Grounding and Bonding for Electrical Systems
Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
Showing changes from Rev 5
to Rev 6
in Grounding and Bonding for Electrical Systems.
---
title: Grounding and Bonding for Electrical Systems
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## Grounding and bonding is a coordinated system that touches nearly every other electrical scope rather than a single product. {note}
−## 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. {note}
+## 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.
## 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}
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## 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.
−## 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. {note}
+## 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.
## Required Electrodes {toc}
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### Every electrode listed that exists at the building shall be bonded into the grounding electrode system.
−### 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. {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.
### Concrete-encased electrode {toc}
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#### 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).
−#### A single rod, pipe, or plate electrode that does not have a resistance to earth of 25 ohms or less shall be supplemented by one additional electrode, in accordance with NEC 250.53(A)(2).
+#### 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).
#### Where two rods are used, they shall be spaced at least 6 ft apart.
#### Spacing of at least one rod length is recommended because closely spaced rods share the same volume of soil and add little. {note}
−#### The 25-ohm threshold is a code minimum, not a performance target; the project value shall be taken from the testing requirements of this standard. {note}
+#### 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.
#### 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}
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### Because grounding electrode conductors so frequently run to buried or near-earth electrodes, copper is the practical default. {note}
−## Sizing {toc}
+## Grounding Electrode Conductor Sizing {toc}
```datasheet
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### 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}
−## Sizing {toc}
+## Equipment Grounding Conductor Sizing {toc}
```datasheet
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### The Contractor shall confirm for each bonding jumper whether it is on the supply side or load side and size it accordingly.
−### Supply-side jumpers must carry fault current with no upstream protection and are therefore sized more conservatively. {note}
+### Supply-side jumpers must carry fault current with no upstream protection and are therefore sized more conservatively.
## Bonding at Service Equipment {toc}
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### Connectors not so listed shall not be buried or encased.
−# Materials {toc}
+# Conductors {toc}
−## Conductors {toc}
+## 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.
−### 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.
+## Bare grounding conductors used as electrodes or buried shall be soft-drawn copper.
−### Bare grounding conductors used as electrodes or buried shall be soft-drawn copper.
+# Ground Bars and Busbars {toc}
−## Ground Bars and Busbars {toc}
+## Ground bars and busbars shall be copper conforming to ASTM B187.
−### Ground bars and busbars shall be copper conforming to ASTM B187.
+## Tin plating shall be provided where specified to reduce contact-surface oxidation and to ease future re-termination.
−### Tin plating shall be provided where specified to reduce contact-surface oxidation and to ease future re-termination.
+# Ground Rods {toc}
−## Ground Rods {toc}
+## Ground rod electrodes shall conform to NEMA GR 1 and shall be listed to UL 467.
−### Ground rod electrodes shall conform to NEMA GR 1 and shall be listed to UL 467.
+## 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.
−### 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.
+# Connectors and Clamps {toc}
−## Connectors and Clamps {toc}
+## 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.
−### 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.
+## Connectors of dissimilar metal to the conductor or the contacted surface shall not be used in damp, wet, or buried locations.
−### Connectors of dissimilar metal to the conductor or the contacted surface shall not be used in damp, wet, or buried locations.
−
# Isolated and Insulated Grounding {toc}
## 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}
−```datasheet
−label: Isolated Ground Receptacles
−type: radio
−options:
− - "Not used"
− - "Provided at designated sensitive-equipment locations"
−default: "Not used"
−```
−
## 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}
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## The Engineer should confirm that the connected equipment actually requires an isolated ground before specifying it.
+```datasheet
+label: Isolated Ground Receptacles
+type: radio
+options:
+ - "Not used"
+ - "Provided at designated sensitive-equipment locations"
+default: "Not used"
+```
+
## Where isolated ground receptacles are installed, they shall be identified by the orange triangle marking required by NEC 406.3(E).
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## Certain occupancies impose grounding and bonding requirements beyond the general rules of NEC Article 250. {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.
+
```datasheet
label: Special Occupancy Grounding Requirements Apply
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```
−## 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.
−
## 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.
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### 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.
−### A value of 5 ohms is a common target for commercial buildings and provides margin below the 25-ohm code threshold; facilities with sensitive electronic systems, data centers, and critical operations frequently require lower values that the Engineer shall set. {note}
+### 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}
## Continuity and Bonding Verification {toc}
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## 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.