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A distribution board (also known as panelboard or breaker panel) is a component of an electricity supply system which divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit in a common enclosure. Normally, a main switch, and in recent boards, one or more residual-current devices (RCD) or residual current breakers with overcurrent protection (RCBO), are also incorporated.
Distribution boards are also referred to as a:
circuit breaker panel
Consumer unit, or CU
Most of the time, the panel and the breakers inserted into it must both be from the same company. Each company has one or more "systems", or kinds of breaker panels, that only accept breakers of that type. In Europe this is still the case, despite the adoption of a standard DIN rail for mounting and a standard cut-out shape, as the positions of the busbar connections are not standardised.
Certain panels use seemingly interchangeable 1-inch-wide (25 mm) breakers. However, a given manufacturer will often specify exactly what devices are permitted to be installed in their equipment. These assemblies have been tested and approved for use by a recognized authority. Replacing or adding equipment which "just happens to fit" can result in unexpected or even dangerous conditions. Such installations should not be done without first consulting knowledgeable sources, including manufacturers.
A three phase service drop enters through the side of this main service panel consisting of three 100 ampere fuses.
For reasons of aesthetics and security, circuit breaker panels are often placed in out-of-the-way closets, attics, garages, or basements, but sometimes they are also featured as part of the aesthetic elements of a building (as an art installation, for example) or where they can be easily accessed. However, current US building codes prohibit installing a panel in a bathroom (or similar room), in closets intended for clothing, or where there is insufficient space for a worker to access it. Specific situations, such as an installation outdoors, in a hazardous environment, or in other out-of-the-ordinary locations may require specialized equipment and more stringent installation practices.
Large buildings or facilities with higher electric power demand may have multiple circuit breaker panels. Outlets may be labeled with the panel number and circuit number to allow quick identification of the source for maintenance.
Distribution boards may be designated for three-phase or single-phase and normal power or emergency power, or designated by use such as distribution panels for supplying other panels, lighting panels for lights, power panels for equipment and receptacles and special uses. Panels are located throughout the building in electric closets serving a section of the building.
In a theatre a specialty panel called a dimmer rack is used to feed stage lighting instruments. A US style dimmer rack has a 208Y/120 volt 3-phase feed. Instead of just circuit breakers, the rack has a solid state electronic dimmer with its own circuit breaker for each stage circuit. This is known as a dimmer-per-circuit arrangement. The dimmers are equally divided across the three incoming phases. In a 96 dimmer rack, there are 32 dimmers on phase A, 32 dimmers on phase B, and 32 on phase C to spread out the lighting load as equally as possible. In addition to the power feed from the supply transformer in the building, a control cable from the lighting desk carries information to the dimmers in a control protocol such as DMX-512. The information includes lighting level information for each channel, by which it controls which dimmer circuits come up and go out during the lighting changes of the show (light cues), and over what fade time.
Distribution boards may be surface-mounted on a wall or may be sunk into the wall. The former arrangement allows for easier alteration or addition to wiring at a later date, but the latter arrangement may look neater, particularly in a residential situation. The other problem with recessing a distribution board into a wall is that if the wall is solid a lot of brick or block may need to be removed - for this reason recessed boards are generally only fitted on new-build projects when the required space can be built into the wall