1 Scope
NOTE This standard covers dead-front panelboards rated 1000 V or less for use in commercial, institutional, and light-to-medium industrial buildings. (1.1)
NOTE It applies to lighting-and-appliance panelboards and power distribution panelboards installed as sub-distribution points fed from switchboards, switchgear, or larger panelboards. (1.2)
NOTE The scope includes main-breaker and main-lug-only configurations, surface- and flush-mounted enclosures, and the branch-circuit overcurrent devices housed within the panelboard. (1.3)
NOTE A panelboard is a single-panel or group-of-panels assembly designed for installation in a cabinet or cutout box, accessible only from the front, and includes buses and overcurrent devices for the control of light, heat, or power circuits. The dead-front construction places no energized parts on the operating face once the trim is installed. (1.4)
NOTE The following are excluded from this standard. (1.5)
NOTE Residential-grade low-voltage load centers (typically 200 A or less, tested to the consumer-product provisions of UL 67) are covered by
Low Voltage Panelboards.
(1.5.1) NOTE Grounding electrode conductors, bonding jumpers, and equipment grounding terminations within the panelboard are covered by
Grounding And Bonding.
(1.5.3) NOTE Feeder and branch conductors entering and leaving the panelboard are covered by
Conductors And Cables.
(1.5.4) NOTE Switchboards, switchgear, and multi-section distribution lineups (typically mains above 1600 A) are outside the scope of UL 67 and NEMA PB 1 and are specified under a separate switchboard standard. (1.5.5)
NOTE Medium-voltage distribution panels rated above 1000 V are outside the scope of UL 67 entirely. (1.5.6)
2 Referenced Standards
2.1Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
NOTE The adoption of the National Electrical Code and its effective edition varies by jurisdiction; the edition enforced by the Authority Having Jurisdiction shall be verified before fabrication. (2.3)
| Standard |
Title |
| UL 67 |
Panelboards |
| NEMA PB 1 |
Panelboards |
| ANSI/NEMA PB 1.1 |
General Instructions for Proper Installation, Operation and Maintenance of Panelboards Rated 1000 V or Less |
| NFPA 70 (NEC), Article 408 |
National Electrical Code - Switchboards, Switchgear, and Panelboards |
| NFPA 70 (NEC), Article 240 |
National Electrical Code - Overcurrent Protection |
| NFPA 70 (NEC), Article 230 |
National Electrical Code - Services |
| NFPA 70 (NEC), Article 285 |
National Electrical Code - Surge-Protective Devices |
| NFPA 70 (NEC), Article 220 |
National Electrical Code - Branch-Circuit, Feeder, and Service Load Calculations |
| NFPA 70 (NEC), Article 110 |
National Electrical Code - Requirements for Electrical Installations |
| NFPA 70 (NEC), Article 700 |
National Electrical Code - Emergency Systems |
| IEEE 1584 |
Guide for Performing Arc-Flash Hazard Calculations |
| UL 489 |
Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures |
3 Submittals
3.1 Action Submittals
3.1.1The Contractor shall submit the following action submittals for review and approval before fabrication:
- Product data for each panelboard type, including ratings, dimensions, enclosure type, and bus material.
- Shop drawings showing panelboard schedule, circuit arrangement, ampere ratings, and interrupting ratings.
- Panelboard schedules listing each branch circuit, its overcurrent device rating, number of poles, and connected load.
- Dimensioned enclosure drawings showing gutter space, wiring space, and conduit entry locations.
- Short-circuit current rating (SCCR) of each panelboard with supporting documentation.
- Wiring diagrams differentiating factory-installed and field-installed wiring.
☐ Product data
☐ Shop drawings
☐ Panelboard schedules
☐ Enclosure dimension drawings
☐ SCCR documentation
☐ Wiring diagrams
3.1.2Where selective coordination is required for an emergency, legally required standby, or critical operations power system, the Contractor shall submit a coordination study sealed by a registered professional engineer.
3.1.3Where an arc-flash study is required by the Owner or the Authority Having Jurisdiction, the Contractor shall submit incident-energy calculations performed in accordance with IEEE 1584.
3.2.1The Contractor shall submit the following informational submittals:
- Manufacturer's product certifications confirming UL 67 listing.
- Field quality-control test reports, including torque verification records.
- Source quality-control reports for factory-installed surge protective devices.
☐ UL 67 listing certification
☐ Field test reports
☐ Torque verification records
☐ SPD source test reports
3.3 Closeout Submittals
3.3.1The Contractor shall submit the following closeout submittals before final acceptance:
- Operation and maintenance manuals prepared in accordance with ANSI/NEMA PB 1.1.
- As-built panelboard schedules reflecting final installed circuit assignments.
- Final laminated or typed circuit directory installed in each panelboard.
- Warranty documentation.
☐ Operation and maintenance manuals
☐ As-built panelboard schedules
☐ Final circuit directory
☐ Warranty documentation
4 Quality Assurance
4.1Each panelboard shall be listed and labeled to UL 67 by a Nationally Recognized Testing Laboratory.
4.2Each branch-circuit and main overcurrent device shall be listed to UL 489 where it is a molded-case circuit breaker.
NOTE Panelboards shall be the product of a single manufacturer for a given project to maintain interchangeability of breakers and trim. (4.3)
NOTE Using a single manufacturer across a project allows spare breakers and replacement parts to be stocked once and installed in any panel, and avoids field confusion between visually similar but non-interchangeable breaker lines. (4.3.1)
4.4The manufacturer shall have produced panelboards of the type specified for a minimum of five years.
4.5Field modifications that alter the listing, such as drilling additional knockouts in a NEMA 3R enclosure or adding non-listed components, shall void the listing and are prohibited.
5 Ratings
5.1 Panelboard Class
NOTE A lighting-and-appliance panelboard is one having more than 10 percent of its overcurrent devices rated 30 A or less for which neutral connections are provided; a power distribution panelboard is any panelboard that is not a lighting-and-appliance panelboard. (5.1.1)
NOTE The classification governs the maximum overcurrent device count and main-device rules under NEC Article 408; misclassifying a panel leads to upsized or non-code-compliant designs and is a frequent code-interpretation error. (5.1.2)
5.1.3Each panelboard shall be classified as a lighting-and-appliance panelboard or a power distribution panelboard.
● Lighting-and-appliance
○ Power distribution
5.1.4A lighting-and-appliance branch-circuit panelboard shall not contain more than 42 overcurrent devices, excluding the main, in a single cabinet or cutout box.
5.2 Voltage and Phase
NOTE The system voltage, phase, and number of wires for each panelboard are determined by the upstream distribution design and shown on the drawings. (5.2.1)
5.2.2Each panelboard shall be rated for the system voltage and phase configuration indicated.
○ 120/240 V 1Φ 3-wire
● 120/208 V 3Φ 4-wire
○ 277/480 V 3Φ 4-wire
5.2.3The panelboard voltage rating shall equal or exceed the nominal system voltage at the point of installation.
5.3 Main Device
NOTE A main-breaker (MCB) panelboard includes an integral overcurrent device on the line side of the branch buses; a main-lug-only (MLO) panelboard terminates the feeder directly on the bus with no integral main device. (5.3.1)
NOTE A main lug only panelboard relies on an upstream overcurrent device for its main protection; specifying MLO where NEC 225.32 or 230.70 requires a disconnecting means at the panel results in field relabeling or replacement. (5.3.2)
5.3.3Each panelboard shall be furnished as a main-breaker or main-lug-only type as indicated.
● Main circuit breaker (MCB)
○ Main lug only (MLO)
5.3.4A lighting-and-appliance branch-circuit panelboard shall be provided with individual protection on the supply side by an overcurrent device rated not greater than the panelboard rating, unless protection is otherwise provided in accordance with NEC 408.36 exceptions.
5.3.5The main device ampere rating shall be coordinated with the calculated load per NEC Article 220 and with the rating of the bus.
100
125
150
200
225
250
400
600
800
1000
1200
Per drawings — panelboard schedule
5.4 Bus Rating
5.4.1The main bus continuous current rating shall be not less than the main device rating and not less than the calculated continuous load.
5.4.2The bus bracing shall withstand the mechanical stresses produced by the short-circuit current rating of the panelboard.
100
125
150
200
225
250
400
600
800
1000
1200
Per drawings — panelboard schedule
5.5 Short-Circuit Current Rating
NOTE The short-circuit current rating (SCCR) is the maximum prospective fault current the panelboard can safely interrupt or withstand; it must equal or exceed the available fault current at the point of installation under NEC 110.10. (5.5.1)
NOTE The available fault current depends on the upstream transformer, utility contribution, and conductor impedance, and must be stated on the drawings; specifying an SCCR without providing the available fault current forces the Contractor to submit an RFI. (5.5.2)
5.5.3The panelboard short-circuit current rating shall equal or exceed the available fault current at the line terminals.
5.5.5A series-rated combination shall be applied only where the combination is tested and listed, and the panelboard shall be field-marked to indicate the series combination rating and the devices involved.
6 Overcurrent Devices
6.1 Branch Breaker Mounting
NOTE Bolt-on breakers are secured to the bus with a threaded fastener; plug-in breakers engage the bus by a stab connection and are retained by spring tension. (6.1.1)
NOTE Some Owner standards and Authorities Having Jurisdiction require bolt-on breakers for reliability in commercial applications; specifying a panel that accepts only plug-in breakers in that case will generate substitution requests. (6.1.2)
6.1.3Branch-circuit breakers shall be of the mounting type indicated for the panelboard.
6.2 Branch Breaker Type
6.2.1Branch-circuit overcurrent devices shall be thermal-magnetic molded-case circuit breakers unless a fused branch device is indicated.
6.2.2Branch breakers serving circuits required by NEC to have arc-fault or ground-fault protection shall be of the corresponding type.
Standard thermal-magnetic
Ground-fault circuit interrupter (GFCI)
Arc-fault circuit interrupter (AFCI)
Combination AFCI/GFCI
6.2.3Tandem (twin) breakers shall be used only in panelboard positions specifically listed to accept them and only where permitted by NEC 408.54.
6.2.4Each branch breaker shall have an interrupting rating not less than the available fault current at its line terminals.
6.3 Spaces and Spares
NOTE The number of circuit spaces (poles) shall be coordinated with the distribution design; specifying a panel smaller than the required circuit count forces change orders or additional panels. (6.3.1)
6.3.2Each panelboard shall provide the number of circuit positions indicated.
Per drawings — panelboard schedule
6.3.3Each panelboard shall be furnished with the indicated number of spare overcurrent devices, installed and connected to spare bus positions.
6.3.4Each panelboard shall retain a minimum percentage of its positions as unequipped spaces for future circuits.
7 Construction
7.1 Bus Material
NOTE Copper bus has lower resistivity and is dimensionally stable at terminations; aluminum bus is lighter and lower cost but requires controlled torque and anti-oxidant compound to maintain a stable connection over time. (7.1.1)
NOTE Aluminum connections that are not properly torqued and treated loosen over time and develop high-resistance hot spots; specifying aluminum bus without stating these requirements is a recurring source of failures. (7.1.2)
7.1.3Panelboard buses shall be of the material indicated.
7.1.4Where aluminum bus or aluminum lug connections are used, terminations shall be made with the manufacturer's specified torque value and treated with a listed anti-oxidant compound.
7.1.5Bus bars shall be of uniform cross-section throughout the length of the panelboard for the full ampere rating.
7.2 Neutral and Ground Bus
7.2.1Each panelboard supplying a circuit requiring a neutral shall include a full-capacity insulated neutral bus rated for the same current as the phase bus.
7.2.2Each panelboard shall include an equipment grounding bus bonded to the enclosure.
7.2.3An isolated (insulated) equipment grounding bus shall be provided only where indicated for sensitive-equipment branch circuits.
● Standard bonded ground bus
○ Standard plus isolated ground bus
7.3 Enclosure
NOTE The enclosure NEMA type shall be selected for the environment of the installation; an indoor type installed outdoors or in a wash-down area will admit water or dust and corrode. (7.3.1)
7.3.2Each panelboard enclosure shall be rated for the indicated NEMA type.
● NEMA 1 (indoor, general purpose)
○ NEMA 3R (outdoor, rainproof)
○ NEMA 4X (corrosion-resistant, wash-down)
○ NEMA 12 (industrial, dust-tight)
7.3.3Enclosure boxes and trims shall be fabricated from sheet steel finished with a corrosion-resistant coating, or from stainless steel where a NEMA 4X corrosion-resistant rating is indicated.
7.3.4The enclosure shall provide gutter and wiring space not less than the minimum required by NEC Article 408 and UL 67 for the conductors installed.
7.4 Mounting
NOTE A surface-mounted panel is fastened to the wall face; a flush-mounted panel is recessed into the wall with only its trim exposed, and requires the wall depth and conduit stub-outs to be coordinated before rough-in. (7.4.1)
7.4.2Each panelboard shall be furnished for the indicated mounting method.
● Surface
○ Flush
○ Semi-flush
7.4.3Flush-mounted panelboards shall be furnished with empty conduit stub-outs from the gutter to an accessible location above an accessible ceiling for future circuit extension.
7.5 Trim and Door
7.5.1The front trim shall be of the dead-front type, concealing all energized parts and breaker line terminals when the door is open.
7.5.2The door shall be furnished with a flush latch and a key lock, and all panelboards on a project shall be keyed alike.
7.5.3A directory cardholder with a transparent cover shall be mounted on the inside face of the door.
8 Service-Entrance and Special Provisions
8.1 Service-Entrance Rating
NOTE Standard panelboards lack the main bonding jumper, neutral-to-ground bond, and service markings required of service equipment; a panel used as the first means of disconnect after the meter must be specified as service-entrance rated. (8.1.1)
8.1.2Where the panelboard serves as service equipment, it shall be listed and labeled as suitable for use as service equipment.
8.1.3Where the panelboard is service equipment, a factory-installed main bonding jumper connecting the neutral bus to the enclosure shall be provided.
8.2 Surge Protective Device
NOTE The NEC requires surge protective devices on service-entrance equipment for most commercial buildings, and carrying surge protection downstream to sub-panels serving sensitive equipment areas protects those loads from internally generated transients. (8.2.1)
NOTE A factory-installed surge protective device offers a lower let-through voltage and a shorter lead length than a field-installed unit, but commits the panel to a single SPD model; a field-installed unit is more flexible. (8.2.2)
8.2.3A surge protective device shall be provided where indicated, either factory-installed within the panelboard or field-installed at the panelboard.
None
Factory-installed integral SPD
Field-installed SPD
8.2.4The surge protective device, where provided, shall be a Type 1 or Type 2 device as required by its point of connection under NEC Article 285.
8.3 Selective Coordination
NOTE Selective coordination requires that only the overcurrent device nearest a fault opens, leaving upstream devices closed; the NEC mandates it for emergency, legally required standby, and critical operations power systems. (8.3.1)
NOTE Selective coordination must be demonstrated by a study comparing actual breaker time-current curves; it cannot be assumed from device ratings alone. (8.3.2)
8.3.3Where the panelboard serves an emergency, legally required standby, or critical operations power system, the overcurrent devices shall be selectively coordinated with all upstream and downstream devices.
8.4 Metering
8.4.1Where indicated, the panelboard shall include integral metering provisions, current transformers, or a meter socket within or adjacent to the enclosure.
None
Current transformer compartment
Integral revenue meter socket
Integral power/energy meter
9 Identification
9.1A permanent nameplate shall be affixed to each panelboard identifying its designation, voltage, phase, main device rating, and source.
9.2Each panelboard shall be field-marked with the maximum available fault current and the date the calculation was performed, in accordance with NEC 110.24.
9.3A series-combination-rated panelboard shall be field-marked to identify the series rating and the devices that establish it.
NOTE A typed or computer-generated circuit directory accurately identifying the load served by each circuit shall be installed in each panelboard at closeout, in accordance with NEC 408.4. (9.4)
NOTE The NEC requires permanent, legible circuit identification, yet specifications often omit the requirement for the final laminated schedule, leaving hand-written directories that become illegible. (9.4.1)
9.4.2A typed or computer-generated circuit directory shall be installed in the directory cardholder of each panelboard at closeout.
10 Environmental and Service Conditions
NOTE Panelboards shall be suitable for continuous operation at the ambient temperature of the installed location without derating below the rating indicated. (10.1)
10.1.1Each panelboard shall be rated for service at the indicated maximum ambient temperature.
10.1.2Each panelboard installed above an indicated elevation shall be derated in accordance with the manufacturer's altitude correction data.
11 Testing
11.1 Source Quality Control
11.1.1Each panelboard shall be production tested at the factory in accordance with UL 67, including a dielectric withstand test.
11.1.2Each factory-installed surge protective device shall be functionally tested at the factory before shipment.
11.2 Field Quality Control
11.2.1After installation, each panelboard shall be inspected for tightness of all bus and terminal connections.
11.2.2Each accessible bolted bus and lug connection shall be torqued to the manufacturer's published value and the value shall be recorded.
11.2.3Each branch and main overcurrent device shall be exercised manually from off to on to off before energization.
11.2.4Insulation-resistance testing shall be performed phase-to-phase and phase-to-ground before energization where required by the Owner.
☐ Connection tightness inspection
☐ Torque verification with recorded values
☐ Manual operation of all devices
☐ Insulation-resistance test
12 Installation
12.1 Working Clearances
NOTE The dedicated electrical space above a panelboard - extending from the floor to a height of 1.8 m above the equipment or to the structural ceiling, whichever is lower - must be kept clear of piping, ducts, and other systems not serving the equipment under NEC 110.26(F). (12.1.1)
NOTE Ceiling soffits, ductwork, and piping routed through the dedicated space above a panel are a frequent source of field conflicts and RFIs when not coordinated on the architectural drawings during design. (12.1.2)
12.1.3Each panelboard shall be installed with the working clearances required by NEC 110.26 maintained clear of obstruction.
12.1.4The dedicated electrical space above each panelboard shall be kept clear of foreign systems in accordance with NEC 110.26(F).
12.1.5Panelboards shall not be installed in the dedicated space of, or within the working clearance of, other equipment unless the arrangement is shown on the drawings electrical room equipment layout. 12.2 Mounting Height
12.2.1Each panelboard shall be mounted so that the highest operating handle does not exceed the maximum reach height permitted by NEC 240.24.
12.2.2Panelboards shall be mounted plumb and securely fastened to the building structure, independent of the conduit entering the enclosure.
12.3 Connections
12.3.1Feeder and branch conductors shall be terminated at the panelboard lugs with the conductor material for which the lug is listed.
12.3.2Aluminum conductor terminations shall be treated with a listed anti-oxidant compound and torqued to the manufacturer's value.
12.3.3Circuits shall be balanced across the phases so that the load on any phase does not deviate from the average phase load by more than the indicated tolerance.
13 Delivery, Storage, and Handling
13.1Panelboards shall be delivered to the site in the manufacturer's original packaging with the listing label and ratings intact.
13.2Panelboards shall be stored indoors in a clean, dry space and protected from construction dust, moisture, and physical damage until installation.
13.3Panelboards shall be kept covered and energized with space heaters where provided, or otherwise protected from condensation, during prolonged storage.
14 Warranty
14.1The manufacturer shall warrant each panelboard and its overcurrent devices against defects in materials and workmanship for the indicated period from the date of substantial completion.
14.2The warranty shall cover repair or replacement of defective components, including labor for replacement of factory-installed devices.
15 Spare Parts
15.1The Contractor shall furnish spare branch-circuit breakers of each frame and pole configuration used, in the indicated quantity, delivered to the Owner at closeout.
15.2The Contractor shall furnish spare directory cards and blank trim fillers for each panelboard type.