Editing Distribution board (section)

==United Kingdom==
[[File:UKDistributionBoard.JPG|thumb|right|One type of UK distribution board.]]
This picture shows the interior of a typical distribution panel in the United Kingdom. The three incoming phase wires connect to the busbars via a main switch in the centre of the panel.  On each side of the panel are two [[busbar]]s, for neutral and earth.  The incoming neutral connects to the lower busbar on the right side of the panel, which is in turn connected to the neutral busbar at the top left. The incoming earth wire connects to the lower busbar on the left side of the panel, which is in turn connected to the earth busbar at the top right.  The cover has been removed from the lower-right neutral bar; the neutral bar on the left side has its cover in place.

Down the left side of the phase busbars are two two-pole [[Residual-current device|RCBO]]s and two single-pole breakers, one unused. The two-pole RCBOs in the picture are not connected across two phases, but have supply-side neutral connections exiting behind the phase busbars. Down the right side of the busbars are a single-pole breaker, a two-pole RCBO and a three-pole breaker.

The illustrated panel includes a great deal of unused space; it is likely that the manufacturer produces 18- and 24-position versions of this panel using the same chassis.

Larger commercial, public, and industrial installations generally use three-phase supplies, with distribution boards which have twin vertical rows of breakers.  Larger installations will often use subsidiary distribution boards.

In both cases, modern boards handling supplies up to around 100&nbsp;A (CUs) or 200&nbsp;A (distribution boards)  use circuit breakers  and RCDs on [[DIN rail]] mountings.  The main distribution board in an installation will also normally provide a main switch (known as an ''incomer'') which switches the phase and neutral lines for the whole supply.  (n.b., an incomer may be referred to, or sold as, an ''[[Isolator switch|isolator]]'', but this is problematic, as it will not necessarily be used as an isolator in the strict sense.)

For each phase, power is fed along a [[busbar]]. In split-phase panels, separate busbars are fed directly from the incomer, which allows RCDs to be used to protect groups of circuits.  Alternatively RCBOs may be used to provide both overcurrent and residual-current protection to single circuits.

Other devices, such as [[transformer]]s (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 [[IP Code|IP2X]], even when the cover has been removed for servicing.

===Consumer units===
[[Image:FuseBoxforWikipedia.jpg|thumb|Old Wylex standard consumer unit fitted with seven wire fuses (one fuse-way is not in use)]]
[[Image:ModernConsumerUnitHager.JPG|thumb|Hager consumer unit fitted with MCBs, one RCD, and one double-pole switch]]
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..."<ref>IET Wiring Regulations Seventeenth Edition - British Standard BS7671:2008, Part 2 Definitions</ref> These installations usually have single-phase supplies at 230 V (nominal standard); historically, they were known as [[Fuse (electrical)#Fuse boxes|fuse boxes]], as older consumer units used [[Fuse (electrical)|fuses]] until the advent of [[circuit breaker|mini-circuit breakers]] (MCBs).
A normal new domestic CU used as a main panel might have from 6 to 24 ways for devices (some of which might occupy two ways), and will be split into two or more sections (e.g. a non-RCD section for alarms etc., an RCD-protected section for socket outlets, and an RCD-protected section for lighting and other built-in appliances).  Secondary CUs used for outbuildings usually have 1 to 4 ways plus an RCD.

Recent (pre-17th edition wiring regulations) CUs would not normally have RCD protected sections for anything other than socket outlets, though some older CUs featured RCD incomers. Before 1990, RCDs (and split busbars) were not standard in CUs.

<gallery caption="Old rewirable-fuse boxes" widths="100px" align="centre">
File:Mem_1957_cu_closed.jpg|1950s MEM rewirable fuse box (covered)
File:MEM_1957_cu_open.jpg|1950s MEM rewirable fuse box (open)
File:Mem_1977_cu_closed.jpg|1970s MEM rewirable fuse box (covered)
File:Mem_1977_cu_open.jpg|1970s MEM rewirable fuse box (open)
</gallery>
Fuse boxes normally use cartridge or rewirable fuses with no other protective device, and basic 4-ways boxes are very common. Some older boxes are made of brown-black bakelite, sometimes with a wooden base. Although their design is historic, these were standard equipment for new installs as recently as the 1980s, so they are very common. Fuseholders in these boxes may not provide protection from accidental contact with live terminals.

==== Examples ====
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. The choice of circuit protective device will depend upon the type of electrical circuit it is protecting and what level of protection needs to be afforded. 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:
* Main switch consumer unit - Consists of a main switch that will disconnect power to all circuits simultaneously which has one busbar linking all protective devices to a common live source, and one neutral conductor or link bar connecting to a common neutral rail. There will be a separate earth rail to allow the main earth conductor to be connected. This example offers the highest degree of circuit separation as all circuits are independent. This particular example amay not be suitable as a standalone solution with only overload and short circuit protection [[circuit breaker|MCBs]] for each circuit. Additional protection from earth leakage [[residual-current device#RCBO|RCBOs]] faults and arc faults [[AFDD]] may be required by BS7671 making this an expensive solution.
* Main Switch and Dual RCD consumer unit - Consists of a main switch that will disconnect power to all circuits simultaneously and two 30mA RCDs [[residual-current device|RCDs]] each with its own live busbar each protecting a separate bank of circuits, typically half-and-half but other combinations are available, from earth leakage faults. Offers a cost-effective solution by using a combination of cheaper mcbs and only two, more expensive, RCDs. 
* High integrity consumer unit - Consists of a main switch that will disconnect power to all circuits simultaneously and three separate live busbars, one linked directly to the main switch and two others on each main RCD. The live busbar on the main switch allows the use of mcbs only where more sensitive devices such as RCBOs and AFDDs would not be appropriate, or the independent use of RCBOs, and may be limited to only one or two ways. The remainder of the circuits are divided in the same way as a dual RCD CU. This type of consumer unit offers improved circuit separation over a dual RCD CU whilst allowing for more flexibility.
* RCD incomer consumer unit - This is the least convenient solution in terms of circuit separation because the main switch is an RCD. Less common than the other types, it is no longer considered a standalone solution because power to all circuits is lost in the event of an earth fault causing the main switch RCD to activate.

Modern consumer units are now required to be metal (non-combustible) and usually use [[DIN rail]] mounted devices. The DIN rail is standardized but the [[busbar]] arrangements are not. Mixing of different brands devices is against the manufacturers requirements and should generally be avoided.

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.), and how much protection is required for each circuit.

The box pictured top-right is a "Wylex standard" fitted with rewirable fuses. These boxes can also be fitted with cartridge fuses or miniature [[circuit breaker]]s (MCBs). This type of consumer unit was very popular in [[United Kingdom|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}}). There were a number of similar designs from other manufacturers but the Wylex ones are by far the most commonly encountered and the only ones for which fuseholders/breakers are still commonly available.<ref>{{cite web|title=Google search on UK availability of Modern breakers for older consumer units|url=http://www.screwfix.com/p/wylex-32a-sp-type-b-curve-mcb/87979|publisher=Screwfix|access-date=5 March 2016}}</ref>

Some manufacturers have added innovative features such as [[CPN Cudis]] who have added a [[LED]] strip light to their 'Lumo' consumer unit to enhance visibility in dark locations such as under staircases.<ref>{{cite web|title=Innovative Bury company recognised with three award nominations|url=http://www.burytimes.co.uk/news/business/11608891.Innovative_Bury_company_recognised_with_three_award_nominations/|website=www.burytimes.co.uk|access-date=6 May 2015}}</ref>

==== RCD protection types ====
[[File:RCD Protection Consumer Dual Split-Load.jpg|thumb|Modern RCD Protection Consumer Dual Split-Load]]

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.

Consumer units have different methods of protecting circuits. For example, a dual split-load consumer unit can be arranged in a two-story dwelling as follows:

RCD 1

*Upstairs Lights,
*Downstairs Ring Final,
*Garage Sockets,
*Cooker

RCD 2

*Downstairs Lights,
*Upstairs Sockets,
*Shower,
*Heating

By arranging the circuits like this, power will still be present on one of the floors if only one RCD trips out. Moreover, having sockets and lights on alternate RCD's means that if a faulty kettle downstairs trips that RCD for example, the kitchen lights will still be available, avoiding the hazard of investigating the fault in darkness.

Another way to protect circuits under the 17th Edition IET Wiring Regulations is by fitting Residual Current Circuit Breaker With Overload (RCBOs) to every circuit, and although this is more costly than the RCD+MCB's option, it means any fault condition on a circuit trips only that circuit's RCBO, so the search for the fault is narrowed down from the start. When an electrician must be called out, this localised fault can be resolved faster (and therefore cheaper) in contrast with the RCD+MCB's arrangement, which only indicates a fault somewhere within that RCD's set of circuits.

Some older systems such as those that use MK or old MEM Consumer Units that had one fuse per spur, so for instance:

*Upstairs Lights Fuse 1
*Upstairs Sockets Fuse 2
*Downstairs Lights Fuse 3
*Downstairs Sockets Fuse 4
etc..

===Legacy fuseboxes===
A small number of pre-1950 fuseboxes are still in service. These should be treated with caution because exposed live parts are common on these boxes. The installations they supply will not meet modern standards for [[Earthing system#Safety|electrical safety]]. Another characteristic of very old installations is that there may be two fuses for each circuit; one on the [[Electrical wiring|live]] and one on the [[Ground and neutral|neutral]]. In rare instances, old ring circuits may be encountered with no fewer than 4 15&nbsp;A fuses per ring, one on each of L and N, and this duplicated for each of the two feeds for the ring.