EICR failed because a borrowed neutral was detected

Each final circuit is arranged so that its line and neutral belong together. A borrowed neutral is the name inspectors use when that arrangement has been crossed: the live path is on one circuit and the return is on another. It is often found at a junction, a wrongly connected accessory, or an old alteration.

Read the observation for the circuits named and for where the connection was seen or inferred. If the report also lists a limitation, the inspector has not claimed to have opened every junction.

Protective devices are selected for the circuit they sit on. If the neutral returns elsewhere, a fault current may not pass through the device the designer expected. An RCD or RCBO can then fail to see the imbalance that should disconnect the circuit.

Isolation is the other practical problem. Switching off one circuit can leave a neutral that is still connected to a live circuit. Equipment that looks isolated may not be. That is a reason to treat the observation seriously. It is not, by itself, a rule that the code must be C1.

C1, C2, C3 and FI describe the inspector's judgement of the condition that was found. A confirmed dangerous live part can be C1. A potentially dangerous borrowed neutral can be C2. Partial evidence, or a junction that could not be opened, can be FI. Under the current A4:2026 EICR format, an FI observation is advisory and does not by itself make the overall assessment unsatisfactory.

Do not treat a borrowed neutral as automatically unsatisfactory, and do not treat it as automatically C3. The same words on two reports can sit next to different codes because the installations are not the same.

Continuity, polarity and the behaviour of the circuit under test can point to a crossed neutral. The inspector may also see the joint if access was agreed. A sample inspection does not prove that every other joint is sound.

Everyday clues, such as a light that changes when another circuit is loaded, are a reason to ask for investigation. They are not a diagnosis, and they are not a substitute for the report.

Send the whole report, the observation number, and the circuit names. Say which rooms were recently altered. A quotation for tracing is not the same as a quotation for a repair, and opening floors or ceilings may be a separate item.

For a specified tenancy in England, whether any further work has a statutory period depends on regulation 3(4), not on the words borrowed neutral. That explanation is on the unsatisfactory EICR page.