WHAT IS A CONSUMER UNIT?

A consumer unit is defined in Part 2 of BS 7671 as: ‘A particular type of distribution board intended for operation by ordinary persons, comprising a type-tested co-ordinated assembly for the control and distribution of electrical energy, incorporating manual means of double-pole isolation on the incoming circuit(s) and an assembly of one or more protective devices, signalling and other devices proven during the type-test of the assembly as suitable for such use. This does not preclude the use of consumer units within non-domestic premises.

All consumer units (as defined) in the UK conform to the relevant parts of BS EN IEC 61439-1 and BS EN 61439-3.

BS EN IEC 61439-1: 2021 Low-voltage switchgear and controlgear assemblies Part 1: General rules covers the general definitions, service conditions, construction requirements, technical characteristics, and verification requirements of such assemblies. BS EN 61439-3: 2012 (as amended) Low-voltage switchgear and controlgear assemblies Part 3: Distribution boards intended to be operated by ordinary persons

(DBO) is to be read in conjunction with BS EN IEC 61439-1 and details the specific requirements for DBOs intended to be operated by ordinary persons.

All consumer units, therefore, are a particular type of single-phase distribution board containing, as a
minimum, the following:

• Manually operated double-pole main switch.
• One or more protective devices.
• Additionally, they may contain signalling and other devices.

There are a range of ways in which consumer units are legitimately set up, including:

• Main switch and a split-load consumer unit typically containing two RCCBs and a series of
circuit-breakers for the final circuits.
• Main switch and separate RCBOs for each final circuit.
• Main switch and a mixture of RCBOs and circuit-breakers for each final circuit.