Consumer unit change

[shanky887614]

Would you not find the fault before hand unless you did the R1 + RN continuity test on that particular circuit? How often do people do the R1 + RN test?

most electricians will on older properties.

you use to have a N+E cable between each light and seperart L etc to switch and back.

now if they put the live from downstairs lights to switch then upto light on stairs it can cause this issue.

how you test varies depending on visual inspection

 

[baldsparkies]

People living in Ivory towers !!
Luckily there are electricians out there who thankfully live in the real world.
A borrowed neutral on 2 way lighting is an unfortunate by product from by gone practices.
Left untouched in its original form it posed little problems, and guess what, you wont find many fatally electrocuted customers living in properties wired this way.
It was compliant with the regs of the time.
Whats important is that you do not feed the borrowed neutral circuits from different mcb's.
That would leave the installation with a potentially dangerous condition.
In an ideal world you would rewire the offending lighting circuit for compliance with current regs.
And make the customer aware of the requirement.
If for some reason this is not an option, ie customer refuses point blank because of costs and or disruption to decorations.
Well you could walk away !!
Which would leave those suggesting you do so, to move in and wire the lighting circuits onto 1 mcb effectively making them one circuit and in doing so removing a shared neutral scenario.
Of course you should list this as a departure, and make your comments on the existing installation as to the if's what's and whys.
Its your choice and a judgement call as a qualified sparks.
What it isn't, and never has been, is a shock horror, lets be drama queens run forest run scenario.
Presumably you are with a scheme provider considering a board change is notifiable and if your going to building control on your own back,it will cost you lots of ££££s
So if in doubt just phone there technical helpline and ask there advice.
They will give you exactly the same options as I have mentioned above, and at least that way you are getting sensible, and practical advice.
Forums are only as good as the people using them so be careful, and always get advice from qualified trusted sources as a cross check.
Hope that helps.

 

[baldsparkies]

what you have to do is put both lighting circuits onto the same RCD. preferably also on the same MCB.

As an example to the OP, THIS is advise from someone who knows what he's talking about.

With time and experience you get to know the difference.

 

[davesparks]

A borrowed neutral on 2 way lighting is an unfortunate by product from by gone practices.
Left untouched in its original form it posed little problems, and guess what, you wont find many fatally electrocuted customers living in properties wired this way.
It was compliant with the regs of the time.
.

How do you know it was compliant with the regs of the time? I can't find anything in the 13th or 14th which allows it.

 

[shanky887614]

People living in Ivory towers !!
Luckily there are electricians out there who thankfully live in the real world.
A borrowed neutral on 2 way lighting is an unfortunate by product from by gone practices.
Left untouched in its original form it posed little problems, and guess what, you wont find many fatally electrocuted customers living in properties wired this way.
It was compliant with the regs of the time.
Whats important is that you do not feed the borrowed neutral circuits from different mcb's.
That would leave the installation with a potentially dangerous condition.
In an ideal world you would rewire the offending lighting circuit for compliance with current regs.
And make the customer aware of the requirement.
If for some reason this is not an option, ie customer refuses point blank because of costs and or disruption to decorations.
Well you could walk away !!
Which would leave those suggesting you do so, to move in and wire the lighting circuits onto 1 mcb effectively making them one circuit and in doing so removing a shared neutral scenario.
Of course you should list this as a departure, and make your comments on the existing installation as to the if's what's and whys.
Its your choice and a judgement call as a qualified sparks.
What it isn't, and never has been, is a shock horror, lets be drama queens run forest run scenario.
Presumably you are with a scheme provider considering a board change is notifiable and if your going to building control on your own back,it will cost you lots of ££££s
So if in doubt just phone there technical helpline and ask there advice.
They will give you exactly the same options as I have mentioned above, and at least that way you are getting sensible, and practical advice.
Forums are only as good as the people using them so be careful, and always get advice from qualified trusted sources as a cross check.
Hope that helps.

how is having them fed from different mcb's a problem? if there on the same double pole rcd then the N wont be disconnected without the L anyway.

remember the N are usually commoned together

 

[shanky887614]

How do you know it was compliant with the regs of the time? I can't find anything in the 13th or 14th which allows it.

under the 13/14th you would only have 1 neutrel bar so they are all linked so would make no difference if it was fed from another mcb, not good practise but not against the regs of the time as far as im aware

 

[Leesparkykent]

how is having them fed from different mcb's a problem? if there on the same double pole rcd then the N wont be disconnected without the L anyway.

remember the N are usually commoned together

errm Shanky was you on the beer last night or something when you wrote this? Lol :dizzy2:

 

[shanky887614]

errm Shanky was you on the beer last night or something when you wrote this? Lol :dizzy2:

no i was on the whisky at relatives

 

[davesparks]

under the 13/14th you would only have 1 neutrel bar so they are all linked so would make no difference if it was fed from another mcb, not good practise but not against the regs of the time as far as im aware

You still only have one neutral bar but borrowed neutrals are just as bloody dangerous.
The last time I came across borrowed neutrals was between 2 adjacent TPN boards, live taken from one board and neutral from the other.

 

[IzzyS]

under the 13/14th you would only have 1 neutrel bar so they are all linked so would make no difference if it was fed from another mcb, not good practise but not against the regs of the time as far as im aware

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.

 

[Leesparkykent]

no i was on the whisky at relatives

Happy days

 

[derbylad]

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.

that's why you should knock the main switch off.

 

[Pete999]

that's why you should knock the main switch off.

Knock off the main switch? don't you mean carry out the safe isolation procedure? lol sent with humor in mind.

 

[IzzyS]

that's why you should knock the main switch off.

Doesn't help when there are multiple distribution boards and you can't shut down production.

Borrowed neutrals are not limited to domestics.

 

[davesparks]

that's why you should knock the main switch off.

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!

 

[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.