After replacing a consumer unit, it is found that there is a shared neutral between the upstairs and downstairs lighting circuits. Would it comply with BS 7671 if I put the lighting onto one circuit to avoid the RCD tripping?
The Electrical Safety Council’s Best Practice Guide No 6 (Consumer unit replacement in domestic premises) sets out a procedure to help avoid such foreseeable circumstances.
In any event, the shared neutral situation must be corrected to remove the electric shock hazard.
Preferably each circuit should be provided with its own neutral to satisfy Section 314.
However, where this is not practicable, the two lighting circuits sharing the neutral may be connected to a single protective device (creating a single circuit), provided that the circuit is suitable for the connected load.