A new consumer unit. An old wiring fault.
A board replacement can reveal a problem that was already hiding in the wiring. Here’s what we found when we upgraded this installation to individual RCBO protection.
The fault behind the tripping
On this job, we replaced the existing consumer unit and moved from MCBs to individual RCBO protection. During the work, we uncovered a borrowed-neutral issue between circuits.
An MCB provides protection against overload and short-circuit current. An RCBO combines overcurrent protection with residual-current protection, which checks for an imbalance in the current flowing through the protected circuit’s live conductors.
With a borrowed or incorrectly shared neutral between separately protected circuits, current can return through the wrong circuit. That can cause an RCBO to trip. The new protection has revealed a pre-existing wiring problem; it has not created one.
What the work involved
- Replacing the consumer unit with individual RCBO protection.
- Fitting cement-board backing over the timber before mounting the new equipment, as an added fire precaution.
- Adding a switch-fuse to the supply arrangement because of the length of the tails.
- Carrying out a full Electrical Installation Condition Report (EICR).
- Identifying the borrowed-neutral issue and correcting minor switching faults.
- Completing the installation testing and supplying an Electrical Installation Certificate (EIC).
The backing and switch-fuse were parts of this particular installation. The supply arrangement, protection and mounting requirements need to be assessed for each property.
Why we looked beyond the board
The consumer unit is only one part of an electrical installation. A new board still connects to the existing circuits, so the condition of that wiring matters.
The full EICR on this job helped us assess the existing installation and identify defects. It gave the work a wider focus than simply replacing the equipment visible on the wall. We also corrected the minor switching faults found along the way.
The report and the certificate have different jobs
An EICR records the condition of the existing installation within the agreed inspection scope. An EIC records the installation work carried out and its inspection and test results.
After this board replacement and final testing, the customer received their EIC for their records. Keeping that paperwork makes it easier to understand what work has been completed in the future.
Thinking about a board upgrade?
Send your postcode, a photograph of the outside of your existing consumer unit and a short description of what you need. Keep all electrical covers in place. We can discuss the installation, access and scope before arranging the work.
We carry out consumer unit upgrades, EICRs and electrical testing, and fault finding across Inverness and the Scottish Highlands.
Prefer a form? Send an enquiry through the website.
Technical background and sources
The job details come from Shaun’s account of this completed installation. Technical background was checked on 25 October 2026.