Low Voltage Switchboards
Remade from scratch to the authoring rules: defaults asserted only where four of five projects would choose them, and scope boundaries matched to the neighboring standards
Showing changes from Rev 7
to Rev 8
in Low Voltage Switchboards.
---
title: Low Voltage Switchboards
category: Electrical / Power Distribution Equipment
−toc_depth: 3
description: >
− When to use: Dead-front, free-standing low voltage distribution switchboards rated 600V and below, built to UL 891 and NEMA PB 2, with group-mounted molded-case or insulated-case circuit breakers (fixed-mounted or individually drawout). Covers service entrance and downstream distribution boards for commercial, institutional, and industrial facilities. Not intended for: Metal-enclosed power circuit breaker switchgear (see [[sync/low-voltage-switchgear]]), branch-circuit panelboards (see [[sync/panelboards]]), motor control centers (see [[sync/motor-control-centers]]), or medium voltage equipment above 600V (see [[sync/medium-voltage-switchgear]]).
+ When to use: Dead-front, floor-standing distribution switchboards rated 1000 V and below, listed to UL 891 and built to NEMA PB 2, in which molded-case or insulated-case circuit breakers, fusible switches, or bolted-pressure switches are group-mounted or individually mounted on a common bus, whether installed as service equipment or downstream of a transformer, switchgear, or another switchboard. Covers the ratings, the interrupting rating basis, the main and feeder devices and their trip units, the bus, the structure and enclosure, arc-flash mitigation, the service entrance, surge protection, metering and communications provisions built into the assembly, identification, factory and field testing, installation, warranty, and spares, for three-phase and single-phase AC systems in indoor and outdoor locations.
+
+ Not intended for: metal-enclosed switchgear listed to UL 1558 and IEEE C37.20.1, built around IEEE C37.13 power devices on withdrawable rails ([[sync/low-voltage-switchgear]]); cabinet-mounted UL 67 panelboards that subdivide a feeder into branch circuits ([[sync/panelboards]]); UL 845 lineups of starter cells on a common vertical bus ([[sync/motor-control-centers]]); anything above 1000 V ([[sync/medium-voltage-switchgear]]); the arrangement, throat, and coordinated ratings of a unit substation that a switchboard is shipped in as its secondary section ([[sync/secondary-unit-substations]], which invokes this standard for that section's construction); the utility point of delivery, the conductors from it, the meter socket, and the utility's metering requirements ahead of the main device ([[sync/electrical-service-entrance]]); the busway run itself, its hangers, and its joints ([[sync/busway]]); the trough of a wireway or auxiliary gutter adjoining the switchboard ([[sync/wireways-and-auxiliary-gutters]]); the strike termination network and down conductors ([[sync/lightning-protection]]); UL 508A panels for process automation ([[sync/industrial-control-panels]]); the surge protective device as a product ([[sync/surge-protective-devices]]); the meters themselves ([[sync/electrical-power-monitoring]]); DC switchboards; switchboards in hazardous classified locations; and the short-circuit, coordination, and arc-flash studies that establish the ratings and settings the switchboard is ordered to ([[sync/short-circuit-study]], [[sync/protective-coordination-study]], [[sync/arc-flash-study]]).
---
# Scope {toc}
−## This specification covers dead-front, free-standing distribution switchboards rated 600V and below, constructed and listed to UL 891 (Switchboards) and NEMA PB 2. {note}
−## Switchboards covered by this standard use group-mounted molded-case circuit breakers (MCCBs) or insulated-case circuit breakers (ICCBs) as the primary overcurrent protective devices. {note}
−## Devices may be fixed-mounted or individually drawout depending on project requirements.
+## This standard governs the switchboard as a listed assembly: the structure and its sections, the bus and its supports, the main and feeder devices and their mounting, the compartments built into the structure for utility metering, surge protection, and power monitoring, and the field work that puts the switchboard into service. {note}
−## For lighting and appliance branch-circuit panelboards or distribution panelboards, see [[sync/panelboards]]. {note}
−## For motor starter assemblies, see [[sync/motor-control-centers]]. {note}
−## Grounding and bonding shall be per [[sync/grounding-and-bonding]].
−## Feeders and branch circuit conductors entering and leaving the switchboard shall comply with [[sync/conductors-and-cables]] and [[sync/raceways-and-conduit]].
+## A switchboard is a large single panel, frame, or assembly of panels on which switches, overcurrent devices, buses, and instruments are mounted, accessible from the front or from the front and rear, and not intended to be installed in a cabinet; dead-front construction leaves no energized part exposed on the operating face. It is the equipment at the head of a low-voltage distribution system, taking the service or a transformer secondary and dividing it into the feeders that serve panelboards, motor control centers, and large loads. {note}
−## Switchboards differ from low voltage switchgear in construction, testing standard, and breaker type. {note}
+## Four assembly standards divide low-voltage distribution equipment by construction and listing, and this one is the UL 891 dead-front switchboard. [[sync/low-voltage-switchgear]] is the assembly listed to UL 1558 and IEEE C37.20.1, built around IEEE C37.13 power devices on withdrawable rails in individual compartments; [[sync/panelboards]] is the UL 67 cabinet whose branch devices subdivide one feeder; [[sync/motor-control-centers]] is the UL 845 lineup of starter cells on a shared vertical bus; [[sync/medium-voltage-switchgear]] is anything above 1000 V. {note}
−## Switchgear (UL 1558, IEEE C37.20.1) uses individually compartmented drawout power circuit breakers and is typically front-and-rear accessible. {note}
+## The switchboard is one listed product. Its short-circuit current rating, its seismic certification, and its arc-flash characteristics are properties of the whole assembly in the configuration shipped, and a device, a bus modification, or a compartment added outside that listing removes the switchboard from the condition under which it was rated. {note}
−## Switchboards (UL 891) use group-mounted MCCB/ICCB devices in a more compact, often front-accessible enclosure and are tested as an assembly to UL 891 short-circuit current ratings. {note}
+## The following are governed elsewhere and are outside this standard: {note}
−## For power circuit breaker switchgear, see [[sync/low-voltage-switchgear]]. {note}
+- the service point, the service conductors, the meter socket, and the serving utility's metering requirements, under [[sync/electrical-service-entrance]]
+- the feeders that leave the switchboard and the conductors that enter it, and their terminations, under [[sync/conductors-and-cables]]
+- the raceways entering the structure, under [[sync/raceways-and-conduit]]
+- the busway run, its supports, and its joints, under [[sync/busway]]
+- the wireway or auxiliary gutter trough that adjoins the structure, under [[sync/wireways-and-auxiliary-gutters]]
+- the grounding electrode system, the equipment grounding conductors, and the bonding of a separately derived system, under [[sync/grounding-and-bonding]]
+- the surge protective device as a product, its ratings, its protection modes, and its lead length, under [[sync/surge-protective-devices]]
+- the meters, their accuracy class, their current transformers, and the monitoring system they report to, under [[sync/electrical-power-monitoring]]
+- the transformer feeding the switchboard, under [[sync/medium-voltage-transformers]] or [[sync/low-voltage-dry-type-transformers]]
+- the automatic transfer switch on either side of the switchboard, under [[sync/automatic-transfer-switches]]
+- the short-circuit, coordination, and arc-flash studies, under [[sync/short-circuit-study]], [[sync/protective-coordination-study]], and [[sync/arc-flash-study]]
+- the room the switchboard occupies, under [[sync/electrical-rooms]]
+- the housekeeping pad the switchboard stands on, under [[sync/concrete-pads]]
+## Switchboards shall comply with NEMA PB 2 and shall be listed and labeled to UL 891 by a Nationally Recognized Testing Laboratory.
+
+## The location and orientation of each switchboard shall be as indicated on [[drawing: the electrical plans]].
+
+## Where a value stated on the one-line diagram for a particular switchboard differs from the datasheet selection under this standard, the one-line diagram shall govern for that switchboard.
+
# Referenced Standards {toc}
−## Equipment and installation shall comply with the latest edition of the following.
+## Equipment, 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 serving utility's requirements, 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 |
|----------|-------|
| UL 891 | Switchboards |
| UL 489 | Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures |
+| UL 98 | Enclosed and Dead-Front Switches |
+| UL 977 | Fused Power-Circuit Devices |
| UL 869A | Reference Standard for Service Equipment |
+| UL 1053 | Ground-Fault Sensing and Relaying Equipment |
+| UL 1449 | Surge Protective Devices |
+| UL 50 | Enclosures for Electrical Equipment, Non-Environmental Considerations |
+| UL 50E | Enclosures for Electrical Equipment, Environmental Considerations |
| NEMA PB 2 | Deadfront Distribution Switchboards |
| NEMA PB 2.1 | General Instructions for Proper Handling, Installation, Operation, and Maintenance of Deadfront Distribution Switchboards Rated 600 Volts or Less |
+| NEMA AB 1 | Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures |
+| NEMA 250 | Enclosures for Electrical Equipment (1000 Volts Maximum) |
| IEEE C37.13 | Low-Voltage AC Power Circuit Breakers Used in Enclosures |
| IEEE C37.20.7 | Guide for Testing Switchgear Rated Up to 52 kV for Internal Arcing Faults |
| IEEE C57.13 | Requirements for Instrument Transformers |
| IEEE 1584 | Guide for Performing Arc-Flash Hazard Calculations |
−| IEEE 519 | Recommended Practice and Requirements for Harmonic Control in Electric Power Systems |
−| NFPA 70 | National Electrical Code |
+| NFPA 70 | National Electrical Code (Articles 110, 215, 230, 240, 250, 312, 408, 700, 701, and 708) |
| NFPA 70E | Standard for Electrical Safety in the Workplace |
−| NEMA 250 | Enclosures for Electrical Equipment (1000 Volts Maximum) |
−| NETA ATS | Acceptance Testing Specifications for Electrical Power Equipment and Systems |
−| IBC | International Building Code |
−| ASCE 7 | Minimum Design Loads and Associated Criteria for Buildings and Other Structures |
−| ICC ES AC156 | Acceptance Criteria for Seismic Certification by Shake-Table Testing |
−| ASHRAE 90.1 | Energy Standard for Buildings (submetering requirements) |
+| ASTM B187 | Copper, Bus Bar, Rod, and Shapes and General Purpose Rod, Bar, and Shapes |
+| ASTM B317 | Aluminum-Alloy Extruded Bar, Rod, Tube, Pipe, Structural Profiles, and Profiles for Electrical Purposes (Bus Conductor) |
+| ANSI/NETA ATS | Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems |
+| ASCE 7 | Minimum Design Loads and Associated Criteria for Buildings and Other Structures (Chapter 13) |
+| ICC-ES AC156 | Acceptance Criteria for Seismic Certification by Shake-Table Testing of Nonstructural Components |
−## Where conflicts exist between referenced standards, the more stringent requirement shall govern unless otherwise directed by the Engineer of Record.
−
# Submittals {toc}
## Action Submittals {toc}
−### Contractor shall submit the following for review prior to fabrication:
+### The Contractor shall submit the following for review before any switchboard is released for manufacture:
−- Shop drawings showing front and side elevations with overall dimensions, section arrangement, and shipping splits
−- Single line diagram indicating bus rating, short-circuit current rating, breaker frame sizes, and trip ratings
−- Bill of materials listing all major components by type and rating
−- Time-current coordination curves for all protective devices including ground fault elements
−- Control schematic and wiring diagrams for any control, metering, and communication circuits
−- Bus bracing and short-circuit withstand calculations or UL 891 series test references
−- Heat loss data per section for ventilation and HVAC coordination
−- Seismic certification documentation, where required
−- Conduit entry diagrams showing top and bottom entry zones
+- shop drawings for each switchboard giving the front and side elevations, the section widths, depths, and heights, the shipping splits, the weight and the lifting provisions of each shipping section, the conduit entry areas, and the anchorage pattern
+- an assembly one-line diagram showing the incoming connection, the main device, the bus with its continuous and short-circuit ratings, the neutral and ground bus, and every feeder device by its designation
+- a device schedule giving the frame size, the trip rating, the trip unit type, the interrupting rating, and the accessories of every device, and every spare and space position
+- the bus material, plating, and sizing basis, with the bus bracing rating
+- the assembly short-circuit current rating and the basis on which it is established, and where the basis is a series rating, the tested combination and the upstream device on which each rating depends
+- the heat release of each section at rated load, for coordination of the room ventilation
+- the seismic certification for the switchboard as furnished, where the datasheet requires one
+- product data for every device, for the metering and communications components, and for the surge protective device, where either is furnished within the assembly
+- schematic and wiring diagrams for the control, metering, ground-fault, and communications circuits
+- the nameplate schedule listing the text to appear on each assembly and device nameplate
```datasheet
−label: Submittal Documentation
+label: Action Submittals
type: checkbox
options:
− - "Shop drawings (front and side elevations, sections)"
− - "Single line diagram with ratings"
− - "Bill of materials"
− - "Time-current coordination curves"
− - "Control schematics and wiring diagrams"
− - "Bus bracing and short-circuit calculations"
− - "Heat loss data per section"
− - "Seismic certification (IBC/ASCE 7)"
− - "Conduit entry diagrams"
− - "Catalog cut sheets for all protective devices and meters"
+ - "Shop drawings"
+ - "Assembly one-line diagram"
+ - "Device schedule"
+ - "Bus data and bracing rating"
+ - "Short-circuit current rating basis and series-rated combinations"
+ - "Heat release per section"
+ - "Seismic certification"
+ - "Device, metering, and surge protective device product data"
+ - "Schematic and wiring diagrams"
+ - "Nameplate schedule"
default:
− - "Shop drawings (front and side elevations, sections)"
− - "Single line diagram with ratings"
− - "Bill of materials"
− - "Time-current coordination curves"
− - "Control schematics and wiring diagrams"
− - "Bus bracing and short-circuit calculations"
− - "Heat loss data per section"
− - "Conduit entry diagrams"
− - "Catalog cut sheets for all protective devices and meters"
+ - "Shop drawings"
+ - "Assembly one-line diagram"
+ - "Device schedule"
+ - "Bus data and bracing rating"
+ - "Short-circuit current rating basis and series-rated combinations"
+ - "Heat release per section"
+ - "Device, metering, and surge protective device product data"
+ - "Schematic and wiring diagrams"
+ - "Nameplate schedule"
```
+### A switchboard shall not be released for manufacture until the action submittals covering it have been reviewed and returned.
+
+### The short-circuit current rating is the submittal item that most often comes back wrong, because a catalog rating is the rating of the highest-rated device the structure accepts, and the rating that applies to the switchboard is the lowest rating among the bus bracing, the main device, and every feeder device actually installed, or the series-rated combination that covers them. {note}
+
+## Informational Submittals {toc}
+
+### The Contractor shall submit the following with or before the action submittals:
+
+- the manufacturer's qualification statement required under Quality Assurance
+- the qualifications of the firm and the technicians who will perform field acceptance testing
+- the factory test procedure, where the datasheet selects witnessed factory testing
+- the time-current characteristic curves and the setting ranges of every trip unit, relay, and fuse furnished, for use in the study performed under [[sync/protective-coordination-study]]
+- the manufacturer's published derating factors applied for ambient temperature and altitude, where either exceeds the rating basis of the listing
+- the serving utility's written acceptance of the metering compartment arrangement, where the switchboard is service equipment
+
+```datasheet
+label: Informational Submittals
+type: checkbox
+options:
+ - "Manufacturer's qualification statement"
+ - "Field testing firm and technician qualifications"
+ - "Factory test procedure"
+ - "Trip unit and fuse characteristic data for the coordination study"
+ - "Ambient and altitude derating factors"
+ - "Utility acceptance of the metering compartment"
+default:
+ - "Manufacturer's qualification statement"
+ - "Field testing firm and technician qualifications"
+ - "Trip unit and fuse characteristic data for the coordination study"
+```
+
## Closeout Submittals {toc}
−### Contractor shall provide at substantial completion:
+### The Contractor shall submit the following before any switchboard is accepted:
−- Operation and maintenance manuals, bound with table of contents and indexed by section
−- As-built shop drawings reflecting field modifications
−- Factory production test reports
−- Field acceptance test reports per NETA ATS
−- Arc flash incident energy analysis and labels
−- Warranty documentation
−- Spare parts inventory with reorder information
+- record drawings reflecting every field change to the device arrangement, the wiring, and the network addressing
+- the certified factory test report
+- the field acceptance test report for each switchboard, giving every measured value, the acceptance criterion applied, and the tester's determination
+- the ground-fault protection performance test record required by NFPA 70 230.95(C), where ground-fault protection of equipment is furnished
+- the arc energy reduction documentation and performance test record required by NFPA 70 240.87, where a device rated 1200 A or more is furnished
+- the final settings of every adjustable trip unit and relay, as commissioned
+- the network address list and the point list for every networked device, where a network is furnished
+- operation and maintenance data covering the structure, the bus, each device, and the inspection and re-torque intervals of NEMA PB 2.1
+- the warranty certificate identifying each switchboard by designation and the warranty commencement date
+- a signed receipt from the Owner for the spare parts and keys delivered
```datasheet
−label: Required Closeout Submittals
+label: Closeout Submittals
type: checkbox
options:
− - "Operation and maintenance manuals"
− - "As-built shop drawings"
− - "Factory production test reports"
− - "Field acceptance test reports per NETA ATS"
− - "Arc flash incident energy analysis and labels"
− - "Warranty documentation"
− - "Spare parts inventory with reorder information"
+ - "Record drawings"
+ - "Certified factory test report"
+ - "Field acceptance test reports"
+ - "Ground-fault protection performance test record"
+ - "Arc energy reduction documentation and test record"
+ - "Final trip unit and relay settings"
+ - "Network address and point list"
+ - "Operation and maintenance data"
+ - "Warranty certificate"
+ - "Spare parts and keys receipt"
default:
− - "Operation and maintenance manuals"
− - "As-built shop drawings"
− - "Factory production test reports"
− - "Field acceptance test reports per NETA ATS"
− - "Arc flash incident energy analysis and labels"
− - "Warranty documentation"
− - "Spare parts inventory with reorder information"
+ - "Record drawings"
+ - "Certified factory test report"
+ - "Field acceptance test reports"
+ - "Final trip unit and relay settings"
+ - "Operation and maintenance data"
+ - "Warranty certificate"
+ - "Spare parts and keys receipt"
```
…2 unchanged lines
## Manufacturer Qualifications {toc}
−### Switchboard shall be manufactured by a single company responsible for the assembly, bus, integral protective devices, and metering as a coordinated package.
+### The switchboard shall be produced by a manufacturer that has held a UL 891 listing for switchboards of the type furnished for not less than the period indicated in the datasheet.
−### The manufacturer shall have a minimum of five years documented experience producing UL 891 listed switchboards.
+```datasheet
+label: Minimum Manufacturer Listing History
+type: range
+unit: years
+options:
+ min: 0
+ max: 20
+ setpoints: [0, 3, 5, 10, 20]
+default: 5
+```
−### The manufacturer shall maintain an ISO 9001 certified quality management system.
+### The manufacturer shall maintain a factory-trained field service organization able to reach the site, and shall state in the qualification statement the location of the nearest service center and the period, measured from the date of manufacture, for which replacement devices and bus components for the switchboard platform will remain available.
−### The manufacturer shall maintain a service organization with factory-trained field representatives available within 24 hours of notification.
−
## Source Limitations {toc}
−### All switchboard sections, bus, circuit breakers, protective relays, instrument transformers, and metering equipment shall be produced or furnished by the switchboard manufacturer as an integrated assembly.
+### The structure, the bus, the device mounting, the main and feeder devices, and the compartments built into the structure shall be furnished by the switchboard manufacturer under one UL 891 listing.
−### Third-party retrofit or field-assembled enclosures are not acceptable.
+### Every switchboard on the project shall be furnished by one manufacturer, so that spare devices interchange and the Owner maintains one device family.
−### Devices and accessories shall be the manufacturer's standard catalog components for the listed assembly.
+### A device from another maker shall be installed in a switchboard only where the switchboard manufacturer has listed the device for the assembly under UL 891, and the assembly short-circuit current rating with that device installed shall be stated in the action submittals.
−## Listing {toc}
+### A meter, a relay, or a surge protective device from another maker remains covered by the assembly listing only where the switchboard manufacturer installed it in a compartment of its own construction and evaluated it as part of the assembly; a device added to the structure in the field without that evaluation removes the switchboard from the condition under which its rating was established. {note}
−### The complete switchboard, as assembled and shipped, shall bear the UL 891 listing label of a Nationally Recognized Testing Laboratory.
+## Field Testing Firm {toc}
−### Service entrance assemblies shall additionally be listed as Suitable for Use as Service Equipment (SUSE) per UL 869A.
+### Field acceptance testing shall be performed by the firm indicated in the datasheet.
−## Testing Personnel Qualifications {toc}
+```datasheet
+label: Field Acceptance Testing Firm
+type: radio
+options:
+ - "Independent testing firm accredited to ANSI/NETA ATS"
+ - "Manufacturer's field service organization"
+ - "Installing contractor's own technicians"
+```
−### Field acceptance testing shall be performed by a firm regularly engaged in testing electrical power equipment, employing technicians certified by NETA or equivalent.
+### The technicians who perform field acceptance testing shall hold a current certification for low-voltage equipment testing from NETA or from the manufacturer of the equipment tested, and shall have tested switchboards of the type furnished.
−### Testing personnel shall have a minimum of three years experience testing low voltage distribution equipment.
+### An independent firm has no stake in whether the switchboard passes and reports against a published acceptance standard; the manufacturer's organization knows the product best and is already on site where start-up services are furnished; the installing contractor's own technicians cost least and are available on the installer's schedule. Which of these the Owner wants depends on how the results will be used and on whether a report from the party who built or installed the equipment would satisfy the Owner's insurer and the Authority Having Jurisdiction. {note}
# Environmental and Service Conditions {toc}
−## Switchboard shall be suitable for continuous operation under the service conditions indicated in the datasheet.
+## Ambient Temperature {toc}
−## The design maximum ambient temperature at the installation shall be as indicated in the datasheet.
+### The switchboard shall carry its nameplate ratings continuously at the design ambient temperature of the space it is installed in.
+### The design ambient temperature for a switchboard installed indoors shall be as indicated in the datasheet.
+
```datasheet
−label: Ambient Temperature (Maximum)
+label: Indoor Design Ambient Temperature
type: range
unit: °C
options:
− min: 40
+ min: 25
max: 55
− setpoints: [40, 50, 55]
+ setpoints: [25, 30, 40, 50, 55]
default: 40
```
−## The elevated selections apply to specific installations: 50°C to elevated-ambient spaces and 55°C to rooftop or unconditioned spaces. {note}
+### UL 891 establishes the assembly ratings at a 40 °C ambient, and the circuit breakers inside are calibrated at 40 °C under UL 489, so a 40 °C design ambient is the condition at which every rating applies without correction; a higher value covers an electrical room whose ventilation cannot hold 40 °C at design load, at the cost of a larger bus or a larger device for the same load. {note}
−## The installation altitude shall be as indicated in the datasheet.
+### A switchboard installed outdoors or in a space that follows the outdoor temperature shall be rated for [[parameter: site-ambient-temperature-maximum]] where that temperature exceeds 40 °C, and the manufacturer shall state the derating applied in the action submittals.
−```datasheet
−label: Installation Altitude
−type: select
−options:
− - "Below 6,600 ft (2,000 m) - no derating"
− - "6,600 - 9,900 ft (2,000 - 3,000 m)"
− - "Above 9,900 ft (3,000 m) - consult manufacturer"
−default: "Below 6,600 ft (2,000 m) - no derating"
−```
+## Altitude {toc}
−## The corrosion severity classification of the installation environment shall be as indicated in the datasheet.
+### The switchboard and its devices shall be derated for [[parameter: altitude]] in accordance with the manufacturer's published correction factors where the altitude exceeds the 2000 m rating basis of the listing.
+### Air thins with altitude, which reduces both the convective cooling that sets the continuous current rating of the bus and the devices and the dielectric strength of the clearances inside the structure, so a switchboard rated at sea level carries less current and less insulation margin at elevation than its nameplate states. {note}
+
+### Ambient temperature derating and altitude derating shall be applied cumulatively where both conditions apply.
+
+## Condensation Control {toc}
+
+### Where the switchboard is installed outdoors or in a space that is not conditioned, a thermostatically controlled space heater shall be furnished in each vertical section.
+
+### Where space heaters are furnished, they shall be sized to hold the interior of each section above the dew point at [[parameter: site-ambient-temperature-minimum]], and shall be supplied from a circuit that stays energized while the switchboard main device is open.
+
+### A switchboard that stands in an unconditioned space cycles through the dew point with every cold night, and the condensation that forms on the bus, the device terminals, and the insulating supports is the mechanism behind most tracking failures on outdoor and unheated switchboards. {note}
+
+## Seismic Qualification {toc}
+
+### The seismic certification required for the switchboard shall be as indicated in the datasheet.
+
```datasheet
−label: Corrosion Severity
+label: Seismic Certification Requirement
type: select
+derived: "[[parameter: seismic-design-category]] and the component importance factor assigned to the switchboard under ASCE 7 Chapter 13"
options:
− - "C2 - Low (indoor, climate-controlled)"
− - "C3 - Medium (indoor, unconditioned)"
− - "C4 - High (coastal, chemical exposure)"
− - "C5 - Very High (industrial, marine)"
+ - "Not required"
+ - "Anchorage design only per ASCE 7 Chapter 13"
+ - "Special seismic certification by shake-table test per ICC-ES AC156 or by analysis accepted by the Authority Having Jurisdiction"
+default: derived
```
−## The corrosion classification is an assessment of the actual installation environment made by the Engineer; there is no classification that is correct for every project, so the field carries no default. {note}
+### Anchorage keeps the switchboard on its pad; special certification demonstrates that the devices in it still function after the design earthquake, which ASCE 7 requires of a component whose importance factor is above 1.0, such as a switchboard serving egress lighting, a fire pump, smoke control, or another load a Risk Category IV facility depends on. {note}
−## Where site conditions exceed these parameters, the Contractor shall notify the manufacturer and the equipment shall be derated accordingly.
+### Where seismic certification is required, it shall be performed in accordance with the seismic provisions of [[parameter: adopted-building-code]] and ASCE 7 Chapter 13, and the certificate shall cover the switchboard as furnished, including the structure, the bus, and every device installed, in the heaviest section arrangement furnished.
−## Equipment rated for standard conditions (40°C ambient, below 6,600 ft) shall be derated per the manufacturer's published derating curves and NEMA PB 2 when installed outside these parameters.
+### A certificate covering a single section, an empty structure, or a component tested apart from the assembly shall not be accepted as certification of the switchboard.
−## The Engineer shall document derating calculations on the contract drawings.
+### A field change to the devices installed or to the anchorage that departs from the certified configuration shall be re-evaluated by the manufacturer against the certification before the switchboard is energized.
−## For installations classified C4 or C5, bus bars shall be tin-plated or silver-plated copper, hardware shall be stainless steel, and the enclosure paint system shall provide enhanced corrosion protection.
+# Electrical Ratings {toc}
−## Seismic Requirements {toc}
+## Service Configuration {toc}
−### The seismic certification basis shall be as indicated in the datasheet.
+### Whether the switchboard is service equipment shall be as indicated in the datasheet.
```datasheet
−label: Seismic Certification
−type: select
−drawing_ref: "structural drawings"
+label: Service Configuration
+type: radio
+drawing_ref: "the one-line diagram"
options:
− - "Not required"
− - "IBC/ASCE 7 - Importance Factor 1.0"
− - "IBC/ASCE 7 - Importance Factor 1.5 (essential facility)"
− - "OSHPD pre-approval required (California healthcare)"
+ - "Service equipment"
+ - "Downstream distribution equipment"
default: deferred
```
−### The Seismic Design Category and Importance Factor are established by the project's structural design; the electrical scope adopts them rather than setting them. {note}
+### Where the switchboard is service equipment, it shall be listed and marked as suitable for use as service equipment under UL 891 and UL 869A and shall comply with NFPA 70 Article 230, including the service disconnecting means, the available fault current marking, the main bonding jumper, and the grounding electrode conductor termination furnished under [[sync/electrical-service-entrance]] and [[sync/grounding-and-bonding]].
−### Where required by the applicable building code, switchboard shall be seismically certified by shake-table testing per ICC ES AC156 or by analysis per ASCE 7.
+### Where the switchboard is service equipment, the number of service disconnects shall not exceed the number NFPA 70 230.71 permits for the service, each shall be marked as a service disconnect, and where more than one is furnished they shall be grouped in a section or sections separated from the remainder of the switchboard by a barrier as NFPA 70 230.71(B) requires.
−### Seismic certification shall be by an independent third-party testing laboratory and shall cover the complete assembly as installed, including all circuit breakers, bus, and ancillary components.
+### Where the switchboard is service equipment, the serving utility's metering requirements shall be confirmed in writing before the switchboard is released for manufacture, and the arrangement accepted shall be shown on the shop drawings.
−### Certification of individual components in isolation is not acceptable.
+## Main Arrangement {toc}
−### Anchorage details shall be coordinated with the structural engineer.
+### The main arrangement of the switchboard shall be as indicated in the datasheet.
−# Electrical Requirements {toc}
+```datasheet
+label: Main Arrangement
+type: select
+drawing_ref: "the one-line diagram"
+options:
+ - "Single main"
+ - "Double-ended, main-tie-main"
+ - "Multiple mains on a common bus"
+default: deferred
+```
−## System Ratings {toc}
+### A single main is the arrangement most switchboards are built with; a double-ended switchboard takes two sources onto two bus halves joined by a tie device, so that either source can carry the whole bus with the other out of service; multiple mains on a common bus is the service arrangement in which up to the number of disconnects NFPA 70 230.71 permits each protect a portion of the bus without a single main. {note}
−### Whether the switchboard serves as main service entrance equipment shall be as indicated in the datasheet.
+### Where a main-tie-main arrangement is furnished, the two mains and the tie shall be interlocked so that not more than two of the three devices can be closed at one time unless the one-line diagram indicates a closed-transition scheme, and the interlock method shall be as indicated in the datasheet.
```datasheet
−label: Service Entrance Equipment
+label: Main-Tie-Main Interlock Method
type: radio
−drawing_ref: "one-line diagram"
options:
− - "Main service entrance equipment (UL 869A SUSE)"
− - "Downstream distribution equipment"
−default: deferred
+ - "Key interlock"
+ - "Electrical interlock through the device auxiliary contacts"
+ - "Key and electrical interlock"
```
+### A key interlock enforces the two-of-three rule mechanically and works with the control power lost, but it depends on the operator carrying the key between devices; an electrical interlock acts through the device trip and close circuits and lends itself to an automatic transfer scheme, but it is only as good as the control power that feeds it; furnishing both covers each one's failure mode at the cost of both. {note}
+
+### Where the one-line diagram indicates an automatic transfer scheme at a main-tie-main switchboard, the transfer controller, its sensing, and its time delays shall be furnished by the switchboard manufacturer under the assembly listing, and the devices it operates shall be electrically operated.
+
+## System Voltage and Frequency {toc}
+
### The system voltage and configuration shall be as indicated in the datasheet.
```datasheet
label: System Voltage
type: select
−drawing_ref: "one-line diagram"
+drawing_ref: "the one-line diagram"
options:
− - "120/208V 3Φ 4-wire"
− - "277/480V 3Φ 4-wire"
− - "480V 3Φ 3-wire"
− - "240V 3Φ 3-wire"
− - "240/120V 1Φ 3-wire"
+ - "120/240 V 1Φ 3-wire"
+ - "208Y/120 V 3Φ 4-wire"
+ - "240 V 3Φ 3-wire delta"
+ - "240/120 V 3Φ 4-wire high-leg delta"
+ - "480Y/277 V 3Φ 4-wire"
+ - "480 V 3Φ 3-wire delta"
+ - "600Y/347 V 3Φ 4-wire"
+ - "600 V 3Φ 3-wire delta"
default: deferred
```
+### The number of phases and the number of wires follow from the system voltage selected, and the number of poles on the devices and the presence of a neutral bus follow from them in turn. {note}
+
+### The switchboard voltage rating shall equal or exceed the system voltage, and where the switchboard is fed from a transformer secondary the Contractor shall confirm the rating against the secondary configuration of the transformer before the switchboard is released for manufacture.
+
+### Where the system is a high-leg delta, the high leg shall be connected to the B phase of the bus and shall be identified in accordance with NFPA 70 110.15 and 408.3(F).
+
+### Where the system is a 3-wire delta or another system with no grounded conductor at the switchboard, the switchboard shall be furnished without a neutral bus and the devices shall be rated for the line-to-line voltage.
+
### The system frequency shall be as indicated in the datasheet.
```datasheet
label: System Frequency
type: radio
−unit: Hz
options:
- "60 Hz"
…2 unchanged lines
```
−### 60 Hz is the North American norm and is the datasheet default; 50 Hz equipment is a distinct product selection, available for systems that operate at that frequency. {note}
+## Main Bus Continuous Current {toc}
−### Where the switchboard serves as main service entrance equipment, it shall be listed as Suitable for Use as Service Equipment per UL 869A and shall comply with NFPA 70 Article 230 including provisions for service disconnect, utility metering, neutral-to-ground bonding, and available fault current labeling per NFPA 70 Article 110.24.
+### The main bus continuous current rating shall be as indicated in the datasheet.
−### Coordinate metering current transformer compartment and termination requirements with the serving utility prior to submittal.
−
−## Bus Rating {toc}
−
−### Main bus continuous current rating shall be as indicated in the datasheet.
−
```datasheet
label: Main Bus Continuous Current
type: range
unit: A
−drawing_ref: "one-line diagram"
+drawing_ref: "the one-line diagram"
options:
min: 400
− max: 5000
− setpoints: [400, 600, 800, 1200, 1600, 2000, 2500, 3000, 4000, 5000]
+ max: 6000
+ setpoints: [400, 600, 800, 1000, 1200, 1600, 2000, 2500, 3000, 3200, 4000, 5000, 6000]
default: deferred
```
−### The switchboard short-circuit current rating shall be as indicated in the datasheet.
+### The main bus rating shall be not less than the rating of the main device where one is furnished, not less than the rating of the feeder overcurrent device ahead of the switchboard where it has main lugs only, and not less than the sum of the ratings of the service disconnects where multiple mains are furnished without a single main.
−```datasheet
−label: Switchboard Short-Circuit Current Rating (SCCR)
−type: range
−unit: kAIC
−drawing_ref: "one-line diagram"
−options:
− min: 25
− max: 200
− setpoints: [25, 35, 42, 65, 85, 100, 200]
−default: deferred
−```
+### The bus rating is fixed by the calculated load of NFPA 70 Article 220, the transformer or service ahead of the switchboard, and the spare capacity the project wants to leave, and it is stated on the one-line diagram with the main device that protects it; a bus cannot be uprated after manufacture without replacing the sections that carry it, which is why the rating is chosen against the ultimate source rating rather than the first-day load. {note}
−### The short-circuit withstand duration shall be as indicated in the datasheet.
+### The through-bus rating basis for the distribution sections shall be as indicated in the datasheet.
```datasheet
−label: Short-Circuit Withstand Duration
−type: select
+label: Through-Bus Rating Basis
+type: radio
options:
− - "3-cycle (0.05 seconds) - standard MCCB"
− - "30-cycle (0.5 seconds) - ICCB with short-time rating"
−default: "3-cycle (0.05 seconds) - standard MCCB"
+ - "Full main bus rating through every section"
+ - "Tapered, each section rated for the load it and the sections beyond it carry"
```
−### Bus shall be braced for the available short-circuit current at the point of installation as determined by a short-circuit analysis.
+### A full-rated through-bus carries the main bus rating to the far end of the lineup, so that a feeder of any rating can be added in any section and a section can be added at the end without re-rating the bus; a tapered through-bus is sized in each section for the devices actually downstream of it, which saves bus material on a long lineup and fixes the lineup to the device arrangement it was built for. {note}
−### The complete switchboard, including main and feeder devices, shall carry a UL 891 short-circuit current rating (SCCR) equal to or greater than the available fault current.
+### Where a tapered through-bus is selected, the rating of the bus in each section shall be shown on the shop drawings, and no feeder device shall be installed in a section whose through-bus rating is less than the sum of the feeder ratings it carries.
−### Switchboard short-circuit current rating shall equal or exceed the available fault current at the line-side terminals.
+## Short-Circuit Current Rating {toc}
−### Verify available fault current with the utility provider and perform a short-circuit study per [[sync/short-circuit-study]] prior to equipment procurement.
+### The available fault current at the line terminals of each switchboard shall be as indicated on [[drawing: the one-line diagram]].
−### Series-rated combinations between main and feeder devices are permitted only when the combination is tested and listed by the manufacturer.
+### The assembly short-circuit current rating marked on the nameplate of each switchboard shall equal or exceed the available fault current at its line terminals as established under [[sync/short-circuit-study]], and shall be as indicated in the datasheet.
−### Series ratings shall not be used where downstream motor contribution invalidates the rating per NFPA 70 Article 240.86.
+```datasheet
+label: Assembly Short-Circuit Current Rating
+type: range
+unit: kA
+drawing_ref: "the one-line diagram"
+options:
+ min: 22
+ max: 200
+ setpoints: [22, 25, 35, 42, 50, 65, 85, 100, 150, 200]
+default: deferred
+```
−### A 30-cycle short-time withstand rating is required where selective coordination with downstream breakers must be maintained without instantaneous trip on the upstream main.
+### The marked assembly rating is the lowest of the bus bracing, the interrupting rating of the main device, and the interrupting rating of every feeder device, or the rating of the series-rated combination that covers them, so a single device of a lower rating installed in the field lowers the rating of the whole switchboard. {note}
−### A 30-cycle short-time withstand rating typically requires insulated-case circuit breakers (ICCBs) for the main device. {note}
+### The bus short-circuit bracing shall be as indicated in the datasheet.
−## Neutral and Ground Bus {toc}
+```datasheet
+label: Bus Short-Circuit Bracing
+type: range
+unit: kA
+derived: "the assembly short-circuit current rating; the bus is braced to not less than the rating marked on the switchboard"
+options:
+ min: 22
+ max: 200
+ setpoints: [22, 25, 35, 42, 50, 65, 85, 100, 150, 200]
+default: derived
+```
−### The neutral bus rating shall be as indicated in the datasheet.
+### The short-time withstand rating of the assembly shall be as indicated in the datasheet.
```datasheet
−label: Neutral Bus Rating
−type: select
+label: Short-Time Withstand Rating
+type: radio
options:
− - "Not applicable (3-wire system, no neutral)"
− - "100% of main bus rating"
− - "50% of main bus rating (reduced)"
− - "200% of main bus rating (oversized for harmonic loads)"
−default: "100% of main bus rating"
+ - "3-cycle short-circuit rating only"
+ - "30-cycle short-time withstand rating"
+default: "3-cycle short-circuit rating only"
```
−### A 3-wire system with no neutral records "Not applicable" rather than leaving the field ambiguous. {note}
+### A UL 891 switchboard is tested to carry its short-circuit current for 3 cycles, which is the time a molded-case device takes to clear, and that is the construction most switchboards are built with; a 30-cycle short-time rating braces the bus and the structure to carry the fault for a half second, which is what a main device needs if its instantaneous element is to be set above the arcing current or defeated so that a downstream device clears first. The 30-cycle rating is bought with heavier bus supports and a main whose frame carries a short-time rating, and it is the construction a selectively coordinated system often requires at the main. {note}
−### Oversized neutral bus shall be specified where nonlinear loads exceed 30% of the total connected load to accommodate triplen harmonic currents.
+### Where a 30-cycle short-time withstand rating is selected, the main device shall carry a short-time rating not less than the assembly rating for 30 cycles, and the bus bracing shall be established for that duration.
−### The Engineer shall evaluate harmonic loading per IEEE 519 when selecting neutral bus sizing.
+## Interrupting Rating Basis {toc}
−### Whether a ground bus is furnished with the assembly shall be as indicated in the datasheet.
+### The basis on which the interrupting ratings of the devices in the switchboard are established shall be as indicated in the datasheet.
```datasheet
−label: Ground Bus
+label: Interrupting Rating Basis
type: radio
options:
− - "Included — full length of the assembly"
− - "Not required"
−default: "Included — full length of the assembly"
+ - "Fully rated"
+ - "Series rated"
+default: "Fully rated"
```
−### A full-length ground bus is the normal construction and is the datasheet default; "Not required" exists for the rare addition to an existing line-up whose ground bus is carried through from the adjoining sections. {note}
+### In a fully rated switchboard every device carries an interrupting rating that stands on its own at the available fault current; in a series-rated switchboard the feeder devices carry a lower individual rating and reach the marked rating only in combination with the specific upstream device they were tested with, which NFPA 70 240.86 permits where the combination is listed. Series rating lowers the cost of the feeder devices where the available fault current is high, and it makes the rating depend on an upstream device that must stay in place for the life of the installation. The switchboard stands at the head of the system, where the fault current is highest and where the device it would depend on is a utility fuse or sits in another assembly, which is why a fully rated switchboard is the norm here while the series combinations a project uses are more often applied in the panelboards it feeds. {note}
−### Where a ground bus is furnished, it shall be bare copper, minimum 1/4 in. x 2 in. cross-section, extending the full length of the switchboard assembly.
+### The interrupting rating of the feeder devices shall be as indicated in the datasheet.
−### Ground bus shall be accessible without removing any covers or barriers required for safe operation.
+```datasheet
+label: Feeder Device Interrupting Rating
+type: range
+unit: kA
+derived: "the assembly short-circuit current rating and the interrupting rating basis; under a fully rated basis every device equals or exceeds the assembly rating, and under a series rated basis the listed combination fixes the feeder device rating"
+options:
+ min: 22
+ max: 200
+ setpoints: [22, 25, 35, 42, 50, 65, 85, 100, 150, 200]
+default: derived
+```
−### Bonding between the ground bus and the equipment enclosure shall be per [[sync/grounding-and-bonding]].
+### Where series rating is the basis, the combination shall be one the manufacturer has tested and listed under UL 891 and UL 489 in accordance with NFPA 70 240.86(B), and the upstream device on which each rating depends shall be identified in the action submittals.
−# Physical Construction {toc}
+### Where series rating is the basis, the switchboard shall be field-marked in accordance with NFPA 70 110.22(C) to identify the series combination and the replacement devices it depends on.
−## Enclosure {toc}
+### Where series rating is the basis, the Contractor shall confirm that the sum of the motor full-load currents connected between the upstream device and the feeder device does not exceed the limit NFPA 70 240.86(C) sets for the feeder device rating, and shall report a combination that exceeds it to the Engineer of Record before the switchboard is released for manufacture.
−### The enclosure NEMA rating shall be as indicated in the datasheet.
+### Where the switchboard serves a system that NFPA 70 Article 700, 701, or 708 requires to be selectively coordinated, a series-rated combination shall not be relied on within the coordinated path, because the upstream device of a series combination opens with the feeder device on a high-magnitude fault.
+### Where a device in a series-rated switchboard is replaced, the replacement shall be of the same manufacturer, type, and rating named in the listed combination.
+
+## Neutral Bus {toc}
+
+### The neutral bus shall be as indicated in the datasheet.
+
```datasheet
−label: Enclosure Rating
+label: Neutral Bus
type: select
+derived: "the system voltage configuration and the share of nonlinear load served from the switchboard"
options:
− - "NEMA 1 - Indoor General Purpose"
− - "NEMA 1A - Indoor Gasketed (dust-resistant)"
− - "NEMA 3R - Outdoor Rainproof"
− - "NEMA 12 - Industrial (dust-tight)"
−default: "NEMA 1 - Indoor General Purpose"
+ - "No neutral bus"
+ - "Neutral bus rated 50% of the phase bus"
+ - "Neutral bus rated 100% of the phase bus"
+ - "Neutral bus rated 200% of the phase bus"
+default: derived
```
−### The accessibility configuration shall be as indicated in the datasheet.
+### A three-wire system has no neutral to carry; a four-wire system whose load is largely three-phase or balanced line-to-neutral carries a neutral that NFPA 70 220.61 lets be reduced below the phase bus; a four-wire system with ordinary single-phase load carries one rated with the phase bus; and a four-wire system whose load is predominantly single-phase nonlinear equipment, such as switch-mode power supplies, LED drivers, and single-phase drives, carries the triplen harmonic currents that add in the neutral rather than cancel, which is the condition under which the neutral is rated above the phase bus. {note}
+### Where a neutral bus is furnished, it shall be insulated from the structure, shall extend the full length of the switchboard, and where the switchboard is service equipment the main bonding jumper shall be furnished by the manufacturer and installed in accordance with [[sync/grounding-and-bonding]].
+
+### Where a neutral bus is furnished, a neutral terminal shall be furnished for every feeder device position, including spare and space positions, sized for the neutral conductor of the feeder it serves.
+
+## Ground Bus {toc}
+
+### The ground bus shall be as indicated in the datasheet.
+
```datasheet
−label: Accessibility
+label: Ground Bus
type: radio
options:
− - "Front accessible (rear against wall)"
− - "Front and rear accessible"
−default: "Front accessible (rear against wall)"
+ - "Full-length ground bus"
+ - "No ground bus"
+default: "Full-length ground bus"
```
−### The number of vertical sections shall be as indicated in the datasheet.
+### A switchboard added to an existing lineup whose ground bus continues through the joined sections is the case in which a ground bus of its own is omitted; every free-standing switchboard carries one. {note}
−```datasheet
−label: Number of Vertical Sections
−type: range
−unit: sections
−drawing_ref: "one-line diagram"
−options:
− min: 1
− max: 12
− step: 1
−default: deferred
−```
+### Where a ground bus is furnished, it shall be copper of not less than 1/4 in. by 2 in. cross-section, shall be bonded to each section of the structure, shall extend the full length of the switchboard, and shall carry a terminal for the equipment grounding conductor of every feeder device position.
−### The conduit entry direction shall be as indicated in the datasheet.
+### The ground bus shall be accessible from the front of each section without removing a bus barrier or a device cover.
+### Grounding and bonding of the switchboard shall comply with [[sync/grounding-and-bonding]].
+
+# Main Device {toc}
+
+## Main Device Type {toc}
+
+### The main device of the switchboard shall be as indicated in the datasheet.
+
```datasheet
−label: Conduit Entry
+label: Main Device Type
type: select
−drawing_ref: "electrical plans"
+drawing_ref: "the one-line diagram"
options:
− - "Top entry"
− - "Bottom entry"
− - "Top and bottom entry"
+ - "Main lugs only"
+ - "Main circuit breaker"
+ - "Main fusible switch"
+ - "Main bolted-pressure switch with fuses"
default: deferred
```
−### Enclosure shall be free-standing, dead-front, fabricated from cold-rolled steel with a minimum thickness of 12 gauge (2.66 mm) for structural members and 14 gauge (1.90 mm) for covers and doors.
+### The main device frame size and trip rating, or the switch rating and the fuse class and rating, shall be as indicated on [[drawing: the one-line diagram]].
−### Sections shall be of uniform height and depth and shall align flush across the front.
+### A main circuit breaker gives the switchboard a disconnecting means and an overcurrent device at the assembly, and its trip unit is the place the coordination study sets the main's characteristic; main lugs only leaves both functions to the device upstream and saves the cost and the section of the main, which is the construction a switchboard fed from a transformer secondary device or from another assembly's feeder is built with; a main fusible switch is the construction used where the fault current calls for a current-limiting fuse or where the Owner's device family is fused; a bolted-pressure switch is the fused main built for the large service, with contacts clamped under bolt pressure after closing so that the switch carries the full bus current without heating at the blades. {note}
−### All joints shall be continuously welded or bolted with gaskets as required for the specified NEMA rating.
+### Where the switchboard has main lugs only, it shall be protected by an overcurrent device on the supply side whose rating does not exceed the bus rating, in accordance with NFPA 70 408.36, and that device shall be accessible as the disconnecting means for the switchboard.
−### For outdoor installations (NEMA 3R), enclosure shall include rain hoods over ventilation openings, drip shields above doors, and condensation heaters in each section.
+### Where the switchboard is service equipment and has a single main, the main device shall be the service disconnecting means and shall be rated in accordance with NFPA 70 Article 230.
−### Heater sizing shall be a minimum of 200W per vertical section.
+### Where a main fusible switch or a bolted-pressure switch is furnished, it shall be listed to UL 98 or UL 977 for the rating furnished, shall carry an interrupting rating with the fuse class installed not less than the assembly rating, and shall be furnished with rejection-type fuse clips for the fuse class indicated on the one-line diagram.
−### Heaters shall be thermostat controlled and wired to remain energized whenever the switchboard is de-energized.
+### Where a bolted-pressure switch is furnished, it shall be electrically operated with a stored-energy mechanism and shall be furnished with blown-fuse indication and an open-fuse trip that opens the switch when any one fuse opens.
−### Front-accessible switchboards permit installation against a wall, which is the most common configuration. {note}
+### The main device operating handle shall accept a padlock in the open position.
−### Rear-accessible configurations require minimum 36 in. working clearance at the rear per NFPA 70 Article 110.26 and shall have individual hinged rear doors or removable rear covers for access to bus connections and line/load lugs.
+## Main Circuit Breaker Construction {toc}
−### Switchboard location and arrangement shall be [[drawing: as indicated on the equipment room layout drawings]].
+### Where a main circuit breaker is furnished, its construction shall be as indicated in the datasheet.
−### Coordinate section count and overall length with shipping splits to ensure equipment can be transported to and through the installation pathway.
+```datasheet
+label: Main Circuit Breaker Construction
+type: select
+options:
+ - "Molded-case circuit breaker, fixed-mounted"
+ - "Insulated-case circuit breaker, fixed-mounted"
+ - "Insulated-case circuit breaker, drawout-mounted"
+ - "Low-voltage power circuit breaker, drawout-mounted"
+```
−### Conduit entry zones shall be coordinated with the section construction to maintain required bending space per NFPA 70 Article 312.6 and shall avoid interference with bus, devices, and barriers.
+### A molded-case breaker is the smallest and least expensive main, is built with a thermal-magnetic or an electronic trip unit, and clears every fault instantaneously in the larger frames, which limits how a downstream device can be coordinated with it; an insulated-case breaker is a molded-case breaker built on a stored-energy, two-step mechanism with a short-time rating, which lets its instantaneous element be set high or defeated so that a feeder device clears first, and it is the construction the 30-cycle short-time withstand rating is built on; mounting the insulated-case breaker drawout lets it be racked out for inspection or exchange with the bus energized, at the cost of the drawout cradle and the section depth it needs; a low-voltage power circuit breaker listed to IEEE C37.13 can be furnished in a UL 891 switchboard where a project wants its 30-cycle rating and its maintainable contacts, and the assembly remains a switchboard listed to UL 891 rather than switchgear. {note}
−## Bus Bars {toc}
+### Where a drawout-mounted main is furnished, the cradle shall carry connected, test, and disconnected positions, shall have a position indicator visible with the door closed, and shall interlock so that the breaker cannot be racked between the connected and disconnected positions while closed.
−### The bus bar material and plating shall be as indicated in the datasheet.
+### Where a drawout-mounted main is furnished, automatic shutters shall cover the primary disconnects when the breaker is withdrawn.
+### Where a main circuit breaker is furnished, it shall be electrically operated where the one-line diagram indicates a transfer scheme, a remote operator, or a ground-fault or arc-flash scheme that closes or opens the main from a remote contact.
+
+## Main Circuit Breaker Trip Unit {toc}
+
+### Where a main circuit breaker is furnished, its trip unit shall be as indicated in the datasheet.
+
```datasheet
−label: Bus Bar Material
−type: radio
+label: Main Circuit Breaker Trip Unit
+type: select
+drawing_ref: "the one-line diagram"
options:
− - "Copper (unplated bar, plated joint contact surfaces)"
− - "Copper (tin-plated)"
− - "Copper (silver-plated)"
− - "Aluminum (tin-plated)"
+ - "Thermal-magnetic"
+ - "Electronic with long-time and instantaneous functions"
+ - "Electronic with long-time, short-time, and instantaneous functions"
+ - "Electronic with long-time, short-time, instantaneous, and ground-fault functions"
+default: deferred
```
−### The bus insulation treatment shall be as indicated in the datasheet.
+### A thermal-magnetic trip unit has a fixed time-current characteristic, an instantaneous setting that is adjustable on the larger frames only, and no communications, and it is the construction the smaller frames are built with; an electronic trip unit has adjustable long-time, short-time, and instantaneous settings, which is what selective coordination with the feeder devices is set with, and it is the construction the larger frames are built with; the ground-fault function on an electronic trip unit is one of the two ways ground-fault protection of equipment is furnished where code requires it. {note}
+### Where a main circuit breaker with an electronic trip unit is furnished, its settings shall be as established under [[sync/protective-coordination-study]], and the settings as commissioned shall be recorded in the closeout submittals.
+
+### Where an electronic trip unit is furnished, it shall display the settings applied and the cause of the last trip at the device, and shall carry a test port for secondary injection testing.
+
+## Ground-Fault Protection of Equipment {toc}
+
+### Ground-fault protection of equipment on the main device shall be as indicated in the datasheet.
+
```datasheet
−label: Bus Insulation
−type: radio
+label: Ground-Fault Protection of Equipment on the Main Device
+type: select
+derived: "NFPA 70 230.95 and 215.10 applied to the system voltage, the main device rating, and whether the switchboard is service equipment"
options:
− - "Bare bus with isolation barriers"
− - "Fully insulated (flame-retardant sleeving or coating)"
−default: "Bare bus with isolation barriers"
+ - "Not provided"
+ - "Integral to the main circuit breaker electronic trip unit"
+ - "Separate ground-fault relay and sensor listed to UL 1053"
+default: derived
```
−### The bus current density basis shall be as indicated in the datasheet.
+### Whether the main device must carry ground-fault protection of equipment is fixed by code from the system grounding, the voltage to ground, and the device rating, so the field records the consequence of those inputs rather than a preference; a project can add ground-fault protection where code does not require it, and where it is required the means of providing it is the project selection, with the separate relay being the means used on a fused main, which has no trip unit to carry the function. {note}
+### Where ground-fault protection of equipment is furnished, it shall open all ungrounded conductors of the switchboard at a ground-fault pickup not exceeding 1200 A and within one second for a ground-fault current of 3000 A or more, in accordance with NFPA 70 230.95(A).
+
+### Where ground-fault protection of equipment is furnished on a switchboard that is not service equipment, its pickup and delay shall be set to coordinate with the ground-fault protection upstream as established under [[sync/protective-coordination-study]].
+
+### Where ground-fault protection of equipment is furnished on the main and the feeders carry ground-fault functions of their own, the main's ground-fault delay shall be set so that a feeder clears its own ground fault before the main opens, and where the switchboard serves a health care facility the two levels shall be coordinated as NFPA 70 517.17 requires.
+
+### Where ground-fault protection of equipment is furnished, the Contractor shall have it performance-tested by primary current injection after installation in accordance with NFPA 70 230.95(C), and the written record shall be delivered with the closeout submittals.
+
+### Ground-fault protection of equipment protects the bus and the conductors from the arcing damage of a low-magnitude ground fault that the main device would not clear promptly; it does not protect a person, and it is not a substitute for the ground-fault circuit-interrupter protection NFPA 70 210.8 requires on branch circuits. {note}
+
+## Arc Energy Reduction {toc}
+
+### Where a circuit breaker in the switchboard is rated or can be adjusted to 1200 A or more, arc energy reduction shall be provided in accordance with NFPA 70 240.87 by the method indicated in the datasheet.
+
```datasheet
−label: Bus Density
+label: Arc Energy Reduction Method
type: select
−unit: A/in²
+derived: "NFPA 70 240.87 applied to the rating of the main device and of each feeder device shown on the one-line diagram"
options:
− - "1000 A/in² (standard, 65°C rise)"
− - "750 A/in² (conservative, 50°C rise)"
−default: "1000 A/in² (standard, 65°C rise)"
+ - "Not applicable, no device rated 1200 A or more"
+ - "Energy-reducing maintenance switching with local status indicator"
+ - "Zone-selective interlocking"
+ - "Differential relaying"
+ - "Energy-reducing active arc-flash mitigation system"
+ - "Instantaneous trip setting below the available arcing current"
+default: derived
```
−### Provisions for future bus extension shall be as indicated in the datasheet.
+### Whether arc energy reduction is required is fixed by the device rating, so the field carries the consequence of the one-line diagram; only the method is a project selection where the threshold is met. {note}
+### An energy-reducing maintenance switch lowers the instantaneous pickup for the duration of the work and depends on a worker turning it on; zone-selective interlocking and differential relaying act without a worker's intervention but need the downstream devices or the current transformers to be part of the scheme; an active mitigation system detects the arc by light and current and clears it faster than any trip unit, at the highest cost; an instantaneous setting below the arcing current works only where the arcing current at the switchboard is well above the load current, and it is the method a fused main cannot use. {note}
+
+### Where energy-reducing maintenance switching is selected, the switch shall be lockable in the maintenance position and its status shall be indicated at the switch and, where a network is furnished, over the network.
+
+### Where a fused main rated 1200 A or more is furnished, arc energy reduction shall be provided in accordance with NFPA 70 240.67 by a method the fuse and switch combination supports, and the method shall be identified in the action submittals.
+
+### Where arc energy reduction is furnished, the Contractor shall perform the performance test NFPA 70 240.87(C) requires and shall deliver the documentation NFPA 70 240.87(A) requires with the closeout submittals.
+
+# Feeder Devices {toc}
+
+## Feeder Device Type {toc}
+
+### The feeder devices of the switchboard shall be as indicated in the datasheet.
+
```datasheet
−label: Bus Extension Provisions
−type: radio
+label: Feeder Device Type
+type: select
options:
− - "No future extension"
− - "Provision for future extension at one end"
−default: "No future extension"
+ - "Molded-case circuit breakers, group-mounted"
+ - "Molded-case and insulated-case circuit breakers, individually mounted"
+ - "Fusible switches, group-mounted"
+ - "Fusible switches, individually mounted"
+default: "Molded-case circuit breakers, group-mounted"
```
−### Aluminum bus shall be specified only where explicitly accepted by the Owner and shall be tin-plated at all joint contact surfaces.
+### Where the one-line diagram indicates a device type for a particular feeder that differs from the datasheet selection, the one-line diagram shall govern for that feeder.
−### Copper is preferred for service entrance equipment and for installations in corrosive environments. {note}
+### Group-mounted molded-case breakers bolt side by side onto a common panel-mounted bus in a distribution section, which gives the highest device density per section and the lowest cost, and it is the construction most switchboards are built with; individual mounting gives each device its own compartment and its own bus connection, which is how the larger frames are mounted and how a project separates feeders so that work on one does not expose the line side of its neighbors; fusible switches are the construction used where the Owner's device family is fused or where the current-limiting fuse is what holds the downstream rating. {note}
−### Bus bar joints shall be bolted with Belleville washers to maintain contact pressure under thermal cycling.
+### The frame size, the pole count, the trip rating, and the fuse class and rating of every feeder device shall be as indicated on [[drawing: the one-line diagram]].
−### All joint contact surfaces shall be plated.
+### Every feeder device shall be rated for the system voltage, and a feeder circuit breaker shall be listed to UL 489 and built to NEMA AB 1.
−### Bus connections shall be accessible for re-torquing during maintenance.
+### Multi-pole feeder breakers shall be common-trip, so that every pole opens when any pole trips.
−### Fully insulated bus shall be specified for outdoor (NEMA 3R) installations, for service entrance equipment over 1200A, and where required by Owner standards.
+### Every feeder device shall have a trip-free mechanism, a handle that indicates the on, off, and tripped positions, and a handle that accepts a padlock in the open position.
−### Bus insulation shall be flame-retardant and shall be continuous through barriers and bus transitions between sections.
+### Where fusible feeder switches are furnished, each shall be listed to UL 98, shall be furnished with rejection-type fuse clips for the fuse class indicated on the one-line diagram, and shall be interlocked so that its cover cannot be opened with the switch closed.
−## Barriers and Compartmentalization {toc}
+## Feeder Trip Units {toc}
−### The degree of internal compartmentalization shall be as indicated in the datasheet.
+### The trip unit of the feeder circuit breakers shall be as indicated in the datasheet.
```datasheet
−label: Compartment Form (per NEMA PB 2 form designations)
+label: Feeder Circuit Breaker Trip Unit
type: select
+drawing_ref: "the one-line diagram"
options:
− - "Form 1 - No internal segregation"
− - "Form 2 - Bus segregated from devices"
− - "Form 3 - Bus segregated from devices, devices segregated from each other"
− - "Form 4 - Bus, devices, and terminals all segregated"
−default: "Form 2 - Bus segregated from devices"
+ - "Thermal-magnetic"
+ - "Electronic with long-time and instantaneous functions"
+ - "Electronic with long-time, short-time, and instantaneous functions"
+ - "Electronic with long-time, short-time, instantaneous, and ground-fault functions"
+default: deferred
```
−### Switchboard shall provide insulating or metal barriers between the main bus compartment and the device/cable compartments.
+### Where the one-line diagram indicates a trip unit type for a particular feeder that differs from the datasheet selection, the one-line diagram shall govern for that feeder.
−### Barriers shall reduce the likelihood of an arc fault propagating from one compartment to adjacent compartments.
+### A thermal-magnetic feeder breaker is the construction the frames below about 400 A are built with and costs least; an electronic trip unit on a feeder is what lets that feeder be coordinated with the main above it and the panelboard main below it, and its ground-fault function is one of the two ways NFPA 70 215.10 is satisfied on a feeder that requires ground-fault protection of equipment. {note}
−### Through-bus shall be barriered from feeder breaker line-side connections by isolating barriers.
+### Where a feeder circuit breaker with an electronic trip unit is furnished, its settings shall be as established under [[sync/protective-coordination-study]], and the settings as commissioned shall be recorded in the closeout submittals.
−### Higher form designations reduce the risk of cascading faults during maintenance but increase cost and physical size. {note}
+### Where NFPA 70 215.10 requires ground-fault protection of equipment on a feeder, it shall be furnished at that feeder device unless the one-line diagram indicates that the ground-fault protection on the main satisfies the requirement for that feeder.
−### Form 3 or 4 should be specified for mission-critical facilities, healthcare, and data centers.
+## Device Accessories {toc}
−## Arc Flash Mitigation {toc}
+### Shunt trips, undervoltage releases, auxiliary contacts, bell alarm contacts, motor operators, key interlocks, and mechanical interlocks shall be furnished on the devices designated on [[drawing: the one-line diagram]].
−### See [[sync/arc-flash-study]] for arc flash study requirements and labeling. {note}
+### A shunt trip lets a device be opened from a remote contact, as at a kitchen hood suppression system, an emergency power off station, or a fire alarm interface; an undervoltage release opens the device when its control voltage is lost, which is the behavior wanted on a device that must not stay closed through a loss of control power and the behavior to avoid on one that must; an auxiliary contact reports the device position to a control or monitoring system; a bell alarm contact reports a trip as distinct from a manual opening; a motor operator lets the device be closed and opened from a remote point or by a transfer controller. {note}
−### Where arc energy reduction is required, the method shall be as indicated in the datasheet.
+### Where a shunt trip or an undervoltage release is furnished, its control voltage and the source of its signal shall be as indicated on [[drawing: the one-line diagram]], and the circuit shall be tested through its initiating device before the switchboard is accepted.
+### Every accessory shall be the device manufacturer's accessory listed for the frame it is installed on, and shall be installed by the switchboard manufacturer under the assembly listing.
+
+## Spare Devices and Spaces {toc}
+
+### The share of feeder device positions in each switchboard left for future feeders shall be not less than the share indicated in the datasheet, in addition to the spare and space positions the one-line diagram designates.
+
```datasheet
−label: Arc Energy Reduction Method (1200A+ Devices)
−type: select
+label: Minimum Spare Feeder Positions
+type: range
+unit: '%'
options:
− - "Zone-selective interlocking (ZSI)"
− - "Energy reducing maintenance switch (ERMS)"
− - "Differential relaying"
− - "Approved equivalent method"
−default: "Energy reducing maintenance switch (ERMS)"
+ min: 0
+ max: 30
+ setpoints: [0, 10, 15, 20, 25, 30]
```
−### Where arc-resistant construction is specified for the project, the accessibility type shall be as indicated in the datasheet.
+### The form in which spare positions are furnished shall be as indicated in the datasheet.
```datasheet
−label: Arc-Resistant Construction
−type: select
+label: Spare Position Provision
+type: radio
options:
− - "Not required"
− - "Type 1 - front"
− - "Type 2 - front, rear, and sides"
+ - "Bussed spaces with mounting hardware and covers"
+ - "Spare devices installed"
```
−### Arc-resistant construction is an added-cost option rather than a baseline requirement; projects that do not specify it record "Not required", and the field is left blank until the decision is made. {note}
+### A bussed space is a position with its bus connection, its mounting hardware, and a blank cover in place, ready to receive a device of any listed frame that fits it without drilling live bus; a spare device installed is a device bought now, marked spare, and left open, which lets a feeder be added without a purchase but commits the frame and the trip rating in advance. {note}
−### Switchboard shall include arc flash hazard reduction features appropriate to the connected system.
+### Where spare devices are installed, the frame size and trip rating of the spares shall be as indicated on [[drawing: the one-line diagram]], and each spare shall be left in the open position and identified as a spare.
−### Arc flash hazard analysis shall be performed per IEEE 1584.
+### Every space position shall be bussed and provided with the mounting hardware needed to receive a device without modifying the bus or the structure, and shall be covered by a blank cover when the switchboard is delivered.
−### NFPA 70 Article 240.87 requires that circuit breakers rated 1200A or more provide an arc energy reduction method.
+# Bus {toc}
−### ERMS is the most common solution for switchboard applications because it does not require coordination across multiple breakers and can be activated by a maintenance technician via a front-mounted switch with status indication. {note}
+## Phase Bus Material {toc}
−### Where arc-resistant construction is specified, switchboard shall be tested per IEEE C37.20.7 at the specified short-circuit current rating and duration.
+### The phase bus material shall be as indicated in the datasheet.
−### Arc-resistant construction does not eliminate the need for arc flash hazard analysis or arc flash labeling.
+```datasheet
+label: Phase Bus Material
+type: radio
+options:
+ - "Copper"
+ - "Aluminum"
+```
−## Infrared Scanning Provisions {toc}
+### Copper bus carries more current per unit cross-section, has the lower contact resistance at a bolted joint, and costs more; aluminum bus is lighter and less expensive for the same rating, and its joints depend on the plating and on the joint hardware to hold their resistance through thermal cycling, which is why aluminum is chosen where the cost difference on a large bus matters and copper is chosen where the joint count is high, where the bus is to be field-extended, or where the environment attacks aluminum. {note}
−### Enclosure shall include removable infrared inspection windows or cover plates at the main device, bus joints between sections, and feeder breaker line-side connections.
+### Where copper bus is selected, it shall be copper bus bar conforming to ASTM B187 with a conductivity of not less than 98% IACS.
−### Infrared inspection windows shall allow thermographic inspection of energized connections without removing covers or de-energizing the equipment.
+### Where aluminum bus is selected, it shall be an aluminum alloy bus conductor conforming to ASTM B317 with a conductivity of not less than 55% IACS, and shall be plated over its full length.
−# Circuit Breakers {toc}
+### A joint between an aluminum bus and a copper conductor, terminal, or bus shall be made with a connector or a plated joint listed for the combination.
−## Main Device {toc}
+## Bus Plating {toc}
−### The main device configuration shall be as indicated in the datasheet.
+### The bus plating shall be as indicated in the datasheet.
```datasheet
−label: Main Device Configuration
−type: select
−drawing_ref: "one-line diagram"
+label: Bus Plating
+type: radio
options:
− - "Main circuit breaker"
− - "Main fusible switch"
− - "Main lugs only (no main device)"
− - "Through-bus (sub-feed, no main device)"
−default: deferred
+ - "Unplated, with plated joint contact surfaces"
+ - "Tin-plated over the full length"
+ - "Silver-plated over the full length"
+default: manufacturer
```
−### The main breaker construction shall be as indicated in the datasheet.
+### The manufacturer shall state the plating in the product data.
+### Bare copper bus with plating at the joints holds its contact resistance in a clean, dry interior and is the construction most copper switchboards are built with; tin plating over the full length resists the sulfur compounds that blacken silver and raise its contact resistance, and is the plating that holds its resistance where the atmosphere carries hydrogen sulfide, as in a wastewater facility; silver plating has the lowest contact resistance in a clean atmosphere. Aluminum bus is plated in every construction because its oxide forms within minutes of exposure and is an insulator. {note}
+
+### Plating shall be continuous over every bolted joint contact surface, every device line and load connection, and every splice at a shipping split.
+
+## Bus Sizing Basis {toc}
+
+### The basis on which the bus cross-section is sized shall be as indicated in the datasheet.
+
```datasheet
−label: Main Breaker Type
+label: Bus Sizing Basis
type: select
options:
− - "Molded-case circuit breaker (MCCB), fixed-mounted"
− - "Insulated-case circuit breaker (ICCB), fixed-mounted"
− - "Insulated-case circuit breaker (ICCB), individually drawout"
+ - "Temperature rise per UL 891"
+ - "Current density not exceeding 1000 A per square inch of copper"
+ - "Current density not exceeding 750 A per square inch of copper"
+default: "Temperature rise per UL 891"
```
−### The main breaker trip unit shall be as indicated in the datasheet.
+### UL 891 sizes the bus so that its temperature rise under rated current does not exceed 65 °C over a 40 °C ambient, and that is the basis every listed switchboard is built to and the basis the manufacturer applies unless told otherwise; a density limit of 1000 A per square inch of copper gives a bus near the UL 891 rise in most sections and a larger bus in the compact ones; a limit of 750 A per square inch gives a cooler bus with more margin for an elevated room ambient, a future load increase, or harmonic heating, at the cost of more copper and sometimes a deeper section. {note}
+### Where a current density basis is selected for a copper bus, the equivalent density for an aluminum bus shall be the selected value multiplied by the ratio of the aluminum conductivity to the copper conductivity, and the manufacturer shall show the resulting bus cross-section on the shop drawings.
+
+## Bus Insulation {toc}
+
+### The bus insulation shall be as indicated in the datasheet.
+
```datasheet
−label: Main Breaker Trip Unit
−type: select
+label: Bus Insulation
+type: radio
options:
− - "Thermal-magnetic (available on smaller frames)"
− - "Electronic trip - LSI (Long-time, Short-time, Instantaneous)"
− - "Electronic trip - LSIG (Long-time, Short-time, Instantaneous, Ground Fault)"
−default: "Electronic trip - LSIG (Long-time, Short-time, Instantaneous, Ground Fault)"
+ - "Bare bus with isolating barriers"
+ - "Insulated bus with flame-retardant sleeving or coating"
+default: "Bare bus with isolating barriers"
```
−### Main lugs only configurations are limited to NFPA 70 Article 408.36 requirements (maximum six service disconnects, where applicable).
+### Bare bus behind barriers is the construction most switchboards are built with; insulated bus covers every bus surface a dropped tool or a misplaced hand could reach with a cover off, and reduces the chance that an arcing fault started at one point propagates along the bus, at the cost of the insulation and of the heat it holds in, which can call for a larger bus for the same rating. {note}
−### Through-bus configurations require coordination with the upstream device for overcurrent protection of the switchboard bus.
+### Where insulated bus is selected, the insulation shall be flame-retardant, shall be rated for the system voltage, and shall be continuous through the barriers and the bus transitions between sections, with the joints covered by removable insulating boots.
−### Insulated-case circuit breakers (ICCBs) are recommended for mains 1200A and larger because they provide a short-time withstand rating that allows selective coordination with downstream devices. {note}
+## Bus Arrangement, Joints, and Bracing {toc}
−### Drawout ICCB mains are used where the main must be serviced or replaced without de-energizing the upstream source. {note}
+### The phase bus shall be arranged so that the phase sequence is A, B, C from front to back, top to bottom, or left to right as viewed from the front, in accordance with NFPA 70 408.3(E).
−### Main breaker frame size and trip rating shall be [[drawing: as indicated on the one-line diagram]].
+### The bus shall be supported on insulating supports that withstand the bus short-circuit bracing indicated in the datasheet without damage, and the bus and its supports shall be rated for the system voltage.
−### LSIG trip units are recommended for main devices on solidly grounded wye systems. {note}
+### Bus joints shall be bolted with hardware that maintains contact pressure through thermal cycling, and the joint hardware and torque shall be those established under the listing.
−### Ground fault protection is required by NFPA 70 Article 230.95 for solidly grounded wye services over 150V to ground rated 1000A or more, and by Article 215.10 for feeders meeting the same criteria.
+### The bus shall be spliced at every shipping split by a bolted splice plate furnished by the manufacturer, and the splice shall carry the full rating of the bus it joins.
−### Even where not code-required, ground fault protection significantly reduces equipment damage from arcing faults. {note}
+### Bus joints shall be accessible for inspection and re-torquing from the front of the switchboard, or from the rear where the switchboard is rear-accessible, without removing a device.
−## Feeder Devices {toc}
+## Bus Extension Provisions {toc}
−### Feeder device quantities shall be [[drawing: as indicated on the one-line diagram]].
+### The provisions for future extension of the switchboard shall be as indicated in the datasheet.
−### Feeder device frame sizes and trip ratings shall be [[drawing: as indicated on the breaker schedule]].
−
−### The feeder device type shall be as indicated in the datasheet.
−
```datasheet
−label: Feeder Device Type
+label: Bus Extension Provisions
type: select
options:
− - "Molded-case circuit breakers (MCCB), group-mounted"
− - "Molded-case circuit breakers (MCCB), individually mounted"
− - "Insulated-case circuit breakers (ICCB), group-mounted"
− - "Fusible switches (group-mounted)"
−default: "Molded-case circuit breakers (MCCB), group-mounted"
+ - "No extension provisions"
+ - "Extension provisions at one end"
+ - "Extension provisions at both ends"
+default: "No extension provisions"
```
−### The feeder breaker trip units shall be as indicated in the datasheet.
+### Extension provisions consist of a removable end closure, phase bus ends drilled for a splice, and neutral and ground bus ends drilled to match, so that a section can be added without drilling live bus; most switchboards are built against a wall or an end of the room with no section to come, which is why none is the default, and a lineup that is expected to grow carries the provisions at the end that will remain open. {note}
+### Where extension provisions are furnished, the end at which they are furnished shall be as indicated on [[drawing: the electrical plans]], and the through-bus to that end shall carry the rating the extension is to be made at.
+
+# Structure and Enclosure {toc}
+
+## Enclosure Type {toc}
+
+### The enclosure type shall be as indicated in the datasheet.
+
```datasheet
−label: Feeder Breaker Trip Units
+label: Enclosure Type per NEMA 250
type: select
−drawing_ref: "breaker schedule"
options:
− - "Thermal-magnetic (all feeders)"
− - "Electronic trip - LSI (all feeders)"
− - "Electronic trip - LSIG (all feeders)"
−default: deferred
+ - "Type 1"
+ - "Type 1 gasketed"
+ - "Type 2"
+ - "Type 3R"
+ - "Type 4"
+ - "Type 4X"
+ - "Type 12"
+default: "Type 1"
```
−### Group-mounted feeder devices are the most common configuration and provide the highest device density. {note}
+### A dry, conditioned electrical room is the installed location on most projects, which is why Type 1 is the default; every other location named in the clauses of this article calls for the type those clauses require. {note}
−### Individually mounted devices are used for larger frames (typically 800A and above) or where compartmentalization between feeders is required. {note}
+### The enclosure shall comply with UL 50 and, for a type other than Type 1, with UL 50E and NEMA 250 for the type selected, and the type shall be marked on the structure.
−### Electronic trip units shall be specified for feeders 400A and larger to allow adjustable settings for selective coordination.
+### A switchboard installed outdoors shall have an enclosure of Type 3R, Type 4, or Type 4X, with rain hoods over ventilation openings and a drip shield over each door.
−### Thermal-magnetic breakers are acceptable for smaller feeders where coordination is not critical.
+### A switchboard installed where it is subject to hose-directed water or wash-down shall have an enclosure of Type 4 or Type 4X.
−## Selective Coordination {toc}
+### A switchboard installed where the atmosphere carries salt, chemical vapor, or another corrosive agent, including a coastal site, a wastewater facility, and a food-processing area, shall have a Type 4X enclosure.
−### See [[sync/protective-coordination-study]] for coordination study requirements. {note}
+### A switchboard installed indoors where airborne dust, lint, or fibers accumulate shall have an enclosure of Type 12, Type 1 gasketed, Type 4, or Type 4X.
−### The selective coordination requirement shall be as indicated in the datasheet.
+### A switchboard installed indoors where dripping or light splashing of a non-corrosive liquid occurs shall have an enclosure of Type 2, Type 12, Type 4, or Type 4X.
+### Where a rating higher than the datasheet selection is required by the clauses of this article for the installed location, the higher rating shall be furnished and the conflict reported to the Engineer of Record before the switchboard is released for manufacture.
+
+### A field opening cut in a Type 3R, Type 4, Type 4X, or Type 12 structure other than at a location and by a method the listing permits removes the environmental rating, and the rework is charged to the party that made the cut. {note}
+
+### Where the switchboard is installed outdoors, the outdoor housing arrangement shall be as indicated in the datasheet.
+
```datasheet
−label: Selective Coordination Required
+label: Outdoor Housing Arrangement
type: radio
options:
− - "Required - emergency or critical system per NFPA 70"
− - "Required - Owner standard"
− - "Not required"
−default: "Not required"
+ - "Non-walk-in"
+ - "Walk-in aisle"
+default: "Non-walk-in"
```
−### Where required by NFPA 70 (for example, Articles 700.32, 701.27, and 708.54 for emergency, legally required standby, and critical operations power systems, respectively), feeder and main devices shall be selectively coordinated for the full range of available overcurrents and time durations.
+### A non-walk-in housing is the smaller and lighter structure and the one most outdoor switchboards are built as, and its working space is the outdoor pad in front of it; a walk-in housing puts the working space inside a weatherproof room so that a device can be serviced in any weather, at the cost of a larger and heavier structure. {note}
−### Coordination shall be demonstrated by time-current curves overlaid on a common log-log plot.
+### Where a walk-in housing is furnished, the aisle shall provide the working space required by NFPA 70 110.26 in front of every device, and the housing shall have lighting, a convenience receptacle, and a door openable from inside without a key.
−## Breaker Accessories {toc}
+## Enclosure Material and Finish {toc}
−### Breaker accessories shall be furnished as indicated in the datasheet.
+### The enclosure material shall be as indicated in the datasheet.
```datasheet
−label: Breaker Accessories
−type: checkbox
+label: Enclosure Material
+type: select
options:
− - "Auxiliary contacts (1a + 1b minimum)"
− - "Shunt trip"
− - "Undervoltage release"
− - "Bell alarm contact"
− - "Mechanical interlock (paired breakers)"
− - "Kirk key interlock"
− - "Motor operator with remote close/trip"
− - "Padlock provisions (open position)"
−default: "Auxiliary contacts (1a + 1b minimum)"
+ - "Painted steel"
+ - "Type 304 stainless steel"
+ - "Type 316 stainless steel"
+default: "Painted steel"
```
−### Auxiliary contacts shall be provided on every device that participates in a control or status circuit.
+### Painted steel is the construction the switchboard is built with and serves every enclosure type in a non-corrosive exposure; stainless steel is what a Type 4X rating is built in, with Type 316 holding up where chlorides are present. {note}
−### All accessories on a given breaker shall be the manufacturer's standard catalog options for that frame.
+### Where the datasheet selects a Type 4X enclosure, the enclosure material shall be one for which the Type 4X rating is listed.
−### Field-installed accessories that void the listing are not acceptable.
+### Structural members shall be steel of not less than 12 gauge, and doors and covers shall be steel of not less than 14 gauge, formed and reinforced so that a door or cover does not deflect when opened or removed with its devices installed.
−# Protective Relaying {toc}
+### A painted steel enclosure shall carry a baked powder coat or enamel finish over a phosphate pretreatment, and the manufacturer shall state the finish system and its dry film thickness in the product data.
−## Where discrete protective relays are applied, the protection functions shall be as indicated in the datasheet.
+### The finish color shall be as indicated in the datasheet.
```datasheet
−label: Protective Relay Functions
+label: Finish Color
+type: select
+options:
+ - "ANSI 61 light gray"
+ - "ANSI 49 medium gray"
+ - "ANSI 70 sky gray"
+ - "Custom color matched to a sample furnished by the Owner"
+default: "ANSI 61 light gray"
+```
+
+### ANSI 61 is the color the equipment is finished in unless told otherwise and the one the other electrical equipment on a project most often matches; the other grays and a custom color are chosen to match existing equipment in the room or an Owner's standard. {note}
+
+## Section Arrangement and Accessibility {toc}
+
+### The accessibility of the switchboard shall be as indicated in the datasheet.
+
+```datasheet
+label: Section Accessibility
+type: select
+options:
+ - "Front-accessible, front-connected"
+ - "Rear-accessible, rear-connected"
+ - "Front- and rear-accessible"
+```
+
+### A front-accessible switchboard makes every bus joint and every device connection from the front, stands against a wall, and needs working space on one face only, which is the construction the smaller bus ratings are built as; a rear-accessible switchboard lands the main and feeder conductors on the back of the devices, which gives the large conductor bundles of a high-rated service the bending space they need and keeps the cable away from the operating face, at the cost of a rear working space the room has to provide; a front- and rear-accessible switchboard is the rear-connected construction with the device fronts also serviceable, which is what a switchboard that sits in the open with aisles on both faces is built as. The choice follows the bus rating, the conductor count at the main, and the room, so the field asserts no default. {note}
+
+### Where a rear-accessible or a front- and rear-accessible switchboard is furnished, the rear shall be closed by hinged doors or bolted covers over every section, and the working space behind the switchboard shall be as NFPA 70 110.26 requires for the condition.
+
+### Sections shall be of uniform height and depth across the switchboard, shall align flush at the front, and shall be bolted together to form a rigid continuous assembly.
+
+### The number of vertical sections shall be the number needed to house the devices on the one-line diagram with the spare and space provisions this standard requires, and shall be shown on the shop drawings.
+
+### Section height and depth shall be the manufacturer's standard for the largest device installed and the accessibility selected, and shall be shown on the shop drawings.
+
+### The device covers shall be as indicated in the datasheet.
+
+```datasheet
+label: Device Covers
+type: radio
+options:
+ - "Hinged covers over bolted dead-front"
+ - "Bolted removable covers"
+```
+
+### A hinged cover swings open on its own hinges so that the device line and load connections behind it can be inspected or re-torqued by one person without a cover to set down, and it is closed with a tool so that the dead-front stays in place during operation; a bolted removable cover costs less and is the construction the smaller switchboards are built with, and each inspection means a cover lifted off and set aside with the bus behind it exposed. {note}
+
+### Every device handle shall be operable with the device cover closed, and no energized part shall be exposed with the covers in place and the doors closed.
+
+## Internal Barriers {toc}
+
+### The internal barriers furnished within the structure shall be as indicated in the datasheet.
+
+```datasheet
+label: Internal Barriers
type: checkbox
options:
− - "Overcurrent (50/51)"
− - "Ground fault (50G/51G)"
− - "Under/overvoltage (27/59)"
− - "Under/overfrequency (81)"
− - "Reverse power (32)"
− - "Phase reversal (47)"
+ - "Barrier between the main bus compartment and the device compartments"
+ - "Barrier isolating the main section from the distribution sections"
+ - "Barriers between the line-side connections of adjacent individually mounted devices"
+ - "Barrier isolating the utility metering compartment"
+ - "Barrier isolating the surge protective device compartment"
default:
− - "Ground fault (50G/51G)"
+ - "Barrier between the main bus compartment and the device compartments"
```
−## Relay settings shall be [[drawing: as indicated on the relay setting schedule]].
+### A barrier between the bus and the devices is what keeps a worker at a device cover away from the through-bus and is the one every switchboard is built with; a barrier at the main section keeps a fault in the distribution sections from the main and its line-side connections; barriers between individually mounted devices let one be worked on with its neighbors energized; the metering and surge protective device barriers keep those compartments, which are opened by different people for different reasons, away from the bus and the device connections. Each barrier adds cost and section depth, and each reduces what a worker can reach with a cover off. {note}
−## Discrete protective relays in switchboards are typically limited to ground fault protection for the main device and any specialized functions for generator paralleling, utility intertie, or co-generation applications. {note}
+### Barriers shall be grounded metal or an insulating material rated for the system voltage, and a barrier required by the listing or by NFPA 70 230.71(B) shall be furnished whatever the datasheet selects.
−## Where applied, relays shall be microprocessor-based with digital displays, self-diagnostics, and event recording.
+## Conduit Entry and Wiring Space {toc}
−## Where applied, relays shall be tested per IEEE C37.90.1 for surge withstand capability.
+### Conduit entry to the switchboard shall be as indicated in the datasheet.
−# Metering and Instrumentation {toc}
+```datasheet
+label: Conduit Entry
+type: radio
+drawing_ref: "the electrical plans"
+options:
+ - "Top entry"
+ - "Bottom entry"
+ - "Top and bottom entry"
+default: deferred
+```
−## Instrument Transformers {toc}
+### Conduit shall enter only through the areas designated on the shop drawings, and the bus compartments, the device compartments, and the barriers between them shall not be penetrated by a raceway.
−### Current transformers shall comply with IEEE C57.13.
+### The wiring space at every device shall satisfy the bending space NFPA 70 312.6 requires for the conductors indicated on the one-line diagram, and where the standard section does not provide it the manufacturer shall furnish a deeper or wider section, or a pull section, and shall show the wiring space on the shop drawings.
−### Accuracy class shall be appropriate for the connected metering function:
+### Where a busway terminates at the switchboard, the busway flange, the bus connection, and the barrier at the entry shall be furnished by the switchboard manufacturer under the assembly listing, located as indicated on [[drawing: the electrical plans]], and matched to the busway furnished under [[sync/busway]].
−- Revenue metering: Class 0.3 accuracy
−- Protective relaying: Class C200 or higher
−- General monitoring: Class 0.6 accuracy
+### Where a wireway or an auxiliary gutter adjoins the switchboard, the connection shall be made through the wiring space the manufacturer designates on the shop drawings with a coupling listed for the connection, and the trough shall comply with [[sync/wireways-and-auxiliary-gutters]].
−### Current transformers for metering and relaying shall be provided on separate cores.
+### A structure in a Type 3R, Type 4, or Type 4X enclosure shall be entered only with hubs or fittings listed for the enclosure type, and every unused opening shall be closed with a fitting listed for the type.
−### CTs shall not be shared between metering and protection functions.
+# Arc-Flash Mitigation and Maintenance Safety {toc}
−### Where the switchboard serves as utility service equipment, the utility CT compartment shall be sized and located per the serving utility's standards and shall be sealable.
+## Arc-Resistant Construction {toc}
−## Power Monitoring {toc}
+### Arc-resistant construction shall be as indicated in the datasheet.
−### The metering provided at the switchboard shall be as indicated in the datasheet.
−
```datasheet
−label: Metering Type
+label: Arc-Resistant Construction
type: select
options:
− - "No metering"
− - "Analog ammeter and voltmeter with phase selector switches"
− - "Digital multifunction meter at the main"
− - "Digital multifunction meter at the main and each feeder"
− - "Revenue-grade metering per utility requirements"
−default: "Digital multifunction meter at the main"
+ - "Not required"
+ - "Type 1 accessibility per IEEE C37.20.7"
+ - "Type 2 accessibility per IEEE C37.20.7"
```
−### The metered quantities and recording functions shall be as indicated in the datasheet.
+### Arc-resistant construction directs the products of an internal arcing fault away from the front of the switchboard, and Type 2 extends that protection to the sides and rear. It protects a worker standing at the switchboard during an arcing fault with the doors closed and latched, and it adds a plenum, reinforced doors, and pressure-relief flaps that raise the height and the cost of every section, which is why most switchboards are built without it and a project whose arc-flash study or whose operating practice calls for workers at the energized switchboard buys it. {note}
+### Where arc-resistant construction is selected, the switchboard shall have been tested to IEEE C37.20.7 in the configuration furnished at the assembly short-circuit current rating and the short-time withstand duration selected, and the exhaust plenum and its discharge location shall be shown on the shop drawings.
+
+### Arc-resistant construction does not lower the incident energy at a device whose cover is open, and does not substitute for the arc energy reduction required by NFPA 70 240.87. {note}
+
+## Maintenance Safety Provisions {toc}
+
+### The maintenance safety provisions furnished shall be as indicated in the datasheet.
+
```datasheet
−label: Meter Functions
+label: Maintenance Safety Provisions
type: checkbox
options:
− - "Voltage (L-L, L-N all phases)"
− - "Current (per phase and neutral)"
− - "Power factor (per phase and total)"
− - "kW / kVA / kVAR (demand and instantaneous)"
− - "kWh / kVARh energy accumulation"
− - "Harmonics (THD per phase, individual to 31st)"
− - "Min/max recording with time stamp"
− - "Waveform capture"
−default:
− - "Voltage (L-L, L-N all phases)"
− - "Current (per phase and neutral)"
− - "Power factor (per phase and total)"
− - "kW / kVA / kVAR (demand and instantaneous)"
− - "kWh / kVARh energy accumulation"
− - "Min/max recording with time stamp"
+ - "Infrared inspection windows at the main connections and the bus splices"
+ - "Voltage presence indicator at each section"
+ - "Absence-of-voltage tester at the main device"
+ - "Remote operator for the main device"
+ - "Remote racking device for a drawout-mounted main"
```
−### Where a meter is provided, its communication protocol shall be as indicated in the datasheet and shall be supported by the Owner's building management system.
+### Each provision lets a task be performed with less exposure than the alternative: an infrared window lets a connection be scanned under load with the cover on, a voltage indicator confirms the state of a section before its cover is removed, an absence-of-voltage tester verifies a de-energized state without a handheld meter, a remote operator lets the main be closed from outside the arc-flash boundary, and a remote racking device lets a drawout main be racked with the operator outside the boundary. {note}
+### Arc-flash warning labels shall be applied to each section in accordance with NFPA 70 110.16 and NFPA 70E, with the values taken from the study performed under [[sync/arc-flash-study]], placed so that each is read before a cover is removed or a door opened.
+
+# Service Entrance, Surge Protection, and Metering Provisions {toc}
+
+## Utility Metering Compartment {toc}
+
+### The utility metering compartment shall be as indicated in the datasheet.
+
```datasheet
−label: Metering Communication Protocol
+label: Utility Metering Compartment
type: select
+derived: "the service configuration and the serving utility's metering requirements as confirmed in writing"
options:
− - "No communications"
− - "Modbus RTU (RS-485)"
− - "Modbus TCP/IP (Ethernet)"
− - "BACnet IP"
− - "DNP3"
+ - "Not furnished"
+ - "Utility current transformer compartment ahead of the main, cold sequence"
+ - "Utility current transformer compartment after the main, hot sequence"
+default: derived
```
−### Where building energy code requires submetering (ASHRAE 90.1 Section 8.4 or local amendments), meter data shall be accessible via the selected communication protocol for integration with the building management system.
+### Whether a utility compartment is furnished follows from whether the switchboard is service equipment, and whether the utility's transformers sit ahead of the main or after it follows from the serving utility's metering rules, so the field records the consequence of those inputs; a cold-sequence compartment is de-energized by the service disconnect so that the utility can work in it without a utility-side disconnect, and a hot-sequence compartment is energized ahead of any customer device so that the main cannot be used to interrupt the metering. {note}
−### Coordinate communication wiring and protocols with [[sync/building-automation-system]].
+### Where a utility metering compartment is furnished, it shall be sized, arranged, barriered, and provided with sealing provisions in accordance with the serving utility's published requirements, and the utility's current transformers and meter shall be mounted on provisions the switchboard manufacturer furnishes.
−# Surge Protection {toc}
+### Where a utility metering compartment is furnished, it shall be separated from every other compartment by a barrier and shall be accessible only through its own cover or door.
−## Whether a surge protective device is provided at the switchboard shall be as indicated in the datasheet.
+## Surge Protective Device Provisions {toc}
+### A surge protective device shall be furnished at the switchboards indicated on [[drawing: the one-line diagram]], and the device, its type, its ratings, its protection modes, and its lead length shall comply with [[sync/surge-protective-devices]].
+
+### Where a surge protective device is furnished at a switchboard, its mounting arrangement shall be as indicated in the datasheet.
+
```datasheet
−label: Surge Protective Device (SPD)
+label: Surge Protective Device Mounting Arrangement
type: radio
options:
− - "Provided"
− - "Not provided"
−default: "Provided"
+ - "Integral, factory-installed in a compartment of the switchboard"
+ - "External, mounted adjacent to the switchboard and connected through a dedicated feeder device"
```
−## The SPD type shall be as indicated in the datasheet.
+### An integral device is connected to the bus by the manufacturer with the shortest lead the structure allows, is covered by the assembly listing, and is replaced from within the switchboard; an external device is connected through a feeder device with a lead of whatever length the installation produces, is replaced without opening the switchboard, and is the arrangement used where the switchboard is existing or where the Owner standardizes on one device family across equipment of several makers. {note}
+### Where an integral surge protective device is furnished, it shall be listed to UL 1449, shall be installed by the switchboard manufacturer under the UL 891 listing, shall be connected to the bus through a dedicated disconnect so that it can be isolated for replacement without de-energizing the switchboard, and shall have its status indication visible with the cover closed.
+
+### Where the switchboard is service equipment, the surge protective device at it is the service-equipment surge protection that [[sync/lightning-protection]] coordinates with, and its connection to the grounding electrode system shall be as [[sync/grounding-and-bonding]] requires.
+
+## Metering Provisions {toc}
+
+### The metering furnished within the switchboard shall be as indicated in the datasheet.
+
```datasheet
−label: SPD Type
+label: Metering Provisions
type: select
options:
− - "Type 1 - permanently connected on the line side of the service disconnect"
− - "Type 2 - permanently connected on the load side of the service disconnect"
− - "Type 1+2 combination (line-side and load-side protection in one assembly)"
−default: "Type 2 - permanently connected on the load side of the service disconnect"
+ - "No metering"
+ - "Current transformer and meter mounting provisions only"
+ - "Main metering"
+ - "Main and feeder metering"
```
−## The SPD nominal discharge current rating shall be as indicated in the datasheet.
+### Main metering records the switchboard as one load, which is what a service or a tenant main needs for demand and energy; feeder metering makes each feeder visible for commissioning, submetering, and measurement and verification, at the cost of current transformers on every feeder and a meter able to read them; mounting provisions leave the compartment and the current transformer space in place for a meter bought later. Whether a switchboard carries any meter depends on what the monitoring system under [[sync/electrical-power-monitoring]] wants from it, so the field asserts no default. {note}
+### Meters, their accuracy class, their current transformers, and their communications shall comply with [[sync/electrical-power-monitoring]], and where metering is furnished within the switchboard it shall be installed by the manufacturer under the UL 891 listing in an instrument compartment separate from the wiring space and the bus.
+
+### Current transformers furnished within the switchboard shall comply with IEEE C57.13, and current transformers serving a protective relay shall be on cores separate from those serving a meter.
+
+### Where [[parameter: adopted-energy-code]] requires the loads served from the switchboard to be submetered, the metering shall accumulate energy for those loads and shall report it to the building energy monitoring system under [[sync/electrical-power-monitoring]].
+
+## Protective Relays {toc}
+
+### Where the one-line diagram indicates a protective relay at the switchboard other than the ground-fault relay furnished under Ground-Fault Protection of Equipment, the relay, its current and voltage transformers, and its control wiring shall be furnished and installed by the switchboard manufacturer under the assembly listing, and the relay settings shall be as established under [[sync/protective-coordination-study]].
+
+### A discrete relay at a switchboard is the exception rather than the rule, and it appears where the switchboard takes a generator or a second source and needs the under- and overvoltage, frequency, reverse-power, or phase-sequence functions a trip unit does not carry. {note}
+
+# Communications {toc}
+
+## Network Protocol {toc}
+
+### The communications protocol of the switchboard network shall be as indicated in the datasheet.
+
```datasheet
−label: SPD Nominal Discharge Current (In)
−type: range
−unit: kA
+label: Communications Protocol
+type: select
options:
− min: 10
− max: 40
− setpoints: [10, 20, 40]
−default: 20
+ - "No network"
+ - "Modbus RTU"
+ - "Modbus TCP"
+ - "BACnet/IP"
+ - "BACnet MS/TP"
+ - "EtherNet/IP"
+ - "DNP3"
```
−## For service entrance switchboards, NFPA 70 Article 230.67 requires a surge protective device for dwelling unit services and certain other occupancies. {note}
+### The protocol has to match the system the switchboard reports to: a switchboard whose meters and trip units report to the building automation system speaks the protocol that system reads, which is settled under [[sync/building-automation-system]], and one reporting to a power monitoring system speaks what that system reads under [[sync/electrical-power-monitoring]]; the serial protocols run on a two-wire bus and cost least, the Ethernet protocols carry more data and allow the trip units to be read and the maintenance switch status to be seen remotely, and DNP3 is the protocol a utility or a generation control system reads. {note}
−## SPDs in switchboards shall be UL 1449 listed, integral to the assembly with a dedicated SPD disconnect, and located as close as practical to the bus connection point to minimize lead length.
+### Where a network is furnished, the devices connected to it shall be as indicated in the datasheet.
−## Indicating lights and dry contacts shall be provided for remote status monitoring.
+```datasheet
+label: Networked Devices
+type: checkbox
+options:
+ - "Meters"
+ - "Main circuit breaker trip unit"
+ - "Feeder circuit breaker trip units"
+ - "Ground-fault relay"
+ - "Surge protective device status contacts"
+ - "Energy-reducing maintenance switch status"
+```
−# Finish and Identification {toc}
+### Where a network is furnished, the network cable, the gateways, the terminations, and the power supplies for the network shall be installed by the manufacturer within the switchboard, and the network shall be brought to a terminal or a connector in a designated compartment for the field connection.
−## The enclosure finish color shall be as indicated in the datasheet.
+### Network cable inside the switchboard shall be routed separately from the power conductors and the bus, and where it must cross a power conductor it shall cross at a right angle.
−```datasheet
−label: Finish Color
−type: text
−default: "ANSI 49 light gray"
−```
+### Each networked device shall be assigned an address on the network address list submitted with the action submittals, and the address shall be marked at the device.
−## Enclosure shall receive a minimum two-coat paint system: corrosion-resistant primer and manufacturer's standard polyester powder coat finish.
+# Identification {toc}
−## Minimum total dry film thickness shall be 3 mils (75 microns).
+## Nameplates, arc-flash warning labels, available fault current markings, and source identification shall comply with [[sync/equipment-labeling]] for material, lettering, attachment, and content, and the text shall be that listed on the nameplate schedule.
−## For outdoor installations or environments classified C3 or higher, an enhanced paint system with a minimum of 5 mils dry film thickness shall be applied.
+## Each switchboard shall carry an assembly nameplate stating the switchboard designation, the system voltage with the number of phases and wires, the main bus rating, the main device rating where one is furnished, the assembly short-circuit current rating, the short-time withstand rating where one is furnished, and the source that feeds it.
−## Labeling {toc}
+## Each device shall carry a nameplate stating the device designation, the frame size and trip rating or the switch and fuse rating, and the load served, and the designation shall match the designation on the one-line diagram.
−### Manufacturer shall provide engraved nameplates for the switchboard assembly and each individual device.
+## The manufacturer shall mark on the structure the UL 891 listing, the series-rated combinations where series rating is the basis, and the devices listed for installation in each position.
−### Nameplates shall identify:
+## Where the switchboard is fed from a source that is not within sight, the location of that source and its circuit designation shall be marked on the switchboard in accordance with NFPA 70 408.4(B), and where more than one source feeds the switchboard each shall be identified at the switchboard.
−- Switchboard designation and one-line reference
−- Bus ratings (voltage, continuous current, short-circuit)
−- Individual breaker designation, frame size, and trip rating
−- Current transformer ratios and accuracy class
−- Arc flash warning labels per NFPA 70E and IEEE 1584
−- Available fault current and date of calculation per NFPA 70 Article 110.24 (service equipment)
+## The available fault current at the line terminals and the date it was calculated shall be field-marked on each switchboard that is service equipment, in accordance with NFPA 70 110.24.
−### The nameplate material shall be as indicated in the datasheet.
+## Where the switchboard serves an emergency, legally required standby, or critical operations power system, it shall be marked as a component of that system in accordance with the article of NFPA 70 that governs the system.
+## Whether a mimic bus is furnished shall be as indicated in the datasheet.
+
```datasheet
−label: Nameplate Material
+label: Mimic Bus
type: radio
options:
− - "Laminated phenolic (indoor)"
− - "Stainless steel (outdoor or corrosive)"
− - "Aluminum (anodized)"
−default: "Laminated phenolic (indoor)"
+ - "Not furnished"
+ - "Furnished"
+default: "Not furnished"
```
−### Equipment labeling shall follow [[sync/equipment-labeling]] conventions.
+## A mimic bus is a colored line drawn on the front of the switchboard that traces the bus and the devices as the one-line diagram does, so that an operator can see which device feeds what without reading the nameplates; it earns its cost on a main-tie-main or a multi-source switchboard whose operation depends on the operator understanding the arrangement, and most single-main switchboards are built without one. {note}
−### Where the switchboard supplies emergency, legally required standby, or critical operations loads, additional identification per NFPA 70 Articles 700.10, 701.10, and 708.10 shall be provided.
−
# Testing {toc}
−## Factory Production Tests {toc}
+## Factory Tests {toc}
−### The manufacturer shall perform the following production tests on the completed switchboard assembly per UL 891 and NEMA PB 2:
+### The manufacturer shall perform the production tests of UL 891 and NEMA PB 2 on every switchboard before shipment, including a dielectric withstand test of the bus, a continuity check of every control, metering, and ground-fault circuit against the schematic diagrams, a mechanical operation check of every device and interlock, an inspection of every bus joint against the listed torque, and an inspection of the assembly against the reviewed shop drawings.
−- 60 Hz dielectric withstand test on primary bus (phase-to-phase and phase-to-ground)
−- Insulation resistance measurement on each phase and neutral bus
−- Mechanical operation of each circuit breaker (minimum three open/close cycles)
−- Ground fault sensing system functional test (where applicable)
−- Control wiring continuity verification per the approved schematics
−- Current transformer ratio and polarity test
−- Visual and dimensional inspection against approved shop drawings
+### Factory test witnessing shall be as indicated in the datasheet.
−### Factory acceptance test witnessing shall be as indicated in the datasheet.
−
```datasheet
−label: Factory Acceptance Test
+label: Factory Test Witnessing
type: radio
options:
− - "Witnessed by Owner's representative"
− - "Unwitnessed with certified test report"
− - "Not required beyond standard production tests"
−default: "Unwitnessed with certified test report"
+ - "Witnessed by the Owner's representative"
+ - "Certified test report without witnessing"
+default: "Certified test report without witnessing"
```
−### Where witnessed factory testing is specified, the manufacturer shall provide a minimum of two weeks advance notice of test readiness.
+### Where witnessing is selected, the manufacturer shall give not less than two weeks' notice of test readiness, shall submit the test procedure for review before the test, and shall not ship a switchboard until the witness has accepted the results or has waived attendance in writing.
−### Where witnessed factory testing is specified, test procedures shall be submitted for review prior to testing.
+### A witnessed test lets the Owner see every device operate and every interlock work before the switchboard ships, and it commits a representative to a trip to the factory for each shipment; a certified report records the same tests without the trip, and leaves any discrepancy to be found at field acceptance testing. {note}
−# Field Quality Control {toc}
−
## Field Acceptance Tests {toc}
−### Contractor shall engage a qualified independent testing firm to perform acceptance testing per NETA ATS Section 7.1 (switchboards) and Section 7.6 (low voltage circuit breakers).
+### Field acceptance tests shall be performed on every switchboard after installation is complete and before it is energized, in accordance with ANSI/NETA ATS and [[sync/electrical-acceptance-testing]], and shall include the tests indicated in the datasheet.
−### Field acceptance tests shall include as a minimum:
+```datasheet
+label: Field Acceptance Tests
+type: checkbox
+options:
+ - "Visual and mechanical inspection including anchorage, nameplates, clearances, barriers, and covers"
+ - "Bolted connection torque verification against the manufacturer's values, with the applied values recorded"
+ - "Insulation resistance of each phase bus and the neutral bus, phase-to-phase and phase-to-ground"
+ - "Contact resistance of the bus splices and the main and feeder terminations"
+ - "Operation of every device through one open and close cycle, and of every drawout device through every position"
+ - "Primary current injection of every electronic trip unit at one point per function"
+ - "Ground-fault protection of equipment performance test by primary current injection"
+ - "Trip unit and relay settings verification against the coordination study"
+ - "Shunt trip, undervoltage release, and interlock operation from the initiating device"
+ - "Current transformer ratio and polarity verification"
+ - "Meter and network function verification against the point list"
+ - "Neutral-to-ground separation verification on every switchboard that is not service equipment"
+default:
+ - "Visual and mechanical inspection including anchorage, nameplates, clearances, barriers, and covers"
+ - "Bolted connection torque verification against the manufacturer's values, with the applied values recorded"
+ - "Insulation resistance of each phase bus and the neutral bus, phase-to-phase and phase-to-ground"
+ - "Contact resistance of the bus splices and the main and feeder terminations"
+ - "Operation of every device through one open and close cycle, and of every drawout device through every position"
+ - "Trip unit and relay settings verification against the coordination study"
+ - "Neutral-to-ground separation verification on every switchboard that is not service equipment"
+```
−- Visual and mechanical inspection of all sections, bus joints, and devices
−- Bolted connection torque verification using a calibrated torque wrench, sampling per NETA ATS
−- Insulation resistance testing (phase-to-phase and phase-to-ground), minimum one minute, recorded at 30 seconds and 60 seconds
−- Contact resistance measurement on all main bus connections and feeder lug terminations
−- Circuit breaker operational testing (mechanical and electrical, all positions for drawout devices)
−- Primary current injection testing of all main and feeder trip functions (long-time, short-time, instantaneous, and ground fault pickup and time delay) at minimum one set point per function
−- Current transformer ratio and polarity verification
−- Metering accuracy verification against a calibrated reference
−- Ground impedance measurement of the equipment ground per IEEE 81
−- Functional testing of all control circuits, interlocks, and alarms
−- SPD verification of status indication and disconnect operation, where applicable
+### Insulation resistance shall be measured for one minute at 1000 V DC on a system rated above 250 V and at 500 V DC on a system rated 250 V and below, and a reading below the minimum ANSI/NETA ATS states for the voltage class shall be investigated before the switchboard is energized.
−### The scope of field testing and startup services shall be as indicated in the datasheet.
+### A switchboard that fails a field acceptance test shall not be energized, the Contractor shall report the failure to the Engineer of Record within one working day with the measured values, and the cost of the correction and of every repeated test shall be borne by the Contractor.
+### Manufacturer start-up services shall be as indicated in the datasheet.
+
```datasheet
−label: Field Testing Requirements
+label: Manufacturer Start-Up Services
type: radio
options:
− - "NETA acceptance testing and manufacturer startup"
− - "NETA acceptance testing without manufacturer startup"
− - "Manufacturer startup without independent NETA testing"
−default: "NETA acceptance testing and manufacturer startup"
+ - "Not required"
+ - "Manufacturer's field service engineer present for energization and trip unit commissioning"
```
−### Field acceptance testing shall occur after installation is complete and before the equipment is energized.
+### A manufacturer's engineer at energization sets and verifies the trip units, the ground-fault scheme, the interlocks, and the network with the maker's tools and documentation, and the visit is what the manufacturer's warranty terms often require on a switchboard with electronic trip units or a transfer scheme; a switchboard with thermal-magnetic devices and no network has little for that engineer to do. {note}
−## Infrared Thermographic Inspection {toc}
+### Infrared thermographic inspection shall be as indicated in the datasheet.
−### The infrared thermographic inspection schedule shall be as indicated in the datasheet.
−
```datasheet
label: Infrared Thermographic Inspection
−type: radio
+type: select
options:
− - "Initial scan within 90 days of energization, follow-up at 11 months"
− - "Initial scan within 90 days of energization"
- "Not required"
−default: "Initial scan within 90 days of energization, follow-up at 11 months"
+ - "One inspection within 90 days of energization"
+ - "One inspection within 90 days of energization and a second at eleven months"
```
−### Where an infrared scan is indicated in the datasheet, it shall be performed under normal operating load conditions (minimum 40% of rated load where practical).
+### Where infrared inspection is indicated, it shall be performed with the switchboard carrying not less than 40% of its rated load on each scanned connection, and every connection showing a rise of more than 10 °C above its neighbors shall be reported and corrected.
−### All connections exceeding 10°C rise above ambient shall be reported and corrected.
+### A second inspection near the end of the first year finds the termination that loosened through the first full cycle of seasonal load, which the first inspection cannot see; it costs a second visit under load and a warranty claim filed before the warranty ends. {note}
−### The 11-month follow-up scan captures connections that may loosen during the initial thermal cycling period and falls within the standard one-year warranty window. {note}
−
# Installation {toc}
−## Concrete Housekeeping Pad {toc}
+## Location and Working Space {toc}
−### See [[sync/concrete-pads]] for construction requirements. {note}
+### The room in which the switchboard is installed shall satisfy [[sync/electrical-rooms]] where that room is an electrical room.
−### Switchboard shall be mounted on a reinforced concrete housekeeping pad extending a minimum of 3 in. beyond the base of the equipment on all sides.
+### Working space in front of the switchboard, and behind it where it is rear-accessible, shall comply with NFPA 70 110.26 for the system voltage and the condition of the space, and no door swing shall reduce that space.
−### Pad shall be a minimum of 4 in. above finished floor for indoor installations and 6 in. above finished grade for outdoor installations.
+### Where the switchboard is rated 800 A or more and is over 6 ft wide, the working space shall have an entrance at each end in accordance with NFPA 70 110.26(C)(2), unless the arrangement satisfies one of the exceptions that section permits, and the doors of a room containing the switchboard shall open in the direction of egress and be equipped with listed panic hardware where that section requires it.
−### Coordinate pad dimensions, conduit penetrations, and anchor bolt locations with equipment shop drawings prior to concrete placement.
+### The dedicated electrical space above the switchboard required by NFPA 70 110.26(E) shall be kept clear of piping, ductwork, and equipment not associated with the electrical installation.
−## Equipment Setting {toc}
+### Working space shall not be used for storage at any time.
−### Contractor shall comply with the manufacturer's installation instructions, NEMA PB 2.1, and applicable rigging requirements.
+### The switchboard shall be set on a concrete housekeeping pad constructed under [[sync/concrete-pads]], extending not less than 3 in. beyond the structure on every side and not less than 4 in. above the finished floor indoors or 6 in. above finished grade outdoors, with the conduit stub-ups and the anchor locations coordinated with the reviewed shop drawings before the pad is placed.
−### After section assembly and before energizing, the Contractor shall verify the following:
+### The switchboard shall be anchored to the pad as indicated on [[drawing: the seismic anchorage details]], and where seismic certification is required the anchorage shall be that on which the certification depends, with no substitute anchor used without the manufacturer's written confirmation that the certification remains valid.
−- All shipping restraints and temporary grounds removed
−- Bus splice joints torqued per the manufacturer's specifications using a calibrated torque wrench, with witness marks applied
−- Device line and load lugs torqued per the manufacturer's published values
−- Conduit terminations sealed and cable connections trained, supported, and torqued
−- Space heaters energized for outdoor or unconditioned installations
−- Working clearances per NFPA 70 Article 110.26 maintained
−- Equipment ground bus bonded to the building grounding electrode system per [[sync/grounding-and-bonding]]
+## Setting and Assembly {toc}
−### Sections shall not be lifted by bus, doors, or device handles.
+### The Contractor shall handle, set, and assemble the switchboard in accordance with NEMA PB 2.1 and the manufacturer's instructions, lifting each shipping section by the lifting provisions furnished and never by the bus, the doors, or the device handles.
−### Remove all temporary shipping braces, blocking, and desiccants prior to final assembly.
+### Shipping sections shall be set plumb and level, aligned flush at the front, bolted together, and the bus spliced at every shipping split with the splice plates furnished, torqued to the manufacturer's values with a calibrated torque tool and witness-marked.
−## Working Clearance {toc}
+### Every shipping brace, blocking, desiccant, and temporary ground shall be removed before the switchboard is energized, and the manufacturer's shipping checklist shall be completed and included in the field test report.
−### Minimum working space shall be maintained per NFPA 70 Article 110.26 based on the nominal voltage and accessibility configuration:
+### Where the switchboard is installed in an unconditioned space or outdoors, its space heaters shall be energized from a temporary source from the day the switchboard is set until its permanent heater circuit is in service.
−| Voltage | Condition 1 (exposed on one side) | Condition 2 (exposed on both sides) | Condition 3 (exposed on both sides + operator between) |
−|---------|-----------------------------------|--------------------------------------|---------------------------------------------------------|
−| 0-150V | 36 in. | 36 in. | 36 in. |
−| 151-600V | 36 in. | 42 in. | 48 in. |
+## Conductor Terminations {toc}
−### Working space shall not be used for storage.
+### The main and feeder lugs shall be of the type indicated in the datasheet.
−### Dedicated electrical space above and below the equipment shall be maintained per NFPA 70 Article 110.26(E).
+```datasheet
+label: Main and Feeder Lug Type
+type: radio
+options:
+ - "Mechanical set-screw lugs"
+ - "Compression lugs"
+default: manufacturer
+```
−### Where the switchboard is service entrance equipment over 1200A and over 6 ft wide, a second egress path from the working space is required per NFPA 70 Article 110.26(C)(2).
+### The manufacturer shall state the lug type furnished in the product data.
−## Identification of Source {toc}
+### Mechanical lugs accept a range of conductor sizes and are the lugs the switchboard ships with; compression lugs are crimped to one conductor size with a tool matched to the lug, hold their pressure without re-torquing, and are used where the Owner's practice or the conductor material calls for them. {note}
−### Where the switchboard is fed from a remote source, a permanent label per NFPA 70 Article 408.4(B) shall identify the source location and circuit designation.
+### Every lug shall be listed for the conductor material and size terminated in it, shall be rated for 75 °C conductors, shall accept the number of conductors per phase indicated on the one-line diagram, and where aluminum conductors are terminated shall be listed for aluminum and the conductor prepared as the lug listing requires.
−### Where the switchboard supplies multiple sources (for example, normal and emergency), each source shall be clearly identified at the switchboard.
+### Every conductor termination shall be torqued to the device manufacturer's published value with a calibrated torque tool, and the values applied shall be recorded in the field test report.
+### Conductors within the switchboard shall be trained and supported so that each feeder can be identified and reached without disturbing its neighbors, shall not bear on the bus or on a device, and shall be arranged so that the conductors of each phase are grouped as the phase sequence of the bus requires.
+
+### Conductor selection and installation shall comply with [[sync/conductors-and-cables]], and raceways shall comply with [[sync/raceways-and-conduit]].
+
# Delivery, Storage, and Handling {toc}
−## Switchboard shall be shipped in the largest factory-assembled sections that can be transported to and within the installation site.
+## Each switchboard shall be shipped in the largest factory-assembled sections the delivery route and the installation pathway admit, and the Contractor shall verify the door, corridor, elevator, and turning dimensions between the delivery point and the installed location against the shipping section dimensions before the switchboard is released for manufacture.
−## Verify all pathway dimensions (doors, hallways, elevator shafts, turning radii) between the delivery point and the final installation location prior to ordering.
+## Each shipping section shall be delivered in the manufacturer's packaging with the listing marks and the nameplates intact, and shall be inspected for shipping damage at receipt.
−## Coordinate shipping splits with the manufacturer on the approved shop drawings.
+## Switchboards shall be stored indoors in a clean, dry space where the temperature is held above the dew point, and where indoor storage is not available they shall be stored under cover on pallets, off the ground, and protected from condensation, precipitation, dust, and physical damage.
−## Equipment shall be stored indoors in a clean, dry location.
+## Where a switchboard will stand more than 30 days in an unconditioned space before energization, its space heaters, where furnished, shall be energized from a temporary source, or the structure shall otherwise be protected from condensation.
−## Where indoor storage is not available, the manufacturer shall provide weatherproof packaging.
+## The structure shall remain in its packaging or covered until the conductors are pulled, so that construction dust does not settle on the bus and the device terminals.
−## Condensation heaters shall be connected and energized during storage if the equipment will be stored for more than 30 days or if the storage environment is not climate-controlled.
+## A switchboard damaged or wetted in transit, in storage, or in handling shall be repaired or replaced as the manufacturer directs and as the Engineer of Record accepts in writing.
# Warranty {toc}
−## The manufacturer shall warrant the switchboard for the period indicated in the datasheet.
+## The manufacturer shall warrant each switchboard, its bus, and every factory-installed device against defects in materials and workmanship for the period indicated in the datasheet.
```datasheet
−label: Warranty Period
+label: Manufacturer's Warranty Period
+type: range
+unit: years
+options:
+ min: 1
+ max: 5
+ setpoints: [1, 2, 3, 5]
+```
+
+## Where a warranty period is not selected in the datasheet, the manufacturer's standard warranty shall apply, and its term shall be stated in the product data.
+
+## The warranty period shall commence on the date indicated in the datasheet.
+
+```datasheet
+label: Warranty Commencement
type: select
options:
− - "1 year from substantial completion"
− - "2 years from substantial completion"
− - "3 years from substantial completion"
− - "5 years from substantial completion"
−default: "1 year from substantial completion"
+ - "Date of substantial completion"
+ - "Date of energization"
+ - "Date of shipment"
```
+## Warranty commencement at shipment is the manufacturer's usual term, and it consumes the warranty during storage and construction; commencement at energization or substantial completion moves the coverage to the period the Owner is operating the equipment, and the manufacturer prices the added months into the switchboard. {note}
+
## The warranty coverage scope shall be as indicated in the datasheet.
…4 unchanged lines
- "Parts only"
- "Parts and labor"
−default: "Parts only"
```
−## Additional warranty services shall be provided as indicated in the datasheet.
+## The Contractor shall warrant the installation, including every termination, the bus splices, the anchorage, and the field-installed accessories, for the project warranty period.
−```datasheet
−label: Additional Warranty Services
−type: checkbox
−options:
− - "Emergency response (24/7 with 4-hour commitment)"
− - "Scheduled preventive maintenance (annual)"
−```
+## A device or bus component replaced under warranty shall be warranted for the remainder of the original period or for one year from the date of replacement, whichever ends later, and the replacement shall not reduce the coverage of any other component in the switchboard.
−## Warranty shall cover defects in materials and workmanship under normal use and service conditions.
−
−## The manufacturer shall maintain a service organization capable of providing emergency replacement parts and field service within 24 hours during the warranty period.
−
# Spare Parts {toc}
−## Spare breakers shall be furnished as indicated in the datasheet.
+## The Contractor shall deliver the spare parts indicated in the datasheet to the Owner before the switchboards are accepted, and shall obtain a signed receipt for them.
```datasheet
−label: Spare Breakers
−type: radio
+label: Spare Parts to Be Furnished
+type: checkbox
options:
− - "None"
− - "One spare of each feeder frame size"
− - "10% of each frame size (minimum one)"
−default: "One spare of each feeder frame size"
+ - "One spare feeder circuit breaker of each frame size and trip unit type installed"
+ - "One set of fuses of each class and rating installed, plus one set of control fuses"
+ - "One set of blank covers for every space position on the project"
+ - "One set of indicating lamps of each type installed"
+ - "Two sets of keys for every lock and key interlock"
+ - "One pint of touch-up paint matching the finish"
+default:
+ - "One set of blank covers for every space position on the project"
+ - "Two sets of keys for every lock and key interlock"
```
−## Manufacturer shall provide the following additional spare parts:
+## Spare devices shall be identical to and interchangeable with the installed devices, shall be delivered in their original packaging, and shall be labeled with the switchboard designation and the device rating they serve.
−- One set of replacement indicating lights for each type installed
−- One set of replacement control fuses for each type and rating installed
−- One complete set of keys for all locks and Kirk key interlocks
−- Touch-up paint matching the finish color (minimum one pint)
−
−## Spare breakers shall be of the same type, rating, and configuration as the installed breakers and shall be fully interchangeable.
−
−## Spare breakers shall be stored in a manufacturer-provided storage cabinet located in the electrical room.
+## Spare devices and fuses shall be stored in a labeled cabinet in the electrical room furnished by the Contractor, and shall not be stored inside an operating switchboard.