Distribution board
Normally, a main switch, and in recent boards, one or more residual-current devices (RCDs) or residual current breakers with overcurrent protection (RCBOs) are also incorporated.
[1] North American distribution boards are generally housed in sheet metal enclosures, with the circuit breakers positioned in two columns operable from the front.
Residential and light commercial panels are generally referred to as load centers and employ plug-in breakers.
The branch circuit bonding conductors are secured to a terminal block attached directly to the panelboard enclosure, which is itself grounded.
During servicing of the distribution board, when the cover has been removed and the cables are visible, American panelboards commonly have some live parts exposed.
[citation needed] The photograph to the right shows the interior of a residential service panelboard manufactured by General Electric.
Three wires (hot black, neutral white, and bare ground) can be seen exiting the left side of the enclosure running directly to a NEMA 5-15 electrical receptacle with a power cord plugged into it.
Larger commercial, public, and industrial installations generally use three-phase supplies, with distribution boards which have twin vertical rows of breakers.
In split-phase panels, separate busbars are fed directly from the incomer, which allows RCDs to be used to protect groups of circuits.
Other devices, such as transformers (e.g. for bell circuits) and contactors (relays; e.g. for large motor or heating loads) may also be used.
New British distribution boards generally have the live parts enclosed to IP2X, even when the cover has been removed for servicing.
In the United Kingdom, BS 7671 defines a consumer unit as "A particular type of distribution board comprising a type tested coordinated assembly for the control and distribution of electrical energy, principally in domestic premises..."[5] These installations usually have single-phase supplies at 230 V (nominal standard); historically, they were known as fuse boxes, as older consumer units used fuses until the advent of mini-circuit breakers (MCBs).
In the UK, consumer units (CU) have evolved from basic main switch and rewireable fuses, that afforded only overload and short circuit protection, into sophisticated control units housing many safety features that can protect against different types of electrical fault.
BS7671:2018 Requirements for Electrical Installations, also referred to as the IET Wiring Regulations, gets regularly updated and its latest edition at the time of writing is amendment 2:2022 released on 28 March 2022.
Typical configurations of CU: Modern consumer units are now required to be metal (non-combustible) and usually use DIN rail mounted devices.
The choice of consumer unit will reflect several factors such as the size and layout of the dwelling, number of floors, outbuildings, the expected loads (lighting, sockets, ovens, showers, immersion heaters, car-chargers etc.
This type of consumer unit was very popular in Britain until 2001 when wiring regulations mandated residual-current device (RCD) protection for sockets that could "reasonably be expected to" supply outdoor equipment (BS 7671:2001, ISBN 0-86341-373-0).
[7] Since the introduction of (BS 7671:2008 incorporating amendment no 1: 2011) 17th Edition IET Wiring Regulations, consumer units in the UK must provide RCD protection to all cables embedded in walls excepting high integrity circuits such as those for burglar alarms or smoke alarms.
Some older systems such as those that use MK or old MEM Consumer Units that had one fuse per spur, so for instance: etc.. A small number of pre-1950 fuseboxes are still in service.
For reasons of aesthetics and security, domestic circuit breaker panels and consumer units are normally located 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 accessible.
