Plastic vs Metal
Consumer Units
The 2016 regulatory shift to metal consumer units, what BS 7671 actually requires plus what an existing plastic board means for your home in 2026.
Since 1 January 2016 all new consumer units fitted in domestic premises in the UK must have an enclosure of non-combustible material. In practice this means steel. Section 421.1.201 of BS 7671 (added in Amendment 3 of the 17th Edition, retained through to BS 7671:2018+A2:2022) is the rule. An existing plastic consumer unit fitted before 2016 is not retrospectively illegal but it is normally coded C2 or C3 on an EICR depending on its other features. New installs and replacements must use a metal enclosure.
Three figures
worth knowing
Mandate Date
1 January 2016. Amendment 3 of the 17th Edition introduced Section 421.1.201 requiring non-combustible enclosures on domestic CUs.
BS 7671 Section
Section 421.1.201 sets the non-combustible enclosure rule. Steel is the practical material that meets the requirement on domestic boards.
Glow-Wire Test
Steel enclosures pass the BS EN 60695-2-11 glow-wire test at 960°C. Plastic enclosures typically fail at this temperature plus can ignite plus contribute to fire spread.
Four steps to the
2016 mandate
The shift from plastic to metal did not happen overnight. The mandate was the end of a four-step regulatory plus investigative process that began in the late 2000s.
Plastic Standard
Plastic consumer units were the UK domestic standard from the 1990s through to the late 2000s. Compliant under earlier editions of BS 7671. No enclosure-material requirement existed.
Fire Reports
London Fire Brigade plus the Electrical Safety Council published evidence of consumer unit fires originating in plastic enclosures. Loose terminations heating up plus igniting the enclosure were the leading mechanism.
Amendment 3 Published
BS 7671 Amendment 3 to the 17th Edition published. Introduced Section 421.1.201 requiring non-combustible enclosure material on consumer units within domestic premises.
In Force
Amendment 3 came into mandatory force on 1 January 2016. Every new domestic consumer unit installed in the UK from that date forward had to be metal. The rule has been carried forward unchanged through every subsequent edition plus amendment.
How they compare
line by line
Eight features that distinguish the two enclosure types in real-world UK domestic use.
The mandate is about fire spread not electric shock
It is worth being clear about why the rule changed. The 2016 mandate was not driven by a sudden discovery that plastic enclosures fail electrically. They do not. A plastic consumer unit fitted plus maintained correctly is just as electrically safe as a metal one in normal operation. Both contain the same protective devices. Both interrupt faults the same way. The rule change was driven by what happens when something does go wrong.
The dominant fault mode that triggered the regulatory move was a loose termination heating up gradually inside the consumer unit over months. A loose neutral or earth conductor at the busbar develops a high-resistance joint. Resistive heating raises the local temperature. The temperature climbs slowly until either:
- The conductor insulation melts plus a short circuit develops, which the MCB or RCBO clears safely (good outcome).
- The plastic enclosure adjacent to the hot terminal ignites before the upstream fault becomes detectable (bad outcome).
Investigative work by the London Fire Brigade plus the ESC documented enough cases of the second outcome between 2010 plus 2014 to drive the regulatory change. The exposed copper conductor inside a steel box cannot ignite the steel. The same exposed copper inside a polycarbonate box can ignite the box, then the surrounding fabric of the property.
What this means for your existing plastic board
The first thing to be clear about: your existing plastic consumer unit is not a fire waiting to happen. The vast majority of UK plastic consumer units installed in the 1990s plus 2000s have operated for decades without incident. The 2016 mandate is precautionary. It removes a specific failure mode from the population by requiring future installs to use a non-combustible enclosure.
The practical position for an existing plastic board is:
- It cannot be replaced with another plastic unit. If yours fails or needs upgrading the new unit must be metal.
- It is normally coded C3 on an EICR. "Improvement recommended" but not Unsatisfactory. Most plastic boards with otherwise compliant features pass an EICR overall with a C3 advisory.
- It can be coded C2. If the plastic enclosure is combined with other defects (signs of overheating, missing main bonding, no RCD protection, exposed live conductor) the EICR result is normally Unsatisfactory.
- It triggers replacement on alteration or addition. Adding any new circuit, replacing the unit itself or fitting an EV charger forces an upgrade to metal.
Why steel was the practical choice
BS 7671 Section 421.1.201 specifies a non-combustible enclosure but does not name the material. In principle a ceramic enclosure or a fibreglass-reinforced one could meet the requirement. In practice the entire UK consumer unit industry standardised on powder-coated mild steel for two reasons:
- Steel meets the glow-wire test cleanly plus is established as a switchgear material in commercial plus industrial boards. The supply chain plus manufacturing process were already in place.
- Steel allows the same physical dimensions plus busbar layouts as the plastic enclosures it replaced. Existing wiring plus fixings transfer to the new unit without redesign.
Modern UK domestic consumer units fitted in 2026 are universally steel. White or grey powder-coated finishes are most common. Some manufacturers offer matt black finishes for a more modern appearance, particularly where the unit is visible in the property.
Four things every homeowner
should know
Plastic is not retrospectively illegal
Existing plastic boards fitted before 2016 remain legal. The mandate applies only to new installs from January 2016 onwards.
EICR result depends on context
Plastic alone is normally C3. Combined with other defects (overheating, no RCD) it becomes C2 plus the report becomes Unsatisfactory.
The mandate is about fire spread
Loose terminations heating gradually inside the enclosure was the failure mode. Steel cannot ignite the way plastic could.
Replacement always means metal
Any consumer unit fitted in 2026 must have a non-combustible enclosure. Plastic-to-plastic replacement is not permitted.
Metal Consumer Unit Upgrades in Milton Keynes
C-Lec Electrical replaces old plastic consumer units with BS 7671 compliant steel enclosures across Milton Keynes, Bedford plus the surrounding Bedfordshire area. Section 421.1.201 compliant. Full EIC plus Building Control notification on completion.
For the wider context on consumer units, RCBOs, AFDDs plus the regulations behind UK distribution boards, head back to our full guide to consumer units where every common 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 choices
To dig deeper into the metal enclosure rule itself, head to metal consumer unit requirements for the regulatory detail. To understand whether a plastic board fails an EICR in your specific circumstances, see does a plastic consumer unit fail an EICR. To understand the wider BS 7671 framework that drives every modern consumer unit decision, see consumer unit wiring regulations. If you need a metal consumer unit fitted in Milton Keynes or Bedford, our consumer unit upgrades service page is the fastest route to a quote.