Neutral and earth question

Sure is a while since I've read such an un-engineeringly-structured post as this :-)

That's because this is uk.d-i-y and I am not an engineer. Anyway, the job is now unengineeringly completed :-)

But what did you achieve by removing cables from the earth?

As I thought I explained, there was no way of knowing if the black wire was neutral or earth without specialist equipment / knowledge. The electrician suggested it was therefore safer to isolate it from the back box.

Couldn't the electrician test it for you, he should have had the gear.?

This was done over the phone. It was clear he did not fancy the job. I think he considered he was doing me a favour by suggesting what I should do and avoiding me the cost of a visit.

I didn't see the original post as I just pop into here now and again due to work commitments.

However I did find this an interesting question that you asked.

It's very common and good practice to tie unused cores in cables to earth (they should also be over sleeved with green/yellow). In this case if the "neutral" is using the earth as return path then splitting it from the earth would cause something not to work.

As far as I can see, the back box is earthed only by the black wire (unless is it is attached to conduit, which does not seem to be the case). I do not know where the black wire comes from so it seems to me that I cannot exclude the possibility it is neutral unless I can prove it is earth, which seems to be impossible without disconnecting the neutral at the consumer unit, which I understand I am not allowed to do. The suggestion of the electrician is that there is no need to do this because isolating the steel box is just as good.

strange cable colours crop up unexpectedly where there is dual switching (staircase lighting perhaps). They should be sleeved to denote the actual use.

If I knew the actual use, I would not have asked the question in the first place :-)

Who says?

It's a fudge. An isolated steel box may be acceptable but not ideal.

Place a bulb between live and your black wire. If nothing happens then your black wire is floating. If the light is powered then the black wire is neutral. If your RCD is activated then it is most likely an earth or a borrowed neutral depending on your consumer unit and circuit arrangement.

My money is that it's a neutral which I would terminate with a Wago or choc block.

I would attach the cable to the back box only if I am satisfied it is an earth.

Not recommended maybe rather than not allowed, but the central rule is that the work should be done by a competent person and I would have a challenge on my hands to demonstrate to any insurer that I am a competent person. I don't know how to disconnect an earth wire from the consumer unit safely.

I am tempted to respond 'Who says' but I won't. The electrician I spoke to says it is okay. In what respect is it not?

My understanding is that the light could still be powered if the black wire is earth since in the PEN (protected earthed neutral) system the earth and the neutral are connected together at the point of entry.

This is exactly what I have done, so why is it 'a fudge'?

This is exactly what I have done.

"As I thought I explained, there was no way of knowing if the black wire was neutral or earth without specialist equipment / knowledge."?

That was me (OP) and this was my reason for disconnecting the wire from the back box (after speaking to an electrician).