Why an EICR Should Be Done Before Replacing a Consumer Unit

What the Consumer Unit Replacement Actually Changes

When a consumer unit is replaced, the protective devices connected to your circuits change fundamentally. The old board — whether it had rewireable fuses, older MCBs, or a split-load arrangement with a single RCD — is replaced with a modern unit typically fitted with individual RCBOs, each providing both overcurrent and earth fault protection on a per-circuit basis.

The wiring connected to those devices has not changed. The cables running through your walls, ceilings and floors are the same as they were before. But the protection device monitoring those cables is now considerably more sensitive.

The Risk of Fitting a Modern Board to Untested Wiring

Older wiring — particularly PVC-sheathed cables installed in the 1970s and 1980s, or older rubber-insulated wiring — will have a measurable level of insulation degradation. This is normal for its age. The insulation around conductors becomes less effective over time, particularly where cables have been exposed to heat (such as in loft spaces or near light fittings), damp, or physical damage.

A modern RCBO set to 30mA sensitivity will detect the earth leakage that results from this degradation and trip the circuit. This can happen on lighting circuits, ring main circuits, or any other circuit where the insulation has deteriorated to a point where leakage is measurable.

The practical result is a property where lights trip off, ring main circuits cut out, or specific appliances cause the board to trip — often without any obvious fault that can be identified by looking at the installation.

What an EICR Reveals Before the Work Is Done

An EICR carried out before a consumer unit replacement will include insulation resistance testing on all the circuits in the installation. This testing measures how well each circuit's insulation is performing and identifies circuits where degradation is likely to cause problems with modern protection devices.

Armed with this information, you can make an informed decision. Circuits with acceptable insulation values will work reliably with a new board. Circuits with low insulation resistance values may need remediation — either rewiring, or investigation to establish whether the cause is a specific accessory or appliance rather than the cable itself.

• Insulation resistance testing identifies circuits likely to trip with modern RCBOs
• Earth continuity testing confirms protective conductors are intact
• Loop impedance testing verifies that protective devices will operate correctly
• Visual inspection identifies wiring that is clearly not suitable for continued use
• The inspector can advise on which circuits should be rewired before the new board is fitted

The Cost Argument

Some landlords or homeowners will weigh up the cost of an EICR and decide to proceed directly to the consumer unit replacement without it. In the short term, this saves money. In the medium term, if the new board triggers tripping on circuits with degraded insulation, the diagnostic work and remediation required will typically cost more than the EICR would have.

Worse, the property may not be comfortable to live in while the tripping issues are resolved — which creates tension with tenants and, in a rental context, potential obligation to address the issue under the Landlord and Tenant Act as well as the Electrical Safety Standards.

For Rental Properties: The Regulatory Position

Under the Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020, landlords in England are required to have a valid EICR for every tenanted property, renewed at least every five years. A consumer unit replacement does not satisfy this requirement — it is installation work, not inspection and testing work.

If you are planning a consumer unit replacement on a rental property that doesn't have a current EICR, having the EICR done first serves two purposes: it informs the board replacement with insulation resistance data, and it satisfies your legal compliance obligation. The alternative — board replacement first, EICR later — is a false economy and may still reveal insulation issues that need addressing.