Does that mean that you believe that any work undertaken on a lighting circuit in some other room invokes the need to RCD protect the circuit if it also supplies a bathroom.
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If you just replaced a light fitting in a bathroom (or, I suppose, just replaced the lamp/bulb!) (without changing the wiring in any way), do you believe that this would generate the need for RCD protection?
More generally, we often see people here being advised that, when extending an existing circuit (of whatever sort), only new buried wiring (and, where appropriate, new sockets) needs to be RCD protected - do I take it that you disagree with that?
As a matter of interest, how are you going to feel next year when the new requirements for CUs come into force? Are you going to interpret the regs as saying that if you undertake any work on any final circuits, that the regs will require that you replace the CU with a 'non-combustible' one?