National Electrical Code (NEC) Requirements for Panelboards

Electrical Technology

NEC Requirements for Electric Main Panelboards and Working Space Depth and Mounting Height

Panelboards shall be installed in accordance with the listing of the panelboard. The National Electrical Code (NEC) provides comprehensive safety standards for electrical installations, including requirements for electrical panels (main service panels and subpanels or breaker box). Here are some key NEC – 2023 codes and requirements related to electrical panels:

Related Post: IEC and BS 7671 Requirements for Consumer Unit and Distribution Board

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Panel Location, Working Space and Accessibility

The working space depth for panelboards up to 600V are mentioned in NEC 110.26 (A to D).

Clearance: Electrical panels must be installed in a readily accessible area with a minimum clearance of 30 inches (762 mm) wide, 3 ft (36 inches or 914 mm) deep, and 6.5 feet (≈ 2 meter) high in front of the panel. The panelboard’s door (hinged cover) shall be able to be opened to a full 90°.
Dedicated Space: Dedicated electrical space is required for panel from the floor to a height of 1.8 m (6 ft).
Mounting Height: Mounting height of panelboards should not higher than 6 ft 7in. (2 meters) above the floor. NEC 404.8.
Wireway Depth: The maximum permitted distance for the through (wireway) beyond the front of panelboard is 6 inches, the trough’s depth is 12 inches and switchboard’s depth is 24 inches.
Equipment in front of Panel: Any device or equipment (except meters installed in meter socket), such as a transformer, should not extend more than 6 inches beyond the front of a panelboard. This was permitted prior to 1996 but is now against the NEC 2023 codes.
Obstructions: The panelboard’s working space must be kept clear and not used for storage. No obstructions like pipes, cabinets, or doors can block access to the panel.
Location Restrictions: Electrical panels (main and subpanel) cannot be installed in bathrooms or closets (240.24 – E and D), inside cabinets, above shelving, or or close to sump pump holes. Proper lighting and illumination should be provided to the working space of service equipment and panelboards.
Firm Installation: Panelboards must be firmly secured to mounted surface and as close to the service-entrance cable.

Good to Know:

If the height of the electrical equipment is less than 6.5 feet, but when mounted, the top of the equipment exceeds 6.5 feet, the minimum workspace height shall be equal to the height of the equipment.

Example:

A panelboard with a height of 5 feet, 6 inches is mounted 18 inches above the floor. This brings the total height of the top of the panelboard to 7 feet (84 inches) from the floor. In this case, the highest position for a circuit breaker to be installed must not exceed 6 feet, 7 inches (2 meters) above the floor, as per NEC 404.8(A).

When the top of a disconnect (safety) switch is mounted at 6 feet (72 inches or 1.8 meters) above the floor, and the top of the panelboard exceeds 6.5 feet, the minimum workspace height required for the panelboard is the height of the panelboard itself. Similarly, for the disconnect switch, the required workspace height is 6.5 feet.

Panel Grounding and Bonding

According to NEC 250;

Electrical panels must be properly grounded and bonded to ensure safety and prevent electrical shocks.
The neutral and ground must be separated at sub-panels but bonded using jumper wire at the main service panel.
Grounding electrodes (e.g., ground rods) must be used, and a grounding conductor must connect the panel to them.
A panelboard must have a terminal bar for attaching the equipment grounding conductors in case nonmetallic-sheathed cable is used. (NEC 408.20)

Panel Rating and Circuit Breakers

According to NEC 408;

The electrical panel must have a sufficient ampere rating to handle the total load of the electrical system. Refer to sizing a panelboards and load centers and sizing the right capacity of a subpanel.
Circuit breakers must be rated correctly for the circuits they protect. Refer to sizing a circuit breaker.
Overcurrent protection (circuit breakers) must be sized according to the load and the conductor’s ampacity. Refer to determine the number of breakers in a main panel.
A panelboard used as service equipment does not require over-current protection on the line side if it has multiple over-current devices (NEC 408.36).
200-amp panel with 40 breaker spaces provides enough power to a house up to 3,500 sq. ft.
The minimum size of main service is 100A, 120V, 3-wires (Hot as black or red, Neutral as White and Ground as green/yellow or bare conductor) for a one-family residence. NEC 230.79(C).
Proper wiring color codes should be used according to the NEC and IEC wiring color codes for AC and DC.

Panel Labeling

According to NEC 408.4,

Each circuit in the panel must be clearly and accurately labeled. NEC 408.4 and 2021 IRC – Section E3706.2.
The labeling must identify the equipment or area served by each circuit.
Unused opening for circuit breakers and switches shall be closed using identified closures. (NEC 408.7).
Disconnect and panelboard used as service equipment must be marked as “Suitable for Use as Service Equipment” NEC 230.66.

Neutral Bar and Ground Bar Separation

According to NEC 250.24;

In sub-panels, the neutral and ground bars must be separated to prevent ground faults.
In the main panel, the neutral and ground must be bonded by Main Bonding Jumper (MBJ) wire from manufacturer as crossover tie bar, but in sub-panels, they must be isolated.
Never connect the equipment grounding conductor to the neutral bar if the panelboard is not lactated as the service equipment.
For grounded branch-circuit conductors, one conductor per terminal is allowed according NEC 408.41
The connection of neutral conductor for service and branch circuits and equipment grounding conductors at panelboards must comply in accordance with NEC 408.40 and 408.41.

GFCI and AFCI Protection

According to NEC 210.12 and 210.8; Arc Fault Circuit Interrupters (AFCI) and Ground Fault Circuit Interrupters (GFCI) and surge protectors etc. must be used in the main panel to protect both the device and operator e.g.:

AFCI protection is required for most residential circuits (e.g., bedrooms, living rooms).
GFCI protection is required for outlets in areas like kitchens, bathrooms, and outdoor locations to prevent electrical shock.

Panel Fill Capacity

According to NEC 312.7;

The number of circuits or circuit breakers in a panel must not exceed the panel’s listed capacity.
The panel must not be overcrowded, and wire fill must comply with the panel’s design specifications.
Refer to hot to determine the number of breakers in a main panel?
A panelboard shall not exceed 80% of its full rated capacity where the remaining open slots can be used for future load and expansion.
Unused knockouts and openings in electrical equipment panelboard other than openings for mounting purposes or special equipment must be sealed to provide protection equal to the cabinet wall of the equipment.

Main Disconnect

According to NEC 230.70;

The main service panel must have a main disconnect or breaker that can disconnect all power to the building.
The disconnect must be located either in the panel or adjacent to the panel.
the main service disconnect must be permanently marked to identify it as service disconnect (NEC 230.70(B).
The service disconnect must be located on the building and easily accessible If the main disconnecting is located outside. (NEC 230.70(A)(1).
The service disconnect shall have a rating not less than the calculated load to be carried in accordance article 220. (NEC 230.79). To know the value of calculated load, refer to how to size a load center, panelboards and distribution board?
Panels that serve as the main disconnect must have no more than six switches (or disconnects) to shut off all power while at one location.
For additional guidelines and requirements regarding service disconnects, refer to NEC sections 230.70 through 230.82.

Service Entrance Conductors

According to NEC 230.71;

Service entrance conductors (wires that bring electricity from the utility) must be appropriately sized and installed to meet load demands and NEC requirements. Refer to how to find the right wire size and how to find the right wire size for 100A service – 120V/240V Panel?
Proper Service-entrance cables either copper, aluminum or copper-clad aluminum should be used i.e. Type SE (U and R), SER, SEU, USE (and USE-2), TC (Tray Cable), THWN/THHN, and XHHW etc. in accordance with NEC 240.21(B and C) 310, 230 and 338.
Sizing of wires and cables must comply the Table 310.15(B) (16), 230.42 for services, 215.2(A)(1) for feeders, 310.15(B)(7) for 120/240-volt, 3-wire 1-phase dwelling services and feeders, 338.10(B) for branch circuits and feeders, interior and exterior installations.

Weatherproof Panels for Outdoor Installations

According to NEC 312.2;

Panels installed outdoors must be weatherproof and designed to handle environmental exposure.
Panels must have a proper enclosure with weatherproof covers.
Panels installed within a wall for flush mounting i.e. plaster, drywall, or plasterboard, repair wall so
opening or gap is greater than 3mm (1/8 inches) NEC 312.3 and 312.4.
In case of dump or wet locations, there be at least a 6 mm (1⁄4 inches) air space between the wall and a surface mounted enclosure to account the moisture and prevent the rusting and damaging of equipment inside the enclosure (NEC 312.2).
In case of noncombustible material such as tiles, wall of concrete, set back not more than 6 mm (1⁄4 inches).

By following NEC standards, electrical panels are designed to operate safely and prevent electrical hazards in both residential and commercial installations.