Panelboards: What the National Electrical Code Says

panelboard Electrical Code

The National Electric code (NEC) is the standard operating procedure manual in the United Sates for the safe installation of electrical wiring and equipment. While it is not a United States law, the NEC is commonly referred to and mandated by state and local law. Therefore, the NEC sets up the minimum compliance standards for all types of electrical components, including electrical panelboards.

Article 408: Chapter III: 408.30 – panelboards

According the NEC, all panelboards must have a rating that should not be less than the minimum feeder capacity required for the loaded calculated in sections II, III, IV, or V of Article 220 as applicable.

Article 408.36: Overcurrent Protection of Panelboards

The NEC says that in addition to the requirement of article 408.36, an overcurrent protective device having a rating not greater than that of the panelboard itself should protect a panelboard. This overcurrent protective device should be located within or at any point on the supply side of the panelboard.

Exceptions to Article 408.36 Regarding Panelboards and Overcurrent Protection

  • Exception #1 regarding overcurrent protection and panelboards: Individual protection should not be required for a panelboard used as service equipment with multiple disconnecting means in accordance with article 230.71. Furthermore, in panelboards protected by three or more main circuit breakers or sets of fuses, the Circuit Breakers or sets of fuses should not supply a second bus structure within the same panelboard assembly.
  • Exception #2 regarding overcurrent protection and panelboards: Individual protection should not be required for a panelboard protected on is supply side by two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard. A panelboard constructed or wired under this exception should not contain more than 42 overcurrent devices. For the purposes of determining the maximum of 42 overcurrent devices, a 2-pole or a 3-pole circuit breaker should be considered as two or three overcurrent devices, respectively.
  • Exception #3 regarding overcurrent protection and panelboards: For existing panelboards, individual protection should not be required for a panelboard used as service equipment for an individual residential occupancy.

Article 408.40: Grounding of Panelboards

panelboard cabinets and panelboard frames, if constructed of metal, should be in physical contact with each other and should be connected to an equipment grounding conductor. When the panelboard is used with nonmetallic raceway or cable or where separate equipment grounding conductors are provided, a terminal bar for the equipment grounding conductors should be secured inside the cabinet. In addition, the terminal bar should be bonded to the cabinet and panelboard frame, if constructed of metal; otherwise it should be connected to the equipment grounding conductor that is run with the conductors feeding the panelboard.

Exception to Article 408.40: Grounding of Panelboards

When an isolated equipment grounding conductor is provided as permitted by article 250.146 (D), the insulated equipment grounding conductor that is run with the circuit conductors should be permitted to pass through the panelboard without being connected to its equipment terminal bar.