The National Electrical Code (NEC) defines a panelboard as a single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front.
MAIN BREAKER PANELBOARD: has a main disconnect installed between the lugs where the service entrance cables connect and the supply bus bars.
MAIN LUG PANELBOARD: has no main disconnect installed. Power to the panel is controlled from a main disconnect at another location, typically the electrical service.
CABINET DEFINITION: A cabinet is an enclosure designed for interior installation that may be either surface or flush mounted and has a frame or trim to which swinging doors are attached.
CUTOUT BOX DEFINITION: A cutout box is designed for surface mounting. It may be installed inside out outside and has a door hinged at the top or side.
- LIGHTING AND BRANCH CIRCUIT PANELBOARDS (NEC)
A lighting and appliance branch- circuit panelboard must have more than 10% of its overcurrent protective devices (OCPD) protecting lighting and appliance branch circuits.
A lighting and appliance branch circuit is a branch circuit that has a connection to the neutral of the panelboard and has overcurrent protection of 30 amperes or less in one or more conductors.
A lighting and appliance branch- circuit panelboard is limited to no more than 42 OCPD (poles) in any one cabinet or cutout box.
- POWER (DISTRIBUTION) PANELBOARDS
A power panelboard is one that has 10% or fewer of its OCPDs protecting lighting and appliance branch- circuits.
A panelboard has 42 OCPDs but only four OCPD are rated at 30 amps or less. Since four is less than 10% of 42, this panelboard doesn't qualify as a lighting and appliance branch- circuit panelboard.