Consumer unit change

[Risteard]

If I'd done that on the last borrowed neutral if found then if have shut down a six screen cinema complex and part of a shopping centre, I don't think it would have been acceptable!

And I'd have had to shut down a school.

Borrowed neutrals are certainly not something to be excused - it is a dangerous practice and is rightly prohibited.

 

[baldsparkies]

It's been against the regs for at least 35 years, probably longer. And whether it complied or not, it's as dangerous now as it was then.

The problem arises when some poor sod comes along to change, for example, a ceiling rose.

With the MCB off/fuse removed on the circuit being working on, and the circuit proved dead work proceeds.

If there is a load on the other circuit (the one that is sharing the neutral) full line voltage will appear on the neutral as it is pulled from is terminal. It's f***ing dangerous (to electricians, handymen, diyers and anyone else likely to work on it) because safe isolation requires two (or more) MCBs to be turned off.

Under normal circumstances it does not pose any problem to the installation user.

Safe isolation procedures,
The last time I had a belt from a borrowed neutral was back in my wet behind the ears days.
A competent experienced electrician who falls for this old chestnut would get a slap from me for being a ****.
As for Mr Diy working on a domestic 2 way at home, again electricity is not for the inexperienced to be tampering with.
As I have said putting the 2 circuits on the same mcb and Neutral bar is the work around in context with this thread.
Obviously commercial set ups are another ball game and a lesson in taking nothing for granted.
Treat neutral and live with the same respect me says. :wink_smile:

 

[davesparks]

A competent experienced electrician who falls for this old chestnut would get a slap from me for being a ****.

How exactly are you going to include borrowed neutrals in your safe isolation procedure? You isolate and lock off the submain feeding the board you are working on, so all fine and dandy. You remove the board, fit the new one and start connecting up. Somebody switches a lightswitch in another part of the building which operates a light with the neutral borrowed from one of the circuits in the board you are replacing.
Unless you are operating full live working procedures then you don't stand a chance against it.

 

[IzzyS]

And throw in time-switches or photocells for a bit of added excitement. Live working procedures will prevent shocks, but the whole point of my (and others) post is that no-one should think borrowed neutrals are OK in any situation. If you leave it like that then you will be open to prosecution if anyone is subsequently injured.

As I have said putting the 2 circuits on the same mcb and Neutral bar is the work around in context with this thread.

That's fine, as it removes the "borrowed" bit.

 

[Dave OCD]

If they weren't both on the same neutral bar surely you'd have both RCDs tripping constantly anyway ?

 

[davesparks]

If they weren't both on the same neutral bar surely you'd have both RCDs tripping constantly anyway ?

What RCDs? There are no RCDs on the circuits!
For reference the above scenario is based on a real situation. Nobody was hurt as the circuits with the borrowed neutrals were being removed so I had the lives disconnected before stripping the board the neutrals were borrowed from, but it could have been very nasty for someone.

 

[Dave OCD]

My post immediately followed 'Izzys' and was a reply to that.

 

[baldsparkies]

How exactly are you going to include borrowed neutrals in your safe isolation procedure? You isolate and lock off the submain feeding the board you are working on, so all fine and dandy. You remove the board, fit the new one and start connecting up. Somebody switches a lightswitch in another part of the building which operates a light with the neutral borrowed from one of the circuits in the board you are replacing.
Unless you are operating full live working procedures then you don't stand a chance against it.

Agreed, my comments relate to a domestic situation as per my post.
Not to your scenario, which is why that same post concluded with the comment ;

"Obviously commercial set ups are another ball game and a lesson in taking nothing for granted.
Treat neutral and live with the same respect me says."

So provided those comments aren't taken out of context and added to scenarios of your choosing they hold true.

In a domestic single phase environment a qualified spark should not be caught out by borrowed neutrals on a 2 way lighting circuit.
And as others have already stated, myself included, the best course of action if for some reason a circuit re wire isn't an option.
Put both circuits onto 1 mcb (Effectively making it one circuit) with neutrals likewise on the same N bar.

Commercial installs can be a nightmare, thankfully you rarely find situations like the one you mention.
Once a board is isolated, borrowed neutrals tend to show up as you remove the main neutral and check the bar for voltage to earth.
If the circuit is suddenly energised mid board change the airs gonna turn blue, but as said thankfully rare.