Metal consumer units became mandatory under the 18th Edition as part of a wider push for improved fire containment and safer domestic distribution boards. The change caught a lot of installers off guard at the time, but the reasoning behind it is simple: plastic boards were allowing fires to spread, while metal units can contain heat long enough to prevent escalation.
Quick Answer: The 18th Edition requires consumer units to be made from non-combustible material - typically steel - to stop electrical faults from turning into property fires. Metal enclosures slow fire spread, contain heat, reduce ignition risks, and offer far better protection where cables, terminals, and terminations are running hot.
This guide explains the regulation change in plain language, what it means on-site, and which metal units installers choose for domestic and light commercial setups.
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Why Did the 18th Edition Make Metal Consumer Units Mandatory?
The change wasn’t arbitrary. Before Amendment 3 of the 17th Edition and continuing into the 18th Edition, the industry saw a sharp rise in fire incidents linked to domestic consumer units. Investigations highlighted common causes:
- Loose terminations causing overheating
- Poor-quality plastic boards melting under load
- Ageing breakers and RCDs running hot
- Boards installed under stairs or escape routes
Plastic enclosures, especially older ABS ones, could ignite or deform when exposed to heat. Metal enclosures don’t stop a fault—but they contain it long enough to prevent a small overheat event from becoming a domestic fire.
What Are the Benefits of Metal Consumer Units?
While the regulation change is primarily about fire containment, metal boards offer several practical advantages on-site:
- Better fire resistance – steel doesn’t ignite or melt under fault conditions
- Superior thermal stability – terminals and breakers stay protected even if something overheats
- Stronger enclosures – lids and bases don’t warp, improving fit and finish
- Improved cable entry strength – metal knockouts withstand more handling than plastic
- Compliant install evidence – an easy tick on EIC inspection sheets
Modern metal consumer units also offer cleaner internal layouts and more stable DIN rail mounting, which subbies appreciate during fast swaps.
What Does the 18th Edition Actually Require?
The regulation text states that consumer units installed in domestic premises must be constructed from “non-combustible materials.” In practice, this means:
- Enclosure must be metal (steel is standard)
- Internal components can still be plastic (RCBOs, breakers, supports)
- Lid and base must be metal
- Cable entry points must maintain fire resistance
- Positioning must avoid escape routes where possible
Regulation Note: The 18th Edition does not ban plastic consumer units outright - but if used, they must be enclosed inside a separate fire-rated cabinet. For most installs, a metal board is the simplest compliant choice.
What Does This Mean for Installers?
From an installer’s point of view, metal boards don’t radically change the job, but they do influence a few areas:
- Stronger mounting – metal boards are heavier and need secure fixing points
- Cable entry is cleaner – knockouts are more predictable
- Fire containment is built in – fewer concerns about placement
- Better inspection pass rate – no discussion with assessors
Modern metal boards are also laid out in a way that makes RCBO-based installs far easier than older plastic units, especially where you’re running high R1+R2 circuits or multiple unbundled neutrals.
Recommended Metal Consumer Units
Power & Data UK stocks a range of metal twin-RCD consumer units designed for fast domestic swaps, new installs, and RCBO conversions. These are popular with installers because they offer clean layouts, solid enclosures, and no-fuss knockout placement.
- Twin RCD Metal Consumer Unit – WME22100TR-SP
- Twin RCD Metal Consumer Unit – WME1663TR-SP
- Twin RCD Metal Consumer Unit – WME2280TR-SP
- Twin RCD Metal Consumer Unit – WME2280TR
- Twin RCD Metal Consumer Unit – WME22100TR
Browse the full category: Metal Consumer Units
FAQs
Installers regularly ask practical questions about metal boards and how the 18th Edition affects their day-to-day work. Here are the most common ones.
Are plastic consumer units now banned?
No. They must simply be enclosed within a fire-rated cabinet or installed in a non-domestic location where the rule doesn’t apply.
Why do metal boards help prevent fires?
They contain heat and flames long enough to stop ignition spreading to surrounding materials, giving time for breakers to trip.
Can I still use plastic enclosures for outbuildings?
Only if they are inside a separate fire-rated enclosure. In practice, metal units are now standard for garages and outbuildings too.
Do metal consumer units improve inspection outcomes?
Yes - assessors typically check enclosure type early in the EIC review. Metal boards remove ambiguity.
👉 Ready to upgrade or replace a board? Browse all Metal Consumer Units