Metal Consumer
Unit Requirements
Why UK consumer units must be metal in 2026, what BS 7671 Section 421.1.201 actually says, why the rule was introduced plus how it applies to existing plastic boards still serving in many homes.
UK domestic consumer units installed since 1 January 2016 must have a non-combustible enclosure. The rule comes from BS 7671 Section 421.1.201 introduced in Amendment 3 to the 17th Edition. In practice this means a steel enclosure. The rule applies to new installs plus full replacements. Existing plastic boards already in service are not retrospectively illegal but cannot be replaced like-for-like with another plastic board on a compliant install today.
Four figures
worth knowing
These four references frame every compliant metal consumer unit install in the UK in 2026.
Mandate Year
Amendment 3 to BS 7671 17th Edition came into force on 1 January 2016. From that date all new domestic consumer units required non-combustible enclosures.
BS 7671 Section
Section 421.1.201 sets the rule. Sits inside the larger Section 421 which covers protection against thermal effects.
Standard Material
Steel is the practical default. The rule technically allows any non-combustible material but steel meets the test plus is the only option manufacturers ship.
Notifiable Work
Replacement is always notifiable under Part P. Like-for-like swap of a plastic board with another plastic board is non-compliant on a new install.
Four things every metal
enclosure must satisfy
The 2016 rule is short but specific. A compliant metal consumer unit install must satisfy four things in practice.
Non-Combustible Material
The enclosure must not contribute to fire spread. In practice steel. GRP is technically allowed but rarely used. Plastic boards no longer qualify.
Manufacturer Type Test
Each enclosure carries a manufacturer type test certificate. Devices fitted must be compatible. Mixing brands voids the type test plus the compliance.
Mounting on Combustible Surface
Mounting on or in a combustible surface (timber, hardboard) needs additional fire-protective separation in line with the manufacturer's instructions.
Certified Install
Install carried out by a Part P registered electrician. EIC issued. Building Control notified. Paperwork chain complete on handover.
The metal mandate exists because plastic boards were starting fires
Before 2016, almost every UK domestic consumer unit was plastic. By the early 2010s the London Fire Brigade plus other fire authorities started reporting a pattern. Domestic electrical fires were originating inside or close to plastic consumer units. The plastic enclosure was not always the initial cause. It was the contribution to fire spread that mattered. Once a fault inside the box raised internal temperatures sufficiently, the plastic enclosure could itself ignite plus accelerate the fire.
The IET responded. Amendment 3 to the 17th Edition was published in January 2015 plus came into force on 1 January 2016. The amendment added Section 421.1.201: "Within domestic (household) premises, consumer units plus similar switchgear assemblies shall comply with the relevant standard plus shall: (i) have their enclosure manufactured from non-combustible material; (ii) be enclosed in a cabinet or enclosure constructed of non-combustible material plus complying with [the relevant clauses]."
What "non-combustible material" means in practice
BS 7671 does not name a specific material. It defines non-combustible by reference to the European fire classification standards. The practical materials that meet the rule are:
- Steel. The default for every UK manufacturer. Hager, Wylex, Schneider, Crabtree, MK plus all other major brands ship steel enclosures as standard.
- GRP (glass-reinforced polyester). Technically permitted where the formulation meets the non-combustibility test. Rarely seen on domestic installs.
- Ceramic or composite. Specialist applications only. Not used in mainstream UK domestic installs.
In practice if you buy a domestic consumer unit from any UK trade wholesaler in 2026 it will be steel. The rule has effectively made steel the only choice on new installs.
What the rule does NOT do
This is the part most homeowners get wrong. The 2016 rule applies to new installs plus replacements. It does not retrospectively make existing plastic boards illegal. A plastic consumer unit installed before 2016 is not in breach of any law just because it is plastic. It can continue serving the property until natural end of life or until something else triggers replacement.
Where the rule bites is on replacement. If you replace your existing plastic board, the new board must be metal. A like-for-like plastic-to-plastic swap is non-compliant. A registered electrician will not carry one out plus will not issue an EIC for one because doing so would mean signing off a non-compliant install.
How the rule interacts with EICRs
An EICR assesses an existing installation against today's standards. A plastic consumer unit on its own is not automatically a fail. An EICR engineer can mark a plastic enclosure with a C3 code (improvement recommended) noting that the enclosure does not meet the current Section 421.1.201 requirement. C3 codes do not make the EICR Unsatisfactory.
The EICR result moves to Unsatisfactory if the plastic board has additional defects: no RCD protection (C2), visible scorching or melted plastic (C2), missing main bonding (C2) etc. In other words, plastic alone is a recommendation. Plastic plus another fault is normally a fail.
Mounting on combustible surfaces
The metal enclosure rule addresses the consumer unit itself. It does not solve the wider question of fire spread from mounting surfaces. Many UK homes have consumer units mounted on timber backboards, hardboard, MDF or similar. BS 7671 plus the IET on-site guide both require additional fire-protective separation between a metal enclosure plus a combustible mounting surface in line with the manufacturer's instructions.
In practice this means a fire-resistant backing plate, intumescent material or a cement board layer between the metal box plus the timber. Most modern manufacturer enclosures ship with the necessary fire-rated backing built in. Older retrofit installs sometimes miss this detail.
Metal consumer unit
install cost ranges
Every metal enclosure on the market today meets Section 421.1.201. The cost difference comes from the protective devices fitted inside, not the box itself.
Metal Consumer Unit Cost Bands
All bands include a steel enclosure compliant with Section 421.1.201, parts, labour, EIC plus Building Control notification.
Four steps from
plastic to metal
The metal mandate did not appear overnight. Here is the broad sequence that brought Section 421.1.201 into force in 2016.
17th Edition Adopted
RCD protection required on most domestic circuits. Plastic consumer unit installations remain the UK norm at this point.
Fire Brigade Reports
London Fire Brigade plus other UK fire authorities flag a pattern of domestic electrical fires originating in or near plastic consumer units.
Amendment 3 Published
IET publishes Amendment 3 to BS 7671 17th Edition. Section 421.1.201 introduced requiring non-combustible enclosures on new domestic installs.
Mandate In Force
Amendment 3 came into force. From this date all new domestic consumer units fitted in the UK must be metal. Carried forward to the 18th Edition unchanged.
Four facts about
the metal rule
Rule applies to new installs only
An existing plastic board fitted before 2016 is not retrospectively illegal. The rule bites on the next replacement, not on the existing install.
Plastic alone is normally a C3
An EICR engineer can mark a plastic enclosure with C3 (improvement recommended). C3 does not make the EICR result Unsatisfactory.
Steel is the practical default
The rule allows any non-combustible material. UK manufacturers all ship steel. Buying a domestic consumer unit means buying a steel one in 2026.
Watch the mounting surface
A metal box on a timber backboard still needs fire-protective separation. Modern manufacturer enclosures ship with the right backing built in.
Consumer Unit Upgrades in Milton Keynes
C-Lec Electrical fits BS 7671 compliant metal RCBO consumer units across Milton Keynes, Bedford plus the surrounding Bedfordshire area. Every install certified to Section 421.1.201, EIC issued plus Building Control notification handled in full.
Metal enclosure vs
plastic enclosure
The 2016 rule changed the answer here. Plastic was the UK norm for decades but is no longer fit for new installs.
Compliant 2026 standard
- ✓Non-combustible per Section 421.1.201. Will not contribute to fire spread.
- ✓Compliant on every new install plus replacement under BS 7671:2018+A2:2022.
- ✓Manufacturer type-tested with matched device range giving consistent fault performance.
- ✓EICR clean on the enclosure itself. Any defects flagged are device or wiring related, not enclosure.
- ✓25 to 30 year service life expectation on a properly fitted steel board.
Pre-2016 install
- ✗Combustible material can support fire spread. The reason the rule was changed in 2016.
- ✗Not compliant on new installs or like-for-like replacements since January 2016.
- ✗C3 advisory on EICR by default. Becomes C2 (Unsatisfactory) if combined with other defects.
- ●Existing plastic board fitted before 2016 is not retrospectively illegal. Continues serving until natural end of life.
- ●Will be flagged by surveyors during property sale plus by EICR engineers regardless of EICR overall result.
For the wider context on consumer unit types, RCDs, AFDDs plus the regulations behind all of this, head back to our full guide to consumer units where every common homeowner question is answered in one place.
Back to the Consumer Units Guide
This article sits inside our complete Consumer Units knowledge base. The hub covers everything from board types plus RCBOs through to landlord requirements plus BS 7671 wiring regulations.
More on consumer
unit standards
To understand the full BS 7671 framework that includes Section 421.1.201, our deep dive on consumer unit wiring regulations walks through every relevant section of the 18th Edition Amendment 2. To compare the two enclosure types side by side, our explainer on plastic vs metal consumer units covers cost, lifespan plus EICR behaviour. To understand what specifically triggers an EICR fail on a plastic board, see does a plastic consumer unit fail an EICR. If you need a fully compliant metal board fitted in Milton Keynes or Bedford, our consumer unit upgrades service page is the fastest route to a quote.