accordance with NEC Table 250.66, based on the size of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors.
+### The portion of the grounding electrode conductor that is the sole connection to a rod, pipe or plate electrode is not required to be larger than 6 AWG copper; the portion that is the sole connection to a concrete-encased electrode is not required to be larger than 4 AWG copper; and the portion that is the sole connection to a ground ring is not required to be larger than the ring conductor, in accordance with NFPA 70 250.66(A) through (C).
−### The Contractor shall not size the grounding electrode conductor from the equipment grounding conductor table.
+### Where one conductor serves more than one electrode, the full size from NFPA 70 Table 250.66 shall apply to every portion of the conductor that serves more than one of them.
−### The portion of the grounding electrode conductor that is the sole connection to a concrete-encased electrode is not required to be larger than 4 AWG copper, per NEC 250.66.
+### The grounding electrode conductor shall not be sized from NFPA 70 Table 250.122.
−### The portion that is the sole connection to a ground ring is not required to be larger than the ring conductor, per NEC 250.66.
+### Table 250.66 sizes the conductor from the service conductors, because the service has no overcurrent device ahead of it and the conductor must survive whatever the utility can deliver; Table 250.122 sizes an equipment grounding conductor from the breaker that protects the circuit. Reading one table for the other is the most common sizing error in a grounding submittal and produces a conductor a size or two wrong in either direction. {note}
−### The portion that is the sole connection to a rod, pipe, or plate electrode is not required to be larger than 6 AWG copper, per NEC 250.66.
+## Continuity, Routing, and Protection {toc}
−### Where one continuous conductor serves multiple electrodes, the full Table 250.66 size applies to the common portion.
+### The grounding electrode conductor shall be installed in one continuous length without splice or joint from the point of connection at the service or derived system to the electrode, except that it may be spliced by exothermic welding, by a listed irreversible compression connector, or at a ground bar, in accordance with NFPA 70 250.64(C).
−### The grounding electrode conductor size shall be [[drawing: as indicated on the grounding riser diagram]] and verified against NEC Table 250.66.
+### The grounding electrode conductor shall be routed as directly as the structure permits, with no bend sharper than the conductor manufacturer permits, and shall be secured to the surface it follows at intervals not exceeding 5 ft.
−### Confusing Table 250.66 with Table 250.122 is one of the most common grounding errors and produces a conductor of the wrong size. {note}
+### The grounding electrode conductor shall be installed in the raceway indicated in the datasheet, and a conductor smaller than 6 AWG, and any conductor exposed to physical damage, shall be installed in rigid metal conduit, intermediate metal conduit, rigid PVC conduit, electrical metallic tubing or cable armor in accordance with NFPA 70 250.64(B) whatever the datasheet selects.
−## Continuity and Splices {toc}
+```datasheet
+label: Grounding Electrode Conductor Raceway
+type: radio
+options:
+ - "None, conductor secured to the surface where 6 AWG or larger"
+ - "Rigid PVC conduit"
+ - "Ferrous metal raceway bonded to the conductor at each end"
+```
−### The grounding electrode conductor shall be installed in one continuous length without a splice or joint, except where spliced by irreversible compression connectors listed for the purpose, by exothermic welding, or where busbars are connected together, in accordance with NEC 250.64(C).
+### A bare conductor secured to the wall is the simplest installation, is permitted for 6 AWG and larger where it is not exposed to damage, and is what an electrical room with no traffic gets; rigid PVC conduit protects the conductor without the magnetic effect of a steel raceway and is the raceway most projects use where the conductor crosses a floor, a loading area or a mechanical room; a ferrous raceway gives the strongest protection and is chosen where the conductor runs in a space with vehicle or cart traffic, at the cost of bonding the raceway to the conductor at both ends, which NFPA 70 250.64(E) requires and which the field misses more often than any other grounding detail. {note}
−### Bolted, screwed, or otherwise removable splices in the grounding electrode conductor are not permitted.
+### Where a ferrous metal raceway or enclosure encloses the grounding electrode conductor, the raceway shall be electrically continuous from the enclosure to the electrode and shall be bonded to the conductor at each end and at every intermediate enclosure by a bonding jumper of the same size as the conductor, in accordance with NFPA 70 250.64(E).
−### The intent is that the path to the grounding electrode system cannot be casually opened. {note}
+### A steel conduit around a conductor carrying surge or fault current acts as a choke that raises the impedance of the path many times over, because the current is alternating and the steel is magnetic. Bonding the conduit to the conductor at both ends puts the conduit in parallel with the conductor and cancels the effect; leaving it unbonded leaves the electrode system connected through a choke. {note}
−## Physical Protection {toc}
+### An insulated grounding electrode conductor shall be green, green with a yellow stripe, or bare, and where a bare conductor is installed in a raceway with other conductors it shall be identified at each termination as the grounding electrode conductor.
−### A grounding electrode conductor of 6 AWG copper or larger that is free from exposure to physical damage is permitted to run along the surface of the building without metal covering, in accordance with NEC 250.64(B).
+# Service Grounding and Main Bonding Jumper {toc}
−### Conductors smaller than 6 AWG, and any conductor exposed to physical damage, shall be protected in rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, electrical metallic tubing, or cable armor.
+## Main Bonding Jumper {toc}
−### Where a grounding electrode conductor is installed in a ferrous metal raceway, the raceway shall be electrically continuous from the cabinet or enclosure to the electrode, and the conductor shall be bonded to the raceway at both ends, in accordance with NEC 250.64(E).
+### The grounded service conductor, the equipment grounding conductors and the service equipment enclosure shall be connected together by one main bonding jumper at the service disconnecting means, in accordance with NFPA 70 250.24(B) and 250.28, and the grounding electrode conductor shall be connected to the grounded conductor at the same point.
−### A ferrous raceway around a grounding conductor acts as a choke and increases the impedance of the path; bonding both ends cancels this effect, and this requirement is frequently missed and shall be specifically verified during inspection. {note}
+### Where the service has more than one disconnecting means in separate enclosures, a main bonding jumper shall be installed in each, and the grounded conductor shall be run to each in accordance with NFPA 70 250.24(C).
−# Equipment Grounding Conductor {toc}
+### The main bonding jumper shall be the bus, strap or screw furnished with the listed service equipment and identified by its manufacturer for that purpose, or, where the equipment furnishes none, a wire-type jumper of copper or aluminum sized in accordance with NFPA 70 250.28(D).
−## The equipment grounding conductor bonds the normally non-current-carrying metal parts of equipment, raceways, and enclosures together and back to the source. {note}
−## It is the conductor that carries ground-fault current back to the source so that the overcurrent device operates; the equipment grounding conductor, not the earth, is the effective ground-fault current path. {note}
+### A wire-type main bonding jumper shall be not smaller than the size NFPA 70 Table 250.102(C)(1) gives for the service-entrance conductors, and where the service-entrance conductors exceed 1100 kcmil copper or 1750 kcmil aluminum, not smaller than 12.5% of the area of the largest ungrounded conductor.
−## Type of Equipment Grounding Conductor {toc}
+### A bonding screw furnished as the main bonding jumper shall be green, shall be visible after installation, and shall be installed only in the service equipment, and the screw or strap furnished in every panelboard downstream of the service shall be removed and discarded.
−```datasheet
−label: Equipment Grounding Conductor Type
−type: radio
−drawing_ref: true
−options:
− - "Insulated or covered copper conductor in every raceway and cable"
− - "Metallic raceway serving as the equipment grounding conductor"
−default: "Insulated or covered copper conductor in every raceway and cable"
−```
+### The main bonding jumper is the single point at which the neutral and the equipment ground are joined for a service, and every fault anywhere downstream returns to the source through it. It is one of the few connections in the building whose absence is invisible until a fault, when the breaker does not trip and every enclosure on the system rises to line voltage. {note}
−```datasheet
−label: Equipment Grounding Conductor Material
−type: radio
−options:
− - "Copper"
− - "Aluminum or copper-clad aluminum"
−default: "Copper"
−```
+## Bonding of Service Raceways and Enclosures {toc}
−```datasheet
−label: Wire-Type Equipment Grounding Conductor Insulation Color
−type: radio
−options:
− - "Green"
− - "Green with yellow stripe"
− - "Bare"
−default: "Green"
−```
+### Every metal raceway, cable armor, auxiliary gutter, meter enclosure and other enclosure that contains service conductors shall be bonded together and to the service equipment by one of the means NFPA 70 250.92(B) recognizes: a threaded coupling or hub made up wrench-tight, a bonding-type locknut or bushing, or a bonding jumper installed around a knockout.
−### NEC 250.118 recognizes several wiring methods as equipment grounding conductors, including rigid metal conduit, intermediate metal conduit, and electrical metallic tubing.
+### Standard locknuts and bushings shall not be relied on as the bonding means for any enclosure containing service conductors, and a bonding jumper shall be installed around every concentric, eccentric or oversized knockout in the service path.
−### A wire-type equipment grounding conductor installed in every raceway is recommended for all feeders and for branch circuits serving sensitive, life-safety, or critical loads.
+### Supply-side bonding jumpers shall be sized in accordance with NFPA 70 250.102(C) from the largest ungrounded supply conductor in the raceway or enclosure they bond.
−### Where a metallic raceway is relied upon as the sole equipment grounding conductor, every connection in the raceway run shall be made wrench-tight.
+### A service raceway carries current from a fault on the service conductors with no overcurrent device ahead of it except the utility's, which can take seconds to clear. A single locknut cannot be assured to carry that current, which is why the bonding of the service path is a separate and stricter requirement than the bonding of the raceways downstream. {note}
−### Insulated equipment grounding conductors of 6 AWG and smaller shall be identified by a continuous green color or green with yellow stripes, in accordance with NEC 250.119.
+## Neutral Isolation Downstream of the Service {toc}
−### Conductors larger than 6 AWG are permitted to be re-identified green at terminations.
+### The grounded conductor shall not be connected to the equipment grounding conductors, to an enclosure or to a ground bar at any point on the load side of the service disconnecting means, except as NFPA 70 250.142(B) permits, and the neutral bus of every panelboard, switchboard and transfer switch downstream of the service shall be insulated from its enclosure.
−### A wire-type equipment grounding conductor provides a continuous, predictable path that does not depend on the integrity of every coupling, connector, and locknut. {note}
+### Before energization, the Contractor shall verify at every downstream panelboard and distribution assembly that the neutral bus is isolated from the enclosure and that no bonding screw or strap remains in place, and shall record the verification on the continuity test report.
−## Equipment Grounding Conductor Sizing {toc}
+### The grounding and bonding system shall be arranged so that no current flows on an equipment grounding conductor, a bonding jumper, a raceway or the structure under normal operation, in accordance with NFPA 70 250.6, and where such current is found it shall be removed by correcting the wiring error and never by interrupting a grounding or bonding connection.
+### A second neutral-to-ground bond at a downstream panel puts the building's neutral current onto every parallel path between that panel and the service: the conduit, the building steel, the water pipe and the equipment grounding conductors. The result is a current on the ground system that heats connections, corrodes the pipe at every joint, and couples noise into every signal cable in the building. The cure is to find the bond and remove it; opening a ground to stop the current leaves the fault path open too. {note}
+
+## Intersystem Bonding Termination {toc}
+
+### An intersystem bonding termination shall be provided at the service equipment of each building and at the disconnecting means of each separate building or structure supplied by a feeder, in accordance with NFPA 70 250.94, and shall be of the form indicated in the datasheet.
+
```datasheet
−label: Equipment Grounding Conductor Sizing Source
+label: Intersystem Bonding Termination
type: radio
options:
− - "Indicated on drawings for each feeder"
− - "Per NEC Table 250.122 by overcurrent device rating"
−default: "Per NEC Table 250.122 by overcurrent device rating"
+ - "Listed external termination device at the service equipment"
+ - "Terminals integral to the meter or service enclosure"
+ - "Separate bus bar near the service equipment"
+default: "Listed external termination device at the service equipment"
```
−### The equipment grounding conductor shall be sized in accordance with NEC Table 250.122, based on the rating of the overcurrent device protecting the circuit conductors.
+### The listed external device mounts on the outside of the service equipment or on the grounding electrode conductor, offers its terminals without opening a cover, and is the form nearly every project installs; terminals integral to the meter or service enclosure are furnished by some equipment makers and save the device where they exist, at the cost of a termination the communications installer needs the enclosure opened to reach; a separate bus bar near the service equipment is the form a building with many communications entrances uses, where a dozen bonding conductors land and the three terminals of a listed device would not do. {note}
−### The equipment grounding conductor is never required to be larger than the circuit conductors it accompanies.
+### The intersystem bonding termination shall provide not fewer than three terminals, shall be accessible without removing a cover or a finish, shall be connected to the service equipment enclosure, to the grounded service conductor or to the grounding electrode conductor by a conductor not smaller than 6 AWG copper, and shall not interfere with the opening of any enclosure.
−### Where ungrounded circuit conductors are increased in size for voltage drop or any other reason, the wire-type equipment grounding conductor shall be increased in size proportionally to the increase in circular mil area of the ungrounded conductors, in accordance with NEC 250.122(B).
+### The protector, surge arrester or cable shield of every telecommunications, television, antenna, radio and coaxial system entering the building shall be bonded to the intersystem bonding termination or to the grounding electrode system by a conductor the standard governing that system sizes, in accordance with NFPA 70 Chapter 8 and Article 810.
−### The Contractor shall verify that every upsized feeder carries a correspondingly upsized equipment grounding conductor.
+### The intersystem bonding termination exists so that the telephone, cable television, antenna and satellite installers who come after the building is finished have one labeled place to bond, instead of a clamp on the nearest water pipe. A protector grounded to a different electrode than the power system puts the difference in potential between the two electrodes across the equipment during a surge, which is how a lightning strike a mile away destroys a modem. {note}
−### Where a single equipment grounding conductor serves multiple circuits in the same raceway, it shall be sized for the largest overcurrent device protecting any conductor in that raceway, in accordance with NEC 250.122(C).
+# Separately Derived Systems {toc}
−### Equipment grounding conductors installed in parallel sets of conductors shall be sized in each raceway for the full overcurrent device rating, in accordance with NEC 250.122(F).
+## System Bonding Jumper {toc}
−### Proportional upsizing is routinely missed when a designer enlarges feeder conductors for voltage drop and leaves the ground at the table-minimum size. {note}
+### Each separately derived system, including the secondary of every transformer, the output of every generator whose neutral is switched in the transfer switch, and the output of every uninterruptible power supply whose output neutral is not solidly connected to the input neutral, shall be grounded and bonded in accordance with NFPA 70 250.30 and this article.
−# Bonding {toc}
+### A system bonding jumper shall be installed for each separately derived system, connecting the grounded conductor of the derived system to the equipment grounding conductor and the enclosure, at the location indicated in the datasheet and at no other point.
−## Bonding establishes electrical continuity between metallic parts so that an effective ground-fault current path exists and so that no objectionable difference of potential develops between accessible metal parts. {note}
−## Bonding is what makes the grounding system actually clear faults. {note}
−
−## Main Bonding Jumper {toc}
−
```datasheet
−label: Main Bonding Jumper
+label: System Bonding Jumper Location
type: radio
options:
− - "Factory-installed in service equipment"
− - "Field-installed per manufacturer instructions"
−default: "Factory-installed in service equipment"
+ - "At the source"
+ - "At the first disconnecting means"
+default: "At the source"
```
−### The main bonding jumper connects the equipment grounding conductor, the service-equipment enclosure, and the grounded (neutral) conductor together at the service, in accordance with NEC 250.24(B) and 250.28.
+### A system bonding jumper at the source, in the transformer or at the generator terminals, puts the bond where the derived neutral originates, makes the feeder from the source to the first disconnect a four-wire feeder with a separate equipment grounding conductor, and is where nearly every project puts it; a system bonding jumper at the first disconnecting means is chosen where the source is outdoors or inaccessible and the project wants the bond and the grounding electrode conductor in the switchboard, and it requires the supply-side bonding jumper between the source and the disconnect to be sized for the derived conductors under NFPA 70 250.30(A)(2). {note}
−### There shall be exactly one main bonding jumper for the service.
+### The system bonding jumper shall be sized in accordance with NFPA 70 250.28(D) from the largest ungrounded derived conductor, and shall be a bus, strap, screw or wire-type jumper as the Main Bonding Jumper article requires for a main bonding jumper.
−### The main bonding jumper shall be sized in accordance with NEC 250.28(D), generally not smaller than the values in Table 250.102(C)(1) based on the size of the service-entrance conductors.
+### The grounded conductor of a separately derived system shall be insulated from the enclosure at every point other than the system bonding jumper, and the Contractor shall remove any bonding strap or screw furnished at the point not selected.
−### Where service conductors exceed 1100 kcmil copper, the main bonding jumper shall be not less than 12.5 percent of the area of the largest ungrounded conductor.
+### Two system bonding jumpers on one derived system, one at the transformer and one at the panel it feeds, put the derived neutral current on the equipment grounding conductor between them, which is the downstream-bond defect of the Neutral Isolation Downstream of the Service article, moved one transformer down. NFPA 70 250.30(A)(1) says one point, and the datasheet is where that point is written down. {note}
−### The main bonding jumper is the single, intentional point at which the neutral and the ground are tied together for a service. {note}
+## Grounding Electrode Conductor of a Derived System {toc}
−## Neutral-to-Ground Connection Downstream {toc}
+### Each separately derived system shall be connected to the grounding electrode system by a grounding electrode conductor installed at the same point as the system bonding jumper, sized in accordance with NFPA 70 Table 250.66 from the largest ungrounded derived conductor, and arranged as indicated in the datasheet.
−### The grounded (neutral) conductor shall not be connected to equipment grounding conductors, enclosures, or the equipment grounding bus on the load side of the service disconnecting means, except as specifically permitted by NEC 250.142.
+```datasheet
+label: Derived System Grounding Electrode Conductor Arrangement
+type: radio
+options:
+ - "Individual conductor from each derived system to the nearest qualifying electrode"
+ - "Taps from a common grounding electrode conductor"
+ - "Connection to a ground bar bonded to the grounding electrode system"
+```
−### The Contractor shall verify that every downstream panelboard has its neutral bus isolated from the enclosure and that bonding screws or straps are removed at every panel except the service.
+### An individual conductor from each transformer to the nearest structural steel column or metal water pipe that is bonded to the electrode system is the arrangement NFPA 70 250.30(A)(5) describes first and the one a building with a few transformers uses; a common grounding electrode conductor of 3/0 copper or larger run through the building with a tap to each derived system under NFPA 70 250.30(A)(6) suits a high-rise or a plant with many transformers on one riser, where one conductor replaces a dozen; a ground bar in each electrical room, bonded to the electrode system and serving as the tap point for every derived system in the room, gives the same result with a landing the maintenance staff can see and test, and is the arrangement the electrical room standard provides for. {note}
−### Re-bonding the neutral to ground at a downstream panelboard creates parallel neutral paths that put normal load current onto raceways, equipment grounding conductors, and building steel. {note}
+### The electrode a derived system is connected to shall be the nearest of a metal in-ground support structure that is bonded to the electrode system or a metal water pipe electrode within 5 ft of its entrance, and where neither is available, another electrode of the grounding electrode system, in accordance with NFPA 70 250.30(A)(5).
−## Objectionable Current {toc}
+### Where the common conductor arrangement is selected, the common grounding electrode conductor shall be not smaller than 3/0 AWG copper or 250 kcmil aluminum, each tap shall be sized from the derived conductors of the system it serves, and the taps shall be connected to the common conductor by exothermic welding, by listed irreversible compression connectors or at a ground bar, so that the common conductor remains without splice.
−### The grounding and bonding system shall be arranged so that it does not carry objectionable current under normal operating conditions, in accordance with NEC 250.6.
+### Where the ground bar arrangement is selected, the bar shall be bonded to the grounding electrode system by a conductor sized in accordance with NFPA 70 Table 250.66 from the largest derived system or service it serves, and the conductor from each derived system to the bar shall be sized from that system's derived conductors.
−### Where objectionable current is detected during testing, the Contractor shall locate and correct the wiring error.
+### Where a structural steel column serves as the grounding electrode connection for a derived system, the structural metal shall itself be bonded to the grounding electrode system in accordance with the Bonding of Piping, Structure, and Other Metal Systems article, and the connection to the column shall be exothermic welded or a listed clamp applied to cleaned bare steel.
−### Objectionable current shall not be addressed by removing or interrupting grounding connections.
+## Generator, Transfer Switch, and UPS Sources {toc}
−### Objectionable current on grounding conductors is almost always a symptom of an improper neutral-to-ground connection downstream of the service, multiple service disconnects without proper treatment, or a wiring error. {note}
+### Whether a generator or uninterruptible power supply is a separately derived system follows from whether its neutral is switched in the transfer equipment or isolated from the normal source, a selection made under [[sync/automatic-transfer-switches]], [[sync/generator-paralleling-switchgear]] and [[sync/uninterruptible-power-supply-systems]], and the Contractor shall confirm that selection in writing before bonding the source.
−## Supply-Side and Load-Side Bonding Jumpers {toc}
+### Where the transfer equipment switches the neutral, the generator or UPS output shall be grounded and bonded as a separately derived system under this article, with its system bonding jumper at the source or at the first disconnecting means as the datasheet selects.
−### The supply-side bonding jumper bonds metallic enclosures and raceways on the line side of the service overcurrent device and shall be sized per NEC 250.102(C).
+### Where the transfer equipment does not switch the neutral, the generator or UPS output shall not be bonded to ground at the source, the neutral shall be carried unbroken to the service main bonding jumper, and the source frame, enclosure and sub-base tank shall be bonded to the equipment grounding conductor of the feeder only.
−### The load-side equipment bonding jumper bonds enclosures and raceways downstream of an overcurrent device and shall be sized per NEC 250.102(D), generally per Table 250.122.
+### Where a generator set is shipped with its neutral bonded to its frame and the transfer equipment does not switch the neutral, the Contractor shall remove the factory bond and record the removal on the continuity test report.
−### The Contractor shall confirm for each bonding jumper whether it is on the supply side or load side and size it accordingly.
+### A generator bonded at the set while the transfer switch carries a solid neutral has two neutral-to-ground bonds on the same system, one at the service and one at the generator, and the neutral current of every emergency load splits between the neutral and the ground path during a utility outage. A generator not bonded while the switch breaks the neutral has no ground reference at all when it is the only source. Either error passes every test performed on utility power and appears only in the first outage, which is why the neutral arrangement is confirmed in writing before the set is bonded. {note}
−### Supply-side jumpers must carry fault current with no upstream protection and are therefore sized more conservatively.
+# Equipment Grounding Conductors {toc}
−## Bonding at Service Equipment {toc}
+## Feeder and Branch Circuit Equipment Grounding {toc}
−### Metal raceways, cable armor, and enclosures containing service conductors shall be bonded together by a method that does not rely on locknuts and bushings alone, in accordance with NEC 250.92.
+### Every feeder shall carry the equipment grounding conductor indicated in the datasheet.
−### Acceptable methods include bonding jumpers around concentric or eccentric knockouts, bonding-type locknuts, bonding bushings, and threaded hubs.
+```datasheet
+label: Feeder Equipment Grounding Conductor
+type: radio
+options:
+ - "Wire-type conductor in every raceway and cable"
+ - "Metallic raceway or cable armor permitted as the conductor"
+default: "Wire-type conductor in every raceway and cable"
+```
−### Standard locknuts alone shall not be relied upon for service-conductor bonding because they cannot be assured to carry available service fault current.
+### Every branch circuit shall carry the equipment grounding conductor indicated in the datasheet.
−## Bonding of Piping and Building Metal {toc}
−
```datasheet
−label: Metallic Systems to be Bonded
−type: checkbox
+label: Branch Circuit Equipment Grounding Conductor
+type: radio
options:
− - "Metal water piping system"
− - "Metal gas piping (interior)"
− - "Structural building steel"
− - "Metal HVAC duct systems"
− - "Other interior metal piping likely to become energized"
−default: "Metal water piping system"
+ - "Wire-type conductor in every raceway and cable"
+ - "Metallic raceway or cable armor permitted as the conductor"
+default: "Wire-type conductor in every raceway and cable"
```
−### Metal water piping systems, metal gas piping, and structural metal that is interconnected to form a building frame shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor, or the grounding electrodes, in accordance with NEC 250.104.
+### NFPA 70 250.118 recognizes rigid metal conduit, intermediate metal conduit, electrical metallic tubing, listed cable armor and several other wiring methods as equipment grounding conductors in their own right, and a project that relies on them saves a conductor in every raceway. A wire-type conductor in every raceway gives a fault path that does not depend on every coupling, connector and locknut staying tight for the life of the building, survives a corroded or separated raceway, and is what nearly every commercial, institutional and industrial project specifies for feeders and branch circuits alike; relying on the raceway is the arrangement of a project under cost pressure with a well-supervised raceway installation, and it is more often accepted for branch circuits in threaded conduit than for feeders, which is why the two circuit classes are selected separately. {note}
−### The bonding jumper for the metal water piping system shall be sized per NEC Table 250.102(C)(1) based on the service conductors.
+### Where a metallic raceway or cable armor is relied on as the equipment grounding conductor, every joint shall be made up wrench-tight, every connector and coupling shall be listed for grounding, no raceway run shall include a nonmetallic section, expansion fitting or flexible section without a bonding jumper across it, and the raceway shall be bonded at each enclosure by a means the Bonding of Service Raceways and Enclosures article recognizes wherever a concentric or eccentric knockout or a reducing washer interrupts the metal-to-metal contact.
−### Bonding of metal building frame and interior piping shall be sized per NEC 250.104 based on the circuit likely to energize the piping.
+### A wire-type equipment grounding conductor shall be installed in every raceway and cable within a hazardous (classified) location and in the raceway path from that location back to the service or the derived system, and in every raceway and cable serving a patient care space, an isolated-ground circuit, a swimming pool or fountain, or an agricultural building, whatever the datasheet selects.
−## Intersystem Bonding Termination {toc}
+### The equipment grounding conductor of every circuit shall be run in the same raceway, cable or trench as the circuit conductors it serves, in accordance with NFPA 70 300.3(B) and 250.134.
+## Flexible Conduit and Cord {toc}
+
+### The equipment grounding of every length of flexible metal conduit, liquidtight flexible metal conduit and liquidtight flexible nonmetallic conduit shall be as indicated in the datasheet.
+
```datasheet
−label: Intersystem Bonding Termination
+label: Flexible Conduit Equipment Grounding
type: radio
options:
− - "Listed external termination block (minimum 3 terminals)"
− - "Listed termination integral to service equipment"
−default: "Listed external termination block (minimum 3 terminals)"
+ - "Wire-type conductor in every length of flexible conduit"
+ - "Flexible metal conduit relied on as the conductor within the limits of NFPA 70 250.118"
+default: "Wire-type conductor in every length of flexible conduit"
```
−### An intersystem bonding termination shall be provided at the service equipment and at any disconnecting means for buildings supplied by a feeder, in accordance with NEC 250.94.
+### NFPA 70 250.118 permits flexible metal conduit and liquidtight flexible metal conduit to serve as the equipment grounding conductor only in short lengths, on small circuits, with listed fittings and where flexibility is not needed after installation. A wire-type conductor in every length of flex removes the question for the inspector and the maintenance electrician and is what nearly every project specifies, because a flex whip to a motor or a transformer is exactly the place where vibration loosens a fitting; relying on the flex within the code limits is the arrangement of a lighting whip or a short connection to a fixed appliance on a project that accepts the limits and polices them. {note}
−### The intersystem bonding termination shall provide an accessible point with at least three terminals for bonding communications, CATV, antenna, and other systems to the building grounding electrode system.
+### Liquidtight flexible nonmetallic conduit and every flexible connection to equipment that vibrates or is moved for service shall contain a wire-type equipment grounding conductor sized for the circuit, whatever the datasheet selects.
−### The Contractor shall install the intersystem bonding termination so that it remains accessible after all other equipment is in place; it shall not be located behind equipment or finishes.
+### Cord-and-plug-connected equipment shall be grounded through the equipment grounding conductor of the cord and the grounding contact of the plug, and the box or enclosure the receptacle is mounted in shall be bonded to the circuit's equipment grounding conductor in accordance with NFPA 70 250.146 and 250.148.
−# Separately Derived Systems {toc}
+## Wire-Type Conductor Material and Covering {toc}
−## A separately derived system has no direct electrical connection of circuit conductors to conductors of another system. {note}
+### Wire-type equipment grounding conductors shall be of the material indicated in the datasheet.
−## Each separately derived system shall be grounded and bonded at the source in accordance with NEC 250.30.
+```datasheet
+label: Wire-Type Equipment Grounding Conductor Material
+type: radio
+options:
+ - "Copper"
+ - "Aluminum"
+ - "Copper-clad aluminum"
+default: "Copper"
+```
−## The secondary of an isolation or dry-type distribution transformer, the output of an on-site generator with a transfer switch that switches the neutral, and the output of certain uninterruptible power supplies are separately derived systems; each is, in effect, a new source. {note}
+### A copper equipment grounding conductor terminates on any listed lug, runs with copper or aluminum circuit conductors, and is what nearly every project installs; an aluminum or copper-clad aluminum conductor costs less on a large feeder and is chosen where the feeder conductors are aluminum and the terminations are already rated for it, and NFPA 70 250.120(B) bars it from direct contact with masonry, from earth, from corrosive conditions and from termination within 18 in. of earth. {note}
−## System Bonding Jumper {toc}
+### Wire-type equipment grounding conductors shall be covered as indicated in the datasheet, and an insulated or covered conductor shall be continuous green or green with one or more yellow stripes along its entire length, in accordance with NFPA 70 250.119, except that a conductor larger than 6 AWG may be identified green at each end and at every point where it is accessible.
```datasheet
−label: System Bonding Jumper Location
+label: Wire-Type Equipment Grounding Conductor Covering
type: radio
options:
− - "At the source (transformer or generator)"
− - "At the first system disconnecting means"
−default: "At the source (transformer or generator)"
+ - "Insulated, green"
+ - "Bare"
+default: "Insulated, green"
```
−### A system bonding jumper shall be installed for each separately derived system, connecting the equipment grounding conductor of the derived system to the grounded (neutral) conductor, in accordance with NEC 250.30(A)(1).
+### An insulated green conductor is identifiable in a crowded box or gutter and cannot touch a live terminal in a panel, and it is what nearly every project specifies in raceway; a bare conductor is permitted by NFPA 70, saves the insulation cost on a large feeder, is the conductor inside a listed cable assembly, and is chosen for a feeder in a dedicated raceway or a tray where nothing else can contact it. {note}
−### The system bonding jumper shall be installed at a single point, either at the source itself or at the first system disconnecting means, but not at both.
+### Green or green-with-yellow-stripe insulation shall not be used for any conductor other than an equipment grounding conductor or a grounding electrode conductor.
−### The system bonding jumper shall be sized per NEC 250.30(A)(1) and Table 250.102(C)(1), based on the derived phase conductors.
+## Equipment Grounding Conductor Size {toc}
−### Installing a system bonding jumper at two points re-creates the same parallel-neutral problem as a downstream neutral-to-ground bond. {note}
+### Every wire-type equipment grounding conductor shall be sized in accordance with NFPA 70 Table 250.122 from the rating of the overcurrent device ahead of the circuit, and shall not be required to be larger than the circuit conductors it accompanies.
−## Grounding Electrode Conductor for Separately Derived Systems {toc}
+### Where the ungrounded conductors of a circuit are increased in size above the minimum their ampacity requires, for voltage drop or any other reason, the wire-type equipment grounding conductor shall be increased in size in proportion to the increase in circular mil area of the ungrounded conductors, in accordance with NFPA 70 250.122(B), and the Contractor shall verify the increase on every feeder shown upsized on [[drawing: the one-line diagram and feeder schedule]].
−```datasheet
−label: Separately Derived System Grounding Electrode
−type: select
−options:
− - "Nearest effectively grounded structural metal"
− - "Nearest effectively grounded metal water pipe (within 5 ft of entry)"
− - "Building grounding electrode system / common GEC"
−default: "Building grounding electrode system / common GEC"
−```
+### Where one equipment grounding conductor serves several circuits in one raceway, cable or tray, it shall be sized from the largest overcurrent device protecting any of those circuits, in accordance with NFPA 70 250.122(C).
−### Each separately derived system shall be connected to a grounding electrode by a grounding electrode conductor, in accordance with NEC 250.30(A)(4) and (A)(5).
+### Where circuit conductors are installed in parallel in more than one raceway or cable, a wire-type equipment grounding conductor shall be installed in each raceway or cable and each shall be sized for the full rating of the overcurrent device, in accordance with NFPA 70 250.122(F).
−### The grounding electrode shall be the nearest of an effectively grounded structural metal member or the nearest effectively grounded metal water pipe; where neither is available, another electrode of the building grounding electrode system shall be used.
+### The equipment grounding conductor to a motor shall be sized from the rating of the branch-circuit short-circuit and ground-fault protective device, in accordance with NFPA 70 250.122(D).
−### The grounding electrode conductor shall be sized per NEC Table 250.66 based on the derived phase conductors and connected at the same single point as the system bonding jumper.
+### A feeder upsized two sizes for voltage drop with its equipment grounding conductor left at the table value is the defect a reviewer finds most often in a feeder schedule, and it leaves the fault path with a higher impedance than the circuit it protects. The proportional rule exists so that the fault current on a long feeder still rises high enough, fast enough, to open the breaker. {note}
−### Where there are multiple separately derived systems, a common grounding electrode conductor with taps to each system is permitted by NEC 250.30(A)(6).
+## Bonding of Enclosures, Boxes, and Equipment Frames {toc}
−### The common grounding electrode conductor shall be sized for the largest derived system it serves.
+### Every enclosure, cabinet, box, frame, rack, pedestal, pole, tray, wireway, busway housing, motor frame, transformer case, generator frame and other normally non-current-carrying metal part of electrical equipment shall be bonded to the equipment grounding conductor of the circuit that serves it, by a listed terminal, lug, bonding jumper or grounding screw, in accordance with NFPA 70 250.110 through 250.136.
−### A common grounding electrode conductor is often the cleanest installation in a building with many dry-type transformers. {note}
+### Where an equipment grounding conductor enters a metal box, it shall be bonded to the box by a listed grounding screw used for no other purpose, a listed grounding clip or a listed device, and every equipment grounding conductor in the box shall be spliced or joined so that the removal of a device does not interrupt the grounding continuity of the other conductors, in accordance with NFPA 70 250.148.
−## Generators and Transfer Switches {toc}
+### Every metal wireway, auxiliary gutter and cable tray shall be made electrically continuous across each joint, shall be bonded to the equipment grounding conductor of the largest circuit it contains, and where it contains more than one circuit shall carry or be bonded to an equipment grounding conductor sized in accordance with the Equipment Grounding Conductor Size article for that circuit.
+### The ground bus of every switchgear, switchboard, motor control center, drive lineup and other assembly rated above or below 1000 V shall be bonded to the grounding electrode system by a conductor sized in accordance with NFPA 70 Table 250.66 from the service or derived conductors supplying the assembly, or in accordance with Table 250.122 from the feeder overcurrent device where the assembly is fed by a feeder.
+
+### The grounding terminal of every industrial control panel, instrument enclosure, network cabinet and equipment rack shall be bonded to the equipment grounding conductor of the circuit serving it, and an isolated instrument or signal reference ground bus furnished inside such an enclosure under [[sync/industrial-control-panels]] shall be connected to the grounding electrode system by one insulated conductor not smaller than 6 AWG copper at one point only.
+
+### Every metal pole shall be bonded to the equipment grounding conductor of its circuit at a grounding terminal inside the handhole, and the grounding terminal of every meter, transmitter, valve actuator and similar field instrument shall be bonded to the equipment grounding conductor of the raceway or cable serving it.
+
+### Where a raised access floor understructure, an equipment room grid or a signal reference grid is used as part of the grounding system, the understructure or grid shall be bonded to the room ground bar and to the equipment grounding conductors of the circuits in the room, and shall supplement and never replace the equipment grounding conductor of any circuit.
+
+# Isolated-Ground Circuits {toc}
+
+## Isolated-ground branch circuits shall be provided as indicated in the datasheet, and where provided shall serve the outlets indicated on [[drawing: the electrical plans]].
+
```datasheet
−label: Generator Neutral Treatment
+label: Isolated-Ground Branch Circuits
type: radio
options:
− - "Switched neutral — generator is a separately derived system"
− - "Solid (non-switched) neutral — generator is not separately derived"
−default: "Solid (non-switched) neutral — generator is not separately derived"
+ - "Not used"
+ - "Provided"
+default: "Not used"
```
−### Where the transfer switch switches the neutral, the generator is a separately derived system and shall have its own system bonding jumper and grounding electrode connection.
+## An isolated-ground circuit carries an insulated equipment grounding conductor that passes through the boxes and panelboards on its route without bonding to them, so that the grounding terminal of the receptacle sees only the grounding point of its source and not the noise current circulating on the raceway system. It is specified for recording, laboratory and some medical instrumentation whose maker requires it, and it is specified far more often than that for ordinary office and data equipment whose power supplies do not need it, where it adds a conductor, an insulated bus and a receptacle to every outlet and buys nothing measurable. {note}
−### Where the transfer switch does not switch the neutral, the generator is not a separately derived system and shall not have a neutral-to-ground bond at the generator, because the service main bonding jumper already provides it.
+## The insulated equipment grounding conductor of each isolated-ground circuit shall be routed with the circuit conductors and shall follow the path indicated in the datasheet to the grounding point of the service or the separately derived system that supplies the circuit, in accordance with NFPA 70 250.146(D).
−### The Contractor shall confirm the transfer switch neutral arrangement before bonding the generator and shall coordinate this with [[sync/emergency-and-standby-power]].
+```datasheet
+label: Isolated Grounding Conductor Path
+type: radio
+options:
+ - "Collected on an isolated ground bus in the serving panelboard, with one insulated conductor from that bus to the grounding point of the source"
+ - "Run unbroken from each outlet to the grounding point of the source"
+default: "Collected on an isolated ground bus in the serving panelboard, with one insulated conductor from that bus to the grounding point of the source"
+```
−# Ground Bus and Ground Bars {toc}
+## Collecting the isolated conductors on an insulated bus in the panelboard, furnished under [[sync/panelboards]], and running one insulated conductor from that bus to the transformer or service grounding point is the arrangement nearly every isolated-ground design uses, because it keeps the home runs short and gives the maintenance electrician one conductor to test; running each conductor unbroken to the source is the arrangement an instrument maker's grounding specification sometimes requires, and it multiplies the conductors in the feeder raceway by the number of outlets. {note}
−## Equipment Ground Bus in Distribution Equipment {toc}
+## The isolated equipment grounding conductor shall be insulated along its entire length, shall not be bonded to any box, raceway, enclosure or panelboard cabinet it passes through, and shall terminate only at the isolated ground bus or at the grounding point of the source.
−### Every panelboard, switchboard, and distribution assembly shall be provided with an equipment grounding bus or terminal bar to which all equipment grounding conductors entering the enclosure are terminated, in accordance with NEC 408.40.
+## The raceway, the boxes and the ordinary equipment grounding conductor of an isolated-ground circuit shall be installed and bonded as for any other circuit, and the isolated conductor shall be in addition to, and never in place of, that grounding path.
−### Each equipment grounding conductor shall terminate in an individual terminal; more than one conductor per terminal is permitted only where the terminal is listed for multiple conductors.
+## The isolated equipment grounding conductor shall not be connected to a separate electrode, to the structure or to any point other than the grounding point of the source, and an isolated-ground circuit that is grounded only to an electrode is a code violation that leaves the receptacle with no fault-clearing path.
−### The equipment ground bus shall be bonded to the enclosure.
+## Every isolated-ground receptacle, furnished under [[sync/wiring-devices]], shall be identified by an orange triangle on its face, and every isolated-ground circuit shall be identified as such in the panelboard directory.
−## Telecommunications and Sensitive-Equipment Ground Bars {toc}
+# Bonding of Piping, Structure, and Other Metal Systems {toc}
+## Code-Required Bonding of Piping and Structural Metal {toc}
+
+### The metal water piping system of each building shall be bonded to the service equipment enclosure, to the grounded service conductor, to the grounding electrode conductor or to a grounding electrode, in accordance with NFPA 70 250.104(A), by a bonding jumper sized in accordance with NFPA 70 Table 250.102(C)(1) from the service-entrance conductors and of the size indicated in the datasheet.
+
```datasheet
−label: Dedicated Ground Bar Material and Finish
−type: radio
+label: Water Piping Bonding Jumper Size
+type: select
+unit: AWG/kcmil
+derived: "the service-entrance conductors, per NFPA 70 Table 250.102(C)(1)"
options:
− - "Copper, electro-tin plated"
− - "Copper, bare"
−default: "Copper, electro-tin plated"
+ - "8 AWG"
+ - "6 AWG"
+ - "4 AWG"
+ - "2 AWG"
+ - "1/0 AWG"
+ - "2/0 AWG"
+ - "3/0 AWG"
+ - "250 kcmil"
+ - "350 kcmil"
+ - "500 kcmil"
+default: derived
```
+### The metal water piping in the area served by each separately derived system shall be bonded to the grounded conductor at the system bonding jumper, to the grounding electrode conductor of that system or to its electrode, by a jumper sized in accordance with NFPA 70 Table 250.102(C)(1) from the derived conductors, in accordance with NFPA 70 250.104(D).
+
+### Every metal gas piping system, including corrugated stainless steel tubing, shall be bonded to the service equipment enclosure, the grounded service conductor, the grounding electrode conductor or a grounding electrode by a jumper sized in accordance with NFPA 70 Table 250.122 from the largest circuit likely to energize the piping and not smaller than 6 AWG copper, in accordance with NFPA 70 250.104(B), and the bonding of the gas piping shall be coordinated with the connection point and the fittings [[sync/natural-gas-piping]] and [[sync/fuel-gas-piping]] provide for it.
+
+### Exposed structural metal that is interconnected to form a building frame and is not intentionally grounded or bonded shall be bonded to the service equipment enclosure, the grounded service conductor, the grounding electrode conductor or a grounding electrode by a jumper sized in accordance with NFPA 70 Table 250.102(C)(1) from the service-entrance conductors, in accordance with NFPA 70 250.104(C), and the connection shall be made to a column at a point cleaned to bare steel.
+
+### Other metal piping that is likely to become energized, including sprinkler, process, compressed air, fuel oil and hydronic piping with an electric pump, heater or valve on it, shall be bonded in accordance with NFPA 70 250.104(B) by the equipment grounding conductor of the circuit likely to energize it, and the equipment grounding conductor of that circuit shall be the bonding means.
+
+### Every bonding jumper to piping or structure shall be connected by a listed pipe clamp, a listed clamp for structural steel, an exothermic weld or a listed lug on a tapped hole, applied to a surface cleaned to bare metal, and shall be accessible except where it is exothermic welded or is a listed connector embedded in concrete.
+
+### The water pipe, the gas pipe and the building steel are bonded so that a fault that energizes them, from a water heater element, a furnace igniter or a conduit chafed against a beam, trips the breaker instead of leaving the pipe at line voltage for the next person to touch it. The bond is sized from the service, not from the circuit, because the pipe can be energized by any circuit in the building. {note}
+
+## Supplementary Bonding of Metal Systems {toc}
+
+### The metal systems indicated in the datasheet shall be bonded to the grounding electrode system or to the equipment grounding conductor of the nearest electrical equipment, in addition to the systems NFPA 70 250.104 requires, by a conductor not smaller than 6 AWG copper connected by a listed clamp, lug or exothermic weld at a point cleaned to bare metal.
+
```datasheet
−label: Ground Bar Provided In
+label: Supplementary Bonding of Metal Systems
type: checkbox
options:
− - "Main electrical room"
− - "Each electrical room / closet"
− - "Telecommunications rooms"
− - "Generator / standby power room"
− - "Data center / equipment rooms"
−default: "Main electrical room"
+ - "Metal duct systems"
+ - "Fire sprinkler and standpipe piping"
+ - "Process and compressed air piping"
+ - "Metal roof and wall panels"
+ - "Metal doors, frames, ladders and racks in electrical rooms"
+ - "Water storage tanks"
+ - "Fuel storage tanks and fuel piping"
+ - "Static-dissipative flooring ground connections"
+constraint: all_of
```
−### Where the project includes telecommunications rooms, equipment rooms, or sensitive-equipment areas, a dedicated ground bar shall be provided and bonded to the building grounding electrode system.
+### None of these systems is required by NFPA 70 to be bonded unless it is likely to become energized, and a project adds them for reasons of its own: metal duct and sprinkler piping to give a lightning-exposed or electronics-heavy building an equipotential structure, metal roof and wall panels where a lightning protection system under [[sync/lightning-protection]] or a corporate standard asks for it, the doors, frames, ladders and racks of an electrical room under [[sync/electrical-rooms]] so that nothing a worker touches during a fault is at a different potential from the equipment, water and fuel tanks under [[sync/water-storage-tanks]], [[sync/fuel-dispensing-and-storage-tanks]] and [[sync/fuel-oil-systems]] for lightning and static, and the connections of a static-dissipative floor under [[sync/resinous-flooring]] because the floor's maker requires a ground reference. Each adds conductors and clamps and buys an equipotential surface where the project values one. {note}
−### Telecommunications bonding shall be coordinated with ANSI/TIA-607 and with [[sync/telecommunications-bonding]].
+### Where fuel storage tanks and fuel piping are selected, the tank, its fill and vent connections and its piping shall be bonded to the grounding electrode system, and a listed bonding terminal for the delivery vehicle's static bond shall be provided within 3 ft of the fill connection.
−### The electrical Contractor's responsibility under this standard is the bonding conductor from the building grounding electrode system to the primary telecommunications ground bar; the telecommunications bonding backbone itself is a separate scope. {note}
+### Where a cathodically protected tank or piping is bonded under this article, the bond shall be made through the decoupling device [[sync/cathodic-protection]] furnishes and shall not be omitted.
−# Connections and Terminations {toc}
+## Bonding Across Fittings and Meters {toc}
−## The integrity of the grounding system depends entirely on the quality of its connections. {note}
−## A grounding conductor that is correctly sized but poorly terminated provides no protection. {note}
+### A bonding jumper shall be installed around every water meter, filter, strainer, dielectric fitting, flexible connector, expansion joint and other removable or insulating device in a bonded piping system, sized as the bonding jumper for that system is sized, long enough to permit removal of the device without disconnecting the jumper.
−## Connection Methods {toc}
+### A bonding jumper shall be installed across every expansion fitting, telescoping section, flexible section and nonmetallic section of a metal raceway system, and across every joint in a raceway run that is not made up by a threaded or listed grounding coupling.
−```datasheet
−label: Connection Method — Buried or Concrete-Encased
−type: radio
−options:
− - "Exothermic welded"
− - "Listed irreversible compression connector"
−default: "Exothermic welded"
−```
+### Where an underground duct bank enters a manhole, vault or building, the metallic conduits, the cable racks and the pulling irons of each personnel-accessible structure shall be bonded to a rod electrode or a ground bar in the structure that is bonded to the grounding electrode system, and the structure's grounding provisions furnished under [[sync/underground-ductbank]] and [[sync/site-concrete-structures]] shall be connected under this standard.
−```datasheet
−label: Connection Method — Accessible Locations
−type: select
−options:
− - "Exothermic welded"
− - "Listed irreversible compression connector"
− - "Listed mechanical connector / lug"
−default: "Listed mechanical connector / lug"
−```
+## Bonding in Hazardous (Classified) Locations {toc}
−### Connections that are buried in earth, encased in concrete, or otherwise inaccessible after construction shall be made by exothermic welding or by listed irreversible compression connectors.
+### Every metal raceway, fitting, box and enclosure within a hazardous (classified) location, and every one in the raceway path from that location back to the service equipment or to the grounding point of the separately derived system that supplies it, shall be bonded by a bonding jumper with listed fittings, by a bonding-type locknut or bushing, or by a threaded connection made up wrench-tight, in accordance with NFPA 70 250.100, and never by a standard locknut and bushing alone, regardless of the voltage of the circuit.
−### Mechanical connections shall not be used in inaccessible locations.
+### The bonding means within the classified location and the seals, drains and wiring methods there are governed by [[sync/electrical-hazardous-locations]], and this standard governs the bonding of the raceway path outside the location back to the source.
−### In accessible locations, listed mechanical connectors and lugs are permitted.
+### A loose locknut outside a classified location is as much a source of ignition for the fault current passing through it toward the location as one inside, because the current from a fault in the wet well flows through every fitting between the wet well and the switchboard. That is why the bonding requirement runs all the way back to the source. {note}
−### Mechanical connectors shall be listed for the conductor material and size and shall be tightened to the manufacturer's specified torque using a calibrated torque tool.
+# Interfaces with Other Grounded Systems {toc}
−### Exothermic welding and listed irreversible compression connectors create a permanent connection that cannot loosen, corrode at a mechanical interface, or be disturbed. {note}
+## Lightning Protection System {toc}
−## General Connection Requirements {toc}
+### Where a lightning protection system is installed under [[sync/lightning-protection]], its grounding electrodes shall be bonded to the grounding electrode system of the building by a main-size conductor of that system connected at the point indicated on [[drawing: the grounding riser diagram]], in accordance with NFPA 70 250.106 and NFPA 780, and the common bonding connection shall be made under this standard.
−### Connection of a grounding electrode conductor or bonding jumper to an electrode or to equipment shall be made by listed lugs, listed pressure connectors, exothermic welding, or other listed means, in accordance with NEC 250.70.
+### The connection between the two systems shall be exothermic welded or a listed irreversible compression connection, and shall be made to the grounding electrode conductor, to a ground bar bonded to the electrode system or to the ground ring, and never to a panelboard ground bus alone.
−### Connections shall not depend on solder, because solder melts at fault-current temperatures.
+### The lightning protection electrodes shall not be used as the grounding electrode system of the electrical service, and the electrical service electrodes shall not be used as the lightning protection electrodes.
−### No more than one conductor shall be terminated under a single connector unless the connector is listed for multiple conductors.
+### A building with a lightning ground and an electrical ground that are not bonded has two earth references that can differ by tens of thousands of volts during a strike, and that difference appears across every circuit that touches both. Bonding them makes the whole building rise and fall together, which is the only condition under which nothing inside it is damaged. {note}
−### Surfaces to be connected shall be cleaned of paint, enamel, mill scale, and coatings to bare metal at the point of connection, and the connection shall be made directly on the cleaned conductive surface.
+## Telecommunications Bonding {toc}
−### Where a coating must be restored after connection, a corrosion-inhibiting compound listed for the purpose shall be applied.
+### The telecommunications bonding conductor from the primary bonding busbar shall be connected to the grounding electrode system at the service equipment ground bus, at the grounding electrode conductor or at a ground bar bonded to the electrode system, at the point indicated on [[drawing: the grounding riser diagram]], and that connection shall be made under this standard.
−## Earth-Contact Connectors {toc}
+### The connection of the telecommunications bonding conductor at the electrode system shall be exothermic welded or a listed irreversible compression connection, shall be made to a terminal that is not shared with any other conductor, and shall be the only point at which the telecommunications bonding infrastructure is connected to the electrode system.
−### Connectors used in direct contact with the earth or in concrete shall be listed for direct burial or concrete encasement, in accordance with NEC 250.70.
+### The size and routing of the telecommunications bonding conductor and everything downstream of the primary bonding busbar are governed by [[sync/telecommunications-bonding]] and ANSI/TIA-607, and the support and protection of that conductor where it runs through electrical spaces shall be as this standard requires for a grounding electrode conductor.
−### Connectors not so listed shall not be buried or encased.
+## Cathodic Protection Interface {toc}
−# Conductors {toc}
+### Where a cathodic protection system under [[sync/cathodic-protection]] protects a structure that NFPA 70 Article 250 requires to be bonded, the bond shall be installed under this standard, the decoupling device in the bond shall be furnished and tested under that standard, and no electrical safety bond shall be omitted, removed or interrupted on account of the cathodic protection system.
−## Grounding and bonding conductors shall be copper conforming to ASTM B3 and ASTM B8, except where aluminum is specifically permitted by NEC 250.64(A) and selected on the contract documents.
+### The rectifier enclosure and the anode junction box of a cathodic protection system shall be bonded to the equipment grounding conductor of the rectifier branch circuit as electrical equipment under this standard, and the rectifier negative output shall not be connected to the equipment grounding conductor.
−## Bare grounding conductors used as electrodes or buried shall be soft-drawn copper.
+## Direct-Current Control Systems {toc}
−# Ground Bars and Busbars {toc}
+### Each direct-current control system supplied by a station battery under [[sync/dc-battery-systems]] shall be grounded or left ungrounded as indicated in the datasheet, in accordance with NFPA 70 250.162 and 250.164.
−## Ground bars and busbars shall be copper conforming to ASTM B187.
+```datasheet
+label: Direct-Current Control System Grounding
+type: radio
+options:
+ - "Ungrounded, with ground-fault detection"
+ - "One pole solidly grounded"
+ - "Battery midpoint grounded"
+default: "Ungrounded, with ground-fault detection"
+```
−## Tin plating shall be provided where specified to reduce contact-surface oxidation and to ease future re-termination.
+### An ungrounded DC control system keeps operating through its first ground fault, which is the property a protective-relay battery is installed for, and NFPA 70 250.162(A) permits it for an industrial system equipped with a ground detector; it is the arrangement of nearly every switchgear, generating station and plant control battery. A solidly grounded pole trips the circuit on the first ground fault and is chosen where the DC system serves equipment whose maker requires a grounded supply, such as some telecommunications rectifier plants; a grounded battery midpoint halves the voltage to ground of each pole and is the arrangement of a few high-voltage battery systems and some traction-style supplies. {note}
−# Ground Rods {toc}
+### Where the DC system is grounded, the grounding electrode conductor shall be sized in accordance with NFPA 70 250.166 and connected to the grounding electrode system at the source, and the DC bonding jumper shall be sized in accordance with NFPA 70 250.168.
−## Ground rod electrodes shall conform to NEMA GR 1 and shall be listed to UL 467.
+### Where the DC system is ungrounded, a ground detector shall be furnished under [[sync/dc-battery-systems]], and the battery rack, the battery cabinet, the charger enclosure, the DC panel enclosure and the raceway of the DC circuits shall be bonded to the equipment grounding conductor of the AC circuit supplying the charger and to the building grounding electrode system.
−## Copper-bonded steel rods shall have a copper bonding thickness sufficient to survive driving without exposing the steel core and to provide corrosion life appropriate to the soil conditions.
+# Special Occupancy Provisions {toc}
−# Connectors and Clamps {toc}
+## Where the project includes any of the occupancies indicated in the datasheet, the grounding and bonding of that occupancy shall meet the additional provisions of this article and of the NFPA 70 article that governs it, and those provisions shall govern over the general requirements of this standard where they differ.
−## All connectors, clamps, bushings, and bonding devices shall be listed and labeled to UL 467 and shall be of materials compatible with the conductors and surfaces they contact to avoid galvanic corrosion.
+```datasheet
+label: Special Occupancy Grounding Provisions
+type: checkbox
+options:
+ - "Patient care spaces"
+ - "Swimming pools, spas, fountains and water features"
+ - "Agricultural buildings"
+ - "Information technology equipment rooms"
+constraint: all_of
+```
−## Connectors of dissimilar metal to the conductor or the contacted surface shall not be used in damp, wet, or buried locations.
+## In every patient care space, each branch circuit shall be installed in a metal raceway or cable armor that qualifies as an equipment grounding conductor and shall also contain an insulated copper equipment grounding conductor, so that the grounding path is redundant, in accordance with NFPA 70 517.13, and the receptacles and fixed equipment in the space shall be bonded through both paths; the essential electrical system that supplies those circuits is governed by [[sync/healthcare-essential-electrical-systems]].
−# Isolated and Insulated Grounding {toc}
+## At every permanently installed swimming pool, spa, hot tub and fountain, the reinforcing steel or a copper grid in the shell and deck, the metal forming shells, ladders, rails, fittings and fences within the distances NFPA 70 680.26 states, the pump motors and the metal piping shall be bonded together by solid copper conductor not smaller than 8 AWG into one equipotential bonding grid, and the grid shall be connected to the equipment grounding conductor of the pool equipment and not to a separate electrode.
−## An isolated (insulated) equipment grounding conductor is an additional, insulated equipment grounding conductor that bypasses the normal raceway-and-enclosure grounding path and connects a receptacle's grounding terminal directly back to an upstream point, in accordance with NEC 250.146(D). {note}
+## In every agricultural building with livestock, an equipotential plane shall be installed in the concrete floor of each area where livestock stand and electrical equipment is present, bonded to the equipment grounding conductor of the building's electrical system by solid copper conductor not smaller than 8 AWG, in accordance with NFPA 70 547.10.
−## The intent of an isolated equipment grounding conductor is to reduce coupling of electrical noise into sensitive electronic equipment by avoiding the shared, multi-point grounding of the conduit system. {note}
+## In every information technology equipment room, the signal reference grid, the raised floor understructure under [[sync/raised-access-flooring]], the equipment racks and the power distribution units shall be bonded to the room ground bar and to the equipment grounding conductors of the circuits in the room in accordance with NFPA 70 645.15 and IEEE 1100, and no isolated or separate electrode shall be installed for the room's equipment.
−## Where isolated ground receptacles are used, the isolated equipment grounding conductor is permitted to pass through panelboards and enclosures without bonding to them, but it shall ultimately terminate at the applicable derived-system or service grounding point.
+## Each of these occupancies puts a person, an animal or a sensitive load in contact with grounded metal under conditions where a few volts of difference matters: a patient with a catheter in a vessel, a swimmer in water, a cow on wet concrete, a server whose signal reference drifts. The code answer in every case is the same, more bonding and never a separate ground, because a separate electrode is exactly what creates the difference in potential. {note}
−## The isolated ground shall not be terminated at earth alone, and the connection back to the source shall not be omitted; an isolated ground is still a grounding conductor and shall provide an effective fault-clearing path.
+# Ground Bars {toc}
−## The metal raceway and any normal equipment grounding conductor shall still be installed and bonded; the isolated ground is in addition to, never in place of, the standard grounding path.
+## Ground bars shall be provided where indicated on [[drawing: the grounding riser diagram]] and wherever another standard requires one, and each shall be a copper bar conforming to ASTM B187, not less than 1/4 in. thick and 2 in. high, of the length the number of conductors landed on it requires with not fewer than four spare terminal positions, predrilled for two-hole compression lugs on NEMA spacing, and mounted on listed insulating standoffs.
−## The Engineer should confirm that the connected equipment actually requires an isolated ground before specifying it.
+## Ground bars shall be finished as indicated in the datasheet.
```datasheet
−label: Isolated Ground Receptacles
+label: Ground Bar Plating
type: radio
options:
− - "Not used"
− - "Provided at designated sensitive-equipment locations"
−default: "Not used"
+ - "Electro-tin plated"
+ - "Bare copper"
+default: "Electro-tin plated"
```
−## Where isolated ground receptacles are installed, they shall be identified by the orange triangle marking required by NEC 406.3(E).
+## A tin-plated bar presents a surface that does not oxidize under a lug, accepts aluminum and copper lugs without an antioxidant compound, and is what nearly every ground bar on a building project is; a bare copper bar is cheaper, is the bar a telecommunications standard sometimes names for its busbars, and needs its contact surfaces cleaned and treated at every termination. {note}
−## Isolated grounding is frequently specified where it provides no benefit, and modern electronic equipment with properly designed power supplies generally does not require it. {note}
+## Every ground bar that serves as the grounding point or tap point of one or more separately derived systems shall be bonded to the grounding electrode system by a conductor sized in accordance with NFPA 70 Table 250.66 from the largest service or derived system it serves, and every ground bar that serves only to collect equipment grounding conductors shall be bonded by a conductor sized in accordance with NFPA 70 Table 250.122 from the largest overcurrent device supplying the equipment landed on it.
−# Special Occupancy Considerations {toc}
+## Each conductor landed on a ground bar shall terminate in its own two-hole compression lug or its own listed terminal, no terminal shall carry more than one conductor unless it is listed for that number, and the bar shall be labeled as the Identification article requires.
−## Certain occupancies impose grounding and bonding requirements beyond the general rules of NEC Article 250. {note}
+## A ground bar in an electrical room, furnished where [[sync/electrical-rooms]] requires one, is the place the room's equipment grounds, the derived system taps and the bonding conductors of the room's doors, racks and trays are brought together and can be seen and tested; a bar that is connected to the electrode system by a conductor too small for the derived systems it serves defeats that purpose, which is why the bar's bonding conductor is sized from the largest system landed on it and not from the bar's own duty as an equipment ground. {note}
−## Where the project includes any of the listed spaces, the Contractor shall apply the additional requirements of the corresponding NEC article, which govern over the general requirements of this standard.
+# Connections and Terminations {toc}
+## Inaccessible Connections {toc}
+
+### Every connection that is buried in earth, encased in concrete, installed in a wall or above a ceiling that is not accessible, or otherwise inaccessible after construction shall be made by one of the methods indicated in the datasheet.
+
```datasheet
−label: Special Occupancy Grounding Requirements Apply
+label: Connection Methods for Inaccessible Connections
type: checkbox
options:
− - "Health care facilities (NEC Article 517)"
− - "Swimming pools, fountains, water features (NEC Article 680)"
− - "Hazardous (classified) locations (NEC Articles 500–516)"
− - "Information technology equipment rooms (NEC Article 645)"
− - "Agricultural buildings (NEC Article 547)"
− - "None of the above"
−default: "None of the above"
+ - "Exothermic welded"
+ - "Listed irreversible compression connector"
+default:
+ - "Exothermic welded"
+ - "Listed irreversible compression connector"
+constraint: any_of
```
−## In health care facilities, patient care spaces require redundant grounding and equipotential bonding per NEC Article 517, and the impedance of the equipment grounding path is limited and shall be tested.
+### An exothermic weld fuses the conductors into one piece of copper that carries fault current without a contact interface, survives in earth as long as the conductor, and needs a trained operator, a dry mold and the heat and smoke a hot-work permit covers; an irreversible compression connector listed for direct burial does the same job with a hydraulic tool and a matched die, needs no hot work and no mold inventory, and is the method a project in a finished building, in a fuel area or under a no-hot-work rule uses. Most projects accept either, and the datasheet narrows the choice where an Owner's standard or a site condition excludes one. {note}
−## Swimming pools and water features require equipotential bonding of all metal within the prescribed distance per NEC Article 680.
+### Mechanical connectors, bolted clamps and set-screw lugs shall not be installed in any location that becomes inaccessible.
−## Hazardous locations require bonding by methods that do not rely on locknuts or double-locknut-and-bushing connections per NEC 250.100, regardless of voltage.
+### Every exothermic weld shall be made with the mold and weld metal the connection system's manufacturer specifies for the conductor sizes and surfaces joined, in a clean, dry mold, on conductors cleaned to bright metal, and a weld showing porosity, slag inclusion, incomplete fill or a conductor that moves in the weld shall be cut out and remade.
+### Every compression connection shall be made with the connector, die and tool the connector's listing names for the conductors joined, with the crimp fully closed and the die's identification embossed on the connector, and a connection crimped with a die not listed for the connector shall be cut out and remade.
+
+## Accessible Connections {toc}
+
+### Every connection that remains accessible after construction shall be made by one of the methods indicated in the datasheet, and shall be made by a means NFPA 70 250.70 recognizes.
+
+```datasheet
+label: Connection Methods for Accessible Connections
+type: checkbox
+options:
+ - "Exothermic welded"
+ - "Listed irreversible compression connector"
+ - "Listed mechanical connector or clamp"
+default:
+ - "Exothermic welded"
+ - "Listed irreversible compression connector"
+ - "Listed mechanical connector or clamp"
+constraint: any_of
+```
+
+### An accessible connection can be inspected, tested and retightened, so a listed mechanical connector, a bolted clamp on a pipe or a column or a two-hole lug on a bar is acceptable and is what most accessible connections are; exothermic and compression connections are specified at accessible points where the Owner wants no connection in the system that can loosen, where the connection carries lightning current, or where a clamp would be exposed to vibration or tampering. {note}
+
+### Every connection to a ground bar, an enclosure or equipment shall be made with a listed two-hole compression lug or a listed terminal, and a single-hole lug shall be used only where the equipment provides a single tapped hole for it.
+
+### Solder shall not be used in any grounding or bonding connection, and a connection shall not depend on solder for its mechanical or electrical integrity.
+
+### Connections to a rod electrode shall be made by exothermic welding or by a listed ground rod clamp of a metal compatible with the rod, and a clamp shall be used for one conductor only unless listed for more.
+
+## Surface Preparation and Torque {toc}
+
+### Every surface a connection is made to shall be cleaned of paint, enamel, mill scale, rust, oxide and coating to bare bright metal over the full contact area before the connection is made, and where the connection joins aluminum to any other metal, a listed antioxidant compound shall be applied to the cleaned aluminum before the connection is closed.
+
+### Where a protective coating is removed to make a connection, the exposed metal around the completed connection shall be recoated with a corrosion-inhibiting coating compatible with the original finish, and a buried or embedded connection between dissimilar metals shall be coated with a listed corrosion-inhibiting compound over its entire surface.
+
+### Every bolted and mechanical grounding connection shall be tightened with a calibrated torque tool to the value the connector manufacturer publishes, or to the value ANSI/NETA ATS publishes for the bolt size where the manufacturer publishes none, and each torqued connection shall be witness-marked.
+
+### A connector between dissimilar metals shall be listed for that combination, and a copper connector or conductor shall not be placed in direct contact with galvanized steel, aluminum or a reinforcing bar in a damp, wet or buried location except through a listed bimetallic connector.
+
# Testing {toc}
−## The meaningful verification of a grounding system happens in the field after installation, not at the factory. {note}
+## Testing Organization and Report {toc}
−## The Contractor shall engage a qualified testing agency to perform the field tests below.
+### The field tests of this article shall be performed by the testing organization, with the instruments, under the safety practice and with the report that [[sync/electrical-acceptance-testing]] requires, and the grounding electrode system shall be an equipment class within that standard's acceptance test program.
−## The Contractor shall correct and re-test any item that does not meet the acceptance criteria.
+### This standard governs the method of the electrode resistance test, the value it is judged against, the scope of the continuity verification and the timing of each test, and that standard governs who performs it, the instrument calibration and the report.
−## Ground Resistance Testing {toc}
+### Every test shall be performed after the electrode system and the connections under test are complete and before the system served is energized, and the electrode resistance test shall be repeated after any electrode is added.
+## Electrode Resistance Test {toc}
+
+### The resistance to earth of each grounding electrode system shall be measured by the method indicated in the datasheet, in accordance with IEEE 81.
+
```datasheet
−label: Ground Resistance Test Method
+label: Electrode Resistance Test Method
type: select
options:
− - "Fall-of-potential (3-point) method per IEEE 81"
− - "Clamp-on (induced frequency) method"
− - "Selective / 4-point method per IEEE 81"
−default: "Fall-of-potential (3-point) method per IEEE 81"
+ - "Fall-of-potential, three-point, per IEEE 81"
+ - "Clamp-on, induced frequency"
+ - "Selective, clamp with current and potential probes"
+ - "Slope method per IEEE 81"
```
−```datasheet
−label: Maximum Acceptable Ground Resistance
−type: range
−unit: ohms
−drawing_ref: true
−options:
− min: 1
− max: 25
− setpoints: [1, 3, 5, 10, 25]
−default: 5
−```
+### The fall-of-potential test disconnects the electrode system from the service, drives two test probes out into the earth and measures the resistance directly; it is the reference method, needs the system de-energized or the electrode isolated and open ground for the probes, and is the method nearly every acceptance test uses. A clamp-on tester measures the loop resistance through the electrode and every parallel path back through the utility neutral without disconnecting anything, in minutes, and reads nothing useful on an isolated electrode with no parallel path, which makes it a maintenance method and not an acceptance method for a new electrode system. The selective method combines a clamp with probes so that one electrode of a bonded system can be measured without disconnecting it, and is the method for a site where the electrode system cannot be isolated from the utility. The slope method is a fall-of-potential variant for a large electrode system, a ring or a grid, where the probe spacing a plain fall-of-potential test needs cannot be had on the site. {note}
−### The resistance to earth of the grounding electrode system shall be measured after installation and before the system is placed in service, in accordance with IEEE 81 and ANSI/NETA ATS.
+### Where the fall-of-potential or slope method is selected, the electrode system shall be isolated from the utility neutral and from every other grounded system during the test, the current probe shall be placed at a distance not less than five times the longest dimension of the electrode system, and readings shall be taken at not fewer than three potential probe positions to confirm that the measurement lies on the flat portion of the curve.
−### The test method shall be appropriate to the electrode configuration and site conditions.
+### The electrode resistance test shall be performed with the soil at its natural moisture, not during rain and not within 48 hours after rainfall that wets the soil to the depth of the electrodes, and the date, the weather of the preceding 48 hours, the soil condition and the air temperature shall be recorded with each reading.
−### The fall-of-potential method is the reference method and shall be used for acceptance testing of the grounding electrode system where the electrode can be temporarily isolated and where space permits placement of test electrodes.
+### The test shall be performed on the complete electrode system and in addition on each rod, plate or electrolytic electrode individually before it is bonded into the system, and the individual readings shall be recorded.
−### The clamp-on method may be used for periodic verification of installed electrodes that have a parallel return path, but it shall not be used as the sole acceptance test of an isolated electrode because it requires a parallel path to produce a reading.
+### A measured resistance exceeding the value in the Resistance to Earth Target article is a deficiency, to be corrected as that article requires.
−### The maximum acceptable ground resistance shall be [[drawing: as indicated on the contract documents]].
+### A resistance measured the day after a storm is the lowest the system will ever read and says nothing about August. The individual rod readings are recorded because a system that meets the target with one rod carrying it has no margin when that rod corrodes, and because the readings are the only way to find a rod that was driven into a void. {note}
−### Where a measured value exceeds the acceptance criterion, the Contractor shall add electrodes, extend the ground ring, or apply ground-enhancement measures and re-test until the criterion is met.
+## Bonding and Continuity Verification {toc}
−### A value of 5 Ω is a common target for commercial buildings and provides margin below the 25-Ω code threshold; facilities with sensitive electronic systems, data centers, and critical operations frequently require lower values that the Engineer shall set. {note}
+### The continuity and the resistance of the bonding and equipment grounding paths indicated in the datasheet shall be verified with a low-resistance ohmmeter applying not less than 10 A direct current, and every measured path shall read 0.1 Ω or less across each connection and 1 Ω or less from the point tested to the service or derived-system grounding point.
−## Continuity and Bonding Verification {toc}
−
```datasheet
−label: Bonding Continuity Verification Scope
+label: Bonding and Continuity Verification Scope
type: checkbox
options:
− - "Service equipment bonding jumpers"
− - "Each separately derived system bonding"
− - "Metal piping and structural steel bonding"
+ - "Main bonding jumper and service raceway bonding"
+ - "System bonding jumper and grounding electrode conductor of each separately derived system"
+ - "Piping and structural metal bonding jumpers"
- "Intersystem bonding termination"
− - "Equipment ground bus in each panelboard"
− - "Representative branch circuit equipment grounding paths"
−default: "Service equipment bonding jumpers"
+ - "Ground bar bonding conductors"
+ - "Equipment grounding path from representative outlets and equipment to the source"
+ - "Isolated-ground circuits from each receptacle to the source grounding point"
+ - "Lightning protection and telecommunications common bonds"
+default:
+ - "Main bonding jumper and service raceway bonding"
+ - "System bonding jumper and grounding electrode conductor of each separately derived system"
+ - "Piping and structural metal bonding jumpers"
+ - "Intersystem bonding termination"
+ - "Ground bar bonding conductors"
+ - "Equipment grounding path from representative outlets and equipment to the source"
+constraint: all_of
```
−### The Contractor shall verify electrical continuity of the equipment grounding system from representative points of utilization back to the service or derived-system grounding point.
+### Where the equipment grounding path from representative outlets and equipment is selected, not fewer than one outlet or item of equipment on each branch circuit panelboard and every item of equipment rated 100 A or more shall be tested, and where any tested path fails, every path on that panelboard shall be tested.
−### The continuity of bonding jumpers at service equipment, around water meters and insulating fittings, and across expansion or vibration fittings in raceway runs shall be confirmed.
+### Every patient care space, where that occupancy is selected, shall in addition receive the grounding system test NFPA 99 requires, with the voltage and the impedance between the reference grounding point and every exposed conductive surface and receptacle grounding contact measured and recorded.
−## Connection Integrity {toc}
+### The line-to-ground fault current a short-circuit study under [[sync/short-circuit-study]] calculates exists only if the bonding path it assumes exists, and the continuity test is what proves the path. A connection that reads 0.5 Ω is one that heats, and a path that reads 3 Ω is one on which a 20 A breaker sees a fault as a 40 A load. {note}
−### Accessible mechanical grounding connections shall be checked for tightness against the manufacturer's torque specifications using a calibrated torque tool.
+## Objectionable Current {toc}
−### Exothermic welded connections shall be inspected visually for full fusion, absence of porosity, and proper conductor coverage.
+### After energization and with the building under normal load, the current on the grounding electrode conductor, on the main bonding jumper, on the bonding jumper of each separately derived system and on the equipment grounding conductor of each feeder shall be measured with a clamp-on ammeter and recorded, and any reading exceeding 1 A, or any reading on a feeder equipment grounding conductor exceeding 10% of the neutral current of that feeder, shall be investigated.
−### A connection that can be moved or that shows incomplete fusion shall be cut out and remade.
+### Where the investigation finds a neutral-to-ground connection downstream of the service or of a system bonding jumper, a shared neutral between circuits on different equipment grounding paths, or a grounded conductor landed on a ground bar, the Contractor shall correct it and shall repeat the measurement.
−## Objectionable Current Check {toc}
+## Deficiencies and Retesting {toc}
−### The Contractor shall verify, with the building under normal load, that grounding conductors and bonding jumpers do not carry objectionable current per NEC 250.6.
+### A connection that cannot be moved by hand, that reads within the continuity limits and that shows the torque witness mark or a sound weld is accepted; a connection that fails any of these shall be remade and retested.
−### Measurable current on a grounding electrode conductor or on an equipment grounding conductor under normal operation indicates an improper neutral-to-ground connection or a wiring error, which the Contractor shall locate and correct.
+### The cost of correcting a deficiency found under this article and of every repeated test shall be borne by the Contractor, except for the additional electrodes the Resistance to Earth Target article assigns to the Owner.
−## Test Reporting {toc}
+### Where the Contractor and the testing organization disagree whether a result is a deficiency, the Engineer of Record shall make the determination.
−### All test results shall be recorded on the testing agency's report forms, including the test method, instrument identification and calibration date, ambient conditions, measured values, acceptance criteria, pass/fail determination, and the corrective action taken for any failed item.
+# Installation {toc}
−### Reports shall be included in the closeout submittals.
+## Sequencing and Concealment {toc}
−# Installation {toc}
+### The concrete-encased electrode and its tail or stub shall be installed, inspected and protected before the footing concrete is placed, and the Contractor shall notify the Engineer of Record not less than two working days before each pour that contains an electrode.
−## Coordination and Sequencing {toc}
+### Trenches for ground rings, buried conductors and rod electrodes shall be left open, or the connections left exposed, until the Inspection Before Concealment article has been satisfied.
−### The Contractor shall sequence grounding work so that no portion of the grounding electrode system is concealed before it is inspected.
+### Grounding connections at equipment shall be made before the equipment is energized, and no equipment shall be energized with its equipment grounding conductor or its bonding jumper unterminated.
−### The connection tail for the concrete-encased electrode shall be installed and protected before foundation concrete is placed.
+## Electrode Installation and Backfill {toc}
−### Ground ring and electrode trenches shall be left open, or the connections left accessible, until inspected and released by the Authority Having Jurisdiction.
+### Rod electrodes shall be installed by driving with a driver that does not mushroom the head or strip the coating, and not by excavating and backfilling, except where rock makes driving impossible and the angled or trenched alternatives of NFPA 70 250.53(G) are used, with the alternative recorded on the electrode layout.
−## Routing {toc}
+### Rod electrodes shall be installed not less than 2 ft from the foundation wall, outside the drip line of the roof where practicable, and clear of every other underground utility by the separation its owner requires, and the top of each rod shall be not less than 12 in. below finished grade unless it is in a test well.
−### Grounding electrode conductors and bonding jumpers shall be routed as directly and as short as practical.
+### Trenches for ground rings and buried grounding conductors shall be backfilled with the excavated native soil free of rock, debris, cinders, slag and construction waste, placed and compacted so that the conductor is in full contact with soil, and ground enhancement material where used shall be placed around the electrode before the native soil.
−### Sharp bends shall be avoided; the conductor shall not be bent to a radius smaller than that which would damage the conductor or its insulation.
+### Buried grounding conductors shall be installed at a depth of not less than 18 in., except that the ground ring shall be at the depth the datasheet requires, and a buried conductor that crosses a road, a utility or a structure footing shall be sleeved only where the sleeve is nonmetallic.
−### Conductors shall be supported and protected so that they are not subject to physical damage or to use as a handhold or support.
+## Test Wells {toc}
−## Electrode Installation {toc}
+### Test wells shall be provided as indicated in the datasheet, and each shall be a precast concrete, polymer concrete or heavy-duty polymer box with a bolted cover marked GROUND, set flush with grade over the electrode, with the connection to the electrode accessible inside it.
−### Driven electrodes shall be installed by driving, not by excavating and backfilling, except where rock or refusal makes driving impossible and the oblique or buried alternatives of NEC 250.53(G) are used.
+```datasheet
+label: Ground Rod Test Wells
+type: radio
+options:
+ - "None"
+ - "At the electrode the resistance test is made on"
+ - "At every rod electrode"
+```
−### Electrodes shall be installed clear of the building footprint and clear of other utilities by the spacing required by the utility owners.
+### A test well lets the resistance test be repeated over the life of the building without excavating, and lets a clamp-on tester be put around the conductor to the electrode. No test well is the arrangement of a building whose electrodes are the footing steel and whose rods are never expected to be retested; a well at the electrode the acceptance test is made on gives the maintenance program one place to repeat it; a well at every rod is the design of a communications site, a data center or a substation yard where the rods are retested on a schedule and the one that has corroded must be found. {note}
−## Backfill {toc}
+### Where the ground ring is the electrode the test is made on, a test well shall be installed over a point on the ring where the conductor to the service is connected, and the connection in the well shall be exothermic welded or a listed irreversible compression connection with a test link.
−### Trenches for ground rings and buried conductors shall be backfilled with the excavated native soil, compacted, and free of rock, debris, and corrosive fill in contact with the conductor.
+## Routing and Support of Conductors {toc}
−### Where ground-enhancement material is specified, it shall be installed around the electrode in accordance with the manufacturer's instructions before backfill.
+### Grounding electrode conductors, bonding jumpers and ground bar bonding conductors shall be routed as directly as the structure permits, shall be supported at intervals not exceeding 5 ft and within 12 in. of every termination, shall not be used as a support or a handhold for anything, and shall be protected from physical damage where they are exposed to it.
−## Protection During Construction {toc}
+### A grounding or bonding conductor shall not be run through a metal sleeve, a metal plate or the wall of a ferrous enclosure unless it is bonded to the sleeve, plate or enclosure at that point, or unless the opening is slotted or fitted with a nonmetallic bushing so that the conductor is not encircled by ferrous metal.
−### Grounding conductors and connections left exposed during construction shall be protected from damage by other trades.
+### Temporary grounding installed for construction power or for the protection of workers shall be removed when it is no longer needed unless it is part of the permanent installation, and no temporary ground shall be left in place where it creates a parallel path the permanent design does not intend.
−### Temporary grounding installed for construction power shall be removed where it is not part of the permanent installation, and shall not be left to create unintended parallel paths.
+# Identification {toc}
−# Identification and Labeling {toc}
+## The grounding system shall be identified at the points indicated in the datasheet, with labels of the materials and lettering [[sync/electrical-identification]] requires.
```datasheet
−label: Grounding System Labeling
+label: Grounding System Labels
type: checkbox
options:
− - "Grounding electrode conductor connection points"
+ - "Grounding electrode conductor at each end and at each connection to an electrode"
+ - "Main bonding jumper and each system bonding jumper"
- "Intersystem bonding termination"
− - "Isolated ground receptacles (orange triangle)"
− - "Ground bars in electrical and telecom rooms"
− - "Main bonding jumper / system bonding jumper locations"
−default: "Intersystem bonding termination"
+ - "Each ground bar, with the systems landed on it"
+ - "Each test well cover"
+ - "Common bond to the lightning protection system"
+ - "Common bond to the telecommunications bonding conductor"
+default:
+ - "Grounding electrode conductor at each end and at each connection to an electrode"
+ - "Main bonding jumper and each system bonding jumper"
+ - "Intersystem bonding termination"
+ - "Each ground bar, with the systems landed on it"
+ - "Each test well cover"
+constraint: all_of
```
−## Wire-type equipment grounding conductors shall be identified by green or green-with-yellow-stripe insulation, or shall be bare, in accordance with NEC 250.119.
+## The intersystem bonding termination shall be labeled to identify it as the bonding point for communications systems, and the label shall remain legible and visible after the service equipment and its surroundings are finished.
−## Grounded (neutral) conductors shall be identified white or gray and shall not be confused with equipment grounding conductors.
+## Each ground bar shall carry a label naming the bar and listing the grounding electrode conductor, the derived systems and the bonding conductors landed on it, and each conductor landed on the bar shall carry a tag naming its origin.
−## The grounding electrode conductor and its connection points shall be labeled where the label aids future maintenance, for example at the connection to a concrete-encased electrode or at a ground ring access point.
+## Every grounding and bonding conductor that is bare or whose insulation is not green shall be identified green at each termination and at every accessible point, and the grounded conductor shall be identified white or gray and never green.
−## The intersystem bonding termination shall be labeled to identify it as the point for bonding other systems.
+## A ground bar with a dozen unlabeled conductors on it cannot be tested, because the technician cannot tell which conductor is the transformer tap and which is the door bond, and cannot be safely worked on, because a lifted conductor can be the only ground of a live derived system. {note}
−## Isolated ground receptacles shall carry the orange triangle identification required by NEC 406.3(E), and isolated ground circuits shall be identified at the panelboard.
−
# Delivery, Storage, and Handling {toc}
−## Grounding and bonding materials shall be delivered in the manufacturer's original packaging with listing marks intact.
+## Grounding and bonding materials shall be delivered in the manufacturer's original packaging with the listing marks and the connector size and conductor range markings legible.
−## Conductors and connectors shall be stored indoors in a clean, dry location and protected from corrosive atmospheres until installed.
+## Exothermic molds, weld metal and starting material shall be stored in a dry, heated space, a cartridge that has been wet shall not be used, and a mold that is cracked, eroded or carbon-fouled beyond the manufacturer's stated life shall be discarded.
−## Ground rods shall be stored so that the bonding coating and the driving end are not damaged.
+## Rod electrodes shall be stored off the ground, with the driving end and the copper bonding protected from damage, and a rod whose bonding is nicked to the steel over more than 1 in. of length shall not be installed.
−## Exothermic weld molds and weld material shall be stored dry, because moisture in the mold or charge produces porous, defective welds.
+## Bare copper conductor shall be stored on reels or in coils off the ground, protected from contact with concrete, acid, fertilizer and road salt, and shall be installed clean.
# Warranty {toc}
+## The Contractor shall warrant the grounding and bonding installation, including every connection and the measured resistance to earth of the electrode system, against defects in materials and workmanship for the period indicated in the datasheet from the date of substantial completion.
+
```datasheet
label: Installation Warranty Period
−type: select
+type: range
+unit: years
options:
− - "1 year from substantial completion"
− - "2 years from substantial completion"
−default: "1 year from substantial completion"
+ min: 1
+ max: 5
+ setpoints: [1, 2, 3, 5]
+default: 1
+constraint: min
```
−## Grounding and bonding products that carry a manufacturer warranty against defects in materials and workmanship shall be warranted to the Owner.
+## Where the measured resistance to earth at acceptance was within 20% of the value in the datasheet, the Contractor shall repeat the electrode resistance test once during the warranty period in the driest month of the year at no cost to the Owner, and where the repeated measurement exceeds the value in the datasheet, the Contractor shall add electrodes under the warranty until it does not.
−## The Contractor shall warrant the installation, including all connections and the achievement of the specified ground resistance, for the project warranty period.
+## A connection found loose, corroded or open during the warranty period shall be remade at the Contractor's cost, together with any equipment damage the Engineer of Record attributes to the defective connection, and the remade connection shall carry a fresh warranty of the full period from the date it is remade.
−## Where the achieved ground resistance is marginal relative to the acceptance criterion, the Engineer may require a re-test during the warranty period to confirm that seasonal soil changes have not raised the resistance above the acceptance value.
+## The warranty on the grounding products themselves shall be the manufacturer's standard warranty, assigned to the Owner, and shall not reduce the Contractor's installation warranty.