Consumer units

Definition

A consumer unit is defined by BS 7671:2008+A3:2015, the IET Wiring Regulations, as “a particular type of distribution board comprising a type-tested co-ordinated assembly for the control and distribution of electrical energy, principally in domestic premises, incorporating manual means of double-pole isolation on the incoming circuit(s) and an assembly of one or more fuses, circuit-breakers, residual current operated devices, or signalling and other devices proven during the type-test of the assembly as suitable for such use.” A consumer unit may also be known as a consumer control unit or electricity control unit and may often still be referred to as a fuse box (old term).

Technical overview

A consumer unit ordinarily controls and distributes power to electrical accessories and equipment in a dwelling, including circuits for socket-outlets, lighting circuits, cookers, showers and anything else that requires an electrical supply. It is common for modern consumer units either to have:

• individual residual current circuit-breakers with overcurrent protection (RCBOs) for each circuit; or
• a split load system where two or more residual current circuit-breakers (RCCB) each protects a group of circuits. Should one RCCB operate, other circuits would remain live.

Consumer units installed in the UK must also meet the requirements of Regulation 132.12 Accessibility of electrical equipment, e.g. where disabled persons would access the consumer unit in order to reset circuit-breakers, RCCBs or RCBOs.

New regulation 421.1.201

In January 2015, Amendment No 3 to BS 7671:2008 introduced a regulation relating to consumer units. The wording of that regulation is as follows:

421.1.201 Within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS EN 61439-3 and shall:

(i) have their enclosure manufactured from non-combustible material, or

(ii) be enclosed in a cabinet or enclosure constructed of non-combustible material and complying with Regulation 132.12.

NOTE 1: Ferrous metal, e.g. steel, is deemed to be an example of a non-combustible material.

NOTE 2: The implementation date for this regulation is the 1st January 2016, but does not preclude compliance with the regulation prior to that date.

The implementation date for this new regulation was 1 January 2016.

The intent behind the new regulation was to contain, as far as is reasonably practicable, any fire within the enclosure or cabinet and to minimise the escape of flames.

Related articles on Designing Buildings Wiki

• Domestic micro-generation.
• Electrician.
• Electricity supply.
• Energy.
• Feed in tariff.
• Flexible electrical networks for a low carbon future.
• Glossary of electrical terms.
• Microgeneration.
• Micro-grids
• Power over ethernet.
• Power over USB.
• PV inverter.
• Rewiring.
• Switchgear.
• The Future of Electricity in Domestic Buildings.
• Uninterrupted power supply for buildings.
• Utilities.

External references

• IET magazine Wiring Matters publishes industry articles for electricians and installers. The related blog published an updated article about consumer units in January 2016