Editing Distribution board (section)

===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..