Simplifying the NEC definition, panelboards are: accessible only from the front, mounted against or in a wall, placed in a cabinet or cutout box, and used to control light, heat, or power circuits.
Panelboard Applications and Types
Panelboards are designed for a multitude of applications. For example, they are manufactured for various voltages (120/240vac, 120/208vac, and 277/480vac being the most common in the U.S.), amperages (ranging from 30A to 400A), and phases (single 1Ø or three phase 3Ø). Panelboards basically fall into three categories:
- Lighting and appliance branch-circuit panelboards
- Power panelboards
- Load centers
The cabinet enclosure, or cutout box and its front cover (usually a hinged door) are designed for specific installations following guidelines set forth by the National Electrical Manufacturers Association (NEMA). Common enclosure types include (for a complete listing of enclusure types click here):
- Type 1 enclosures are intended for general purpose indoor use.
- Type 3R enclosures are intended for outdoor use, primarily to provide a degree of protection against rain, sleet, and damage from external ice formation.
- Type 4X enclosures are intended for indoor or outdoor use, primarily to provide a degree of protection against corrosion, windblown dust and rain, splashing water, hose-directed water, and damage from external ice formation.
- Type 3R/12 enclosures are intended for indoor use, primarily to provide a degree of protection against circulating dust, falling dirt, and dripping noncorrosive liquids.
The interior of a panelboard consists of several components, including overcurrent protection devices (usually circuit breakers), main lugs or a main circuit breaker, bus bars (a bus bar is a conductor that serves as a common connection for two or more circuits -- breakers are attached to the bus bars), insulated neutral bus bars, and ground bus bars (when required).
