What is a metal consumer unit (Amendment 3)?

Glossary · Consumer units and protection

How the metal consumer unit rule works

The IET says the requirement for non-combustible consumer units arrived in the 17th Edition of the Wiring Regulations, BS 7671:2008+A3:2015. The current rule says consumer units and similar switchgear in homes must be made from non-combustible material or be enclosed in a cabinet made from non-combustible material.^{[1]IET, BS 7671 FAQs: Consumer Units and Protective Devices} In practice that means a metal unit, or a unit in a metal cabinet.

The IET says the rule applied from January 2016. Its aim is to contain any fire within the enclosure, limit its spread and remove the plastic as an additional fuel. The IET adds that there is substantial evidence that a plastic unit with a deficiency, such as a loose connection, can burn and release toxic gases. The risk is greater where the unit is on an escape route, such as a hallway or under the stairs.^{[2]IET, Consumer units: safe fuse-box upgrades for modern homes}

NICEIC lists the rule among the requirements for installing a consumer unit in a home. It adds that cables entering the unit must be protected from abrasion and sharp edges.^{[5]NICEIC, Consumer units and fuse boxes: installation and replacement}

A note on names. “Amendment 3” in this context means the 2015 amendment to the 17th Edition. A different “Amendment 3” to the 18th Edition was published in 2024, and it has since been superseded by Amendment 4, which NICEIC says became the only version of the standard on 15 October 2026.^{[6]NICEIC, Understanding BS 7671:2018 + Amendment 4:2026}

What the rule means for an existing plastic unit

The rule applies to new work. It does not condemn units already in homes. Electrical Safety First says a consumer unit need not be replaced because its enclosure is made of combustible material such as plastic, in light of Amendment 3 to the 2008 edition of BS 7671.^{[3]Electrical Safety First, Best Practice Guide 1: Replacing a consumer unit in residential and similar premises} The same guide says there is no legal requirement to upgrade an existing installation to current standards.^{[3]Electrical Safety First, Best Practice Guide 1: Replacing a consumer unit in residential and similar premises}

On an inspection, NICEIC’s best practice guide gives a C3 (improvement recommended) to a combustible unit that is not inside a non-combustible enclosure and is under a wooden staircase or on the sole route of escape. Elsewhere the guide lists it as a non-conformity that does not give rise to danger and does not need to be recorded on the report.^{[4]NICEIC, Best Practice Guide 4: Electrical Installation Condition Reporting, Issue 7} NICEIC says a C3 does not make an EICR unsatisfactory.^{[7]NICEIC, Electrical Installation Condition Reports (EICRs)} See EICR observation codes.

Metal enclosures and earthing

A metal unit has its own points to get right. The IET says nothing prevents a metal unit being used with a TT earthing system. It warns that an earth fault must not be allowed to develop between the meter tails and the metal enclosure before the RCD. Ways to reduce the risk include short meter tails and proper clamps and glands.^{[1]IET, BS 7671 FAQs: Consumer Units and Protective Devices} That design work belongs to a registered electrician. See earthing systems.

Replacing a consumer unit is notifiable work under Part P in England and Wales, so it must be done by a registered electrician or notified to building control.^{[5]NICEIC, Consumer units and fuse boxes: installation and replacement}

Example

Karen buys a 1990s semi in Pudsey with a white plastic consumer unit in the cupboard under the stairs. The stairs are carpeted wood. Her EICR records the plastic unit as a C3 improvement. The report is still satisfactory.

She asks about the unit. Her electrician explains the rule and that replacing it is her decision. She chooses to do it at the same time as other work. The electrician issues the certificates for the new unit.

What people get wrong

The commonest mistake is believing a plastic consumer unit is illegal or fails an inspection by default. It does not. The 2016 rule applies to new work, and an existing plastic unit is only coded where it sits under wooden stairs or on the sole escape route.

The reverse mistake is believing a metal unit alone makes the board safe. The enclosure contains a fire. It does not do the work of RCDs, circuit breakers or an AFDD, and it still needs correct connections.

The bottom line

A metal consumer unit meets the rule, in place since January 2016, that home units must be non-combustible so that a fire stays inside the box. Existing plastic units do not have to be replaced for that reason alone. A plastic unit under a wooden staircase is a C3 on an inspection. Choosing and fitting a unit is for a registered electrician. See consumer unit upgrades.