Consumer units are common to almost every premises. For such a commonplace piece of equipment, there remain many areas of concern with their installation. In this article, Jake Green, Head of Technical Engagement with Scolmore Group, considers some of the factors to be considered for both surface-mounted and recessed consumer units.
All consumer units are, by definition, a distribution board suitable for operation by ordinary persons. The standard to which all consumer units conform is BS EN 61439-3, and this standard applies to any consumer unit whether it is surface-mounted or buried within the fabric of the building.
Beyond the requirements of BS EN 61439-3 there are additional requirements to be considered in BS 7671 and Building Regulations.
Requirement B3 of Approved Document B1 (Domestic) covers the internal fire spread of structures. The intention of B3 is, amongst other things, to ensure that load-bearing structure withstands the effects of fire without the loss of stability, that openings in fire-separating elements are protected to maintain continuity of the fire separation, and there is inhibition of the unseen spread of fire and smoke in cavities.
Regulation 527.1.1 (Precautions within a fire-segregated compartment) in BS 7671 requires that the, ‘…risk of spread of fire shall be minimised by the selection of appropriate materials and erection in accordance with Section 527.’
Furthermore, in domestic premises, Regulation 421.1.201 requires consumer units conforming to BS EN 61439-3, and similar switchgear assemblies, to either have their enclosure manufactured from non-combustible material or enclosed in a cabinet or enclosure constructed of non-combustible material. It is because of this regulation that consumer units in the UK are made of steel.
The installation of both surface-mounted and recessed consumer units must take account of these requirements.
Cable entry for surface-mounted consumer unit
Cables entering a surface-mounted consumer unit either from the top or bottom do not breach any requirements found in the Building Regulations. However, Regulation 416.2.2 does require that the horizontal top surface of a readily accessible barrier or enclosure has a degree of protection of IPXXD or IP4X. All other live parts must be behind enclosures or barriers providing at least IPXXB or IP2X (416.2.1). Surface-mounted consumer units do not need to be ‘sealed’, typically with the use of intumescent seals.
Cables entering from the rear of a brick/block-built wall require no sealing against fire spread from within the consumer unit as no fire risk exists.
However, an installer having cables entering the rear of a surface-mounted consumer unit installed on a stud wall is likely to have caused a significant breach of the building fabric. Whilst a stud wall is unlikely to be load-bearing, it may be acting as a fire barrier. Where such a breach is within a stud wall, and a fire barrier has been breached, the building fabric may no longer inhibit the spread of fire to the degree necessary and an intumescent seal may need to be considered for the rear entry knockout.
Cable entry for recessed consumer unit
As with a surface mounted consumer unit installed on a brick/block load-bearing wall, a recessed consumer unit requires no sealing other than that required by Regulation 416.2.1 (IPXXB/IP2X). This is because all cables entering the consumer unit are buried within a wall which is inherently fire-resisting, and so no additional precautions are required.
Where a recessed consumer unit is installed within a stud wall which acts as a fire barrier, care should be taken to ensure that the consumer is sealed against the spread of fire. Whilst the risk of fire is small, the consequences of such a fire could be grave and so additional precautions should be taken.
Conclusion
There is no uniform approach to the installation of a consumer unit. Care should be taken to meet the requirements of the Building Regulations, as well as the relevant parts of BS 7671.
This article was published in the January 2025 issue of Electrical Contracting News.
