Why Plastic Fuse Boards Are Not Always an Automatic EICR Failure

Where the Concern About Plastic Boards Comes From

The concern about plastic consumer units originates from an amendment to BS7671 (the 17th Edition Amendment 3, which came into effect in 2016) that introduced requirements for consumer units in domestic properties to have their enclosure manufactured from non-combustible material, or be enclosed in a cabinet made of non-combustible material.

The rationale is that a plastic consumer unit, if subjected to sustained arcing or overheating internally, can ignite and contribute to a fire. A metal-encased board offers better fire containment. This is a legitimate concern, particularly in properties with older protective devices that may not respond quickly to certain types of fault.

What the Regulation Actually Requires

The requirement for non-combustible enclosures applies to new consumer unit installations from 2016 onwards. It means that any consumer unit installed after that date must meet the standard. Consumer units installed before 2016 were compliant with the regulations at the time of installation.

Crucially, the requirement for non-combustible enclosures is not retrospective in a way that automatically makes all pre-2016 plastic boards non-compliant. An inspector cannot record a plastic consumer unit installed in 2010 as a C2 simply because it is plastic.

When a Plastic Consumer Unit May Be Coded as a C3

In most cases, a plastic consumer unit that is in good physical condition and fitted with appropriate protective devices will be recorded as a C3 — an improvement recommended. This reflects the gap between the older standard under which it was installed and the current best practice, without suggesting that the board presents an immediate or potential danger.

A C3 does not make the EICR Unsatisfactory. A report that records a plastic consumer unit as C3 but finds no other significant observations can still be Satisfactory.

When a Plastic Board Might Be Coded More Seriously

In these circumstances, the coding would be based on the specific condition observed, not simply the material of the enclosure.

• Physical damage to the enclosure — cracks, scorch marks, or signs of overheating
• Evidence of arcing inside the board — discolouration, melted components, burning smell
• Protective devices that are clearly failing, showing signs of thermal damage, or are significantly overloaded
• Missing blanks on the board face that leave live busbars exposed
• An installation where the board is in a particularly high-risk location, such as a garage or outbuilding with combustible materials nearby

The Board Replacement Decision

For landlords with plastic consumer units in their rental properties, the practical question is whether to replace the board proactively or wait until an EICR recommends it. There are arguments both ways.

Replacing a plastic board with a modern metal-encased unit fitted with Type A RCBOs on all circuits is a genuine improvement in safety and will remove any observation relating to the board type. If the board is old, if the property has had EICRs with recurring observations about protective device type or board condition, or if a rewire or significant remedial works are being planned anyway, including a board replacement in that scope makes sense.

If the board is in good condition, all protective devices are working correctly, and the EICR records only a C3 for the board material, there is no legal obligation to replace it immediately. The decision becomes one of investment planning rather than regulatory compliance.