Question. In BS7671 what reg states about proving dead? Also about locking off?

Adhere to the five essential rules (PIPIC) for making low voltage equipment dead and safe to work on.

Evening Chris

Can you think of way and installation could become live with the main switch off and the supply fuses withdrawn?

JP

 Chris Pearson 

Also refer to the EAWR Regulation 4 and the guidance in paragraph 72.

PEN faults, solar panels, batteries poor drawings - hands up if you have ever pulled the wrong fuse on a big site? There may be another incomer for something un-marked.

It is far from impossible for things to be live or worse for them to become live mid-job after all.

And then beyond that, the cases where it is meant to be. Live working may be OK, so long as you can justify it and have the tools and know how to do it well. Of course if not, then  you first slip-up maybe your last.

Mike.

There used to be an excellent video on the IET YouTube channel showing exactly how an installation could be live with the main switch locked off and the DNO fuses removed, however the IET had to take it down because they only had permission to use it for a limited period, which is a real shame as it really was worth watching and extremely informative.

Yes. There is more than one (mains) supply. I recall such an event being mentioned during my training, but not in a domestic installation.

But ...

There could be.

I am in the process of installing a new DB at home. The new one sits adjacent to the old one, but the supplies are different so there is scope for carelessness.

OK. As Mike says, a PEN fault. So next door is still connected and we share the same gas (or water) supply so neutral and earth go up to somewhere near line voltage. Hang on though - I could be touching an ECP without working on the installation.

But then again, both supplies are in plastic and we have no PV on the roof and no EV plugged in on the drive.

Hm?

Chris Pearson said:

It should not be possible for the installation to become live if locked off and the key is in one's pocket

Induced or capacitive coupling from another source (perhaps lighting ... but not always) has been known to take human life !

It's "energization" ...

Chris Pearson said:

There is more than one (mains) supply. I recall such an event being mentioned during my training, but not in a domestic installation.

But ...

There could be.

Island mode ... prosumers' electrical installations ... and other means of energization!

John Peckham said:

Can you think of way and installation could become live with the main switch off and the supply fuses withdrawn?

I can. Even without solar PV and battery storage ...