Consumer unit change

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stilllearning

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Recently changed a consumer unit and had a problem with the upstairs lighting as it kept tripping rcd removed all lamps and checked all fittings , circuit tested out fine when insulation resistance r1+r2 and Zs but still kept tripping rcd so put circuit on non rcd side of consumer unit would I have to note this as deviation on the test sheet ? And add it in to the 'comments on existing installation ' section any ideas please ?
 
stilllearning said:
Recently changed a consumer unit and had a problem with the upstairs lighting as it kept tripping rcd removed all lamps and checked all fittings , circuit tested out fine when insulation resistance r1+r2 and Zs but still kept tripping rcd so put circuit on non rcd side of consumer unit would I have to note this as deviation on the test sheet ? And add it in to the 'comments on existing installation ' section any ideas please ?
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No you should find and rectify the fault. Upstairs lights and downstairs lights on separate RCDs by any chance?
 
try a forum search on borrowed neutral. this is a classic case. landing light fed with L from downstairs cct.and N from upstairs cct.
 
Iam unable to rectify the fault as the property has been decorated and customer is unwilling to have fault rectified the circuit will have to stay on a Mcb now what are my options do I note it as a departure from bs7671 ?
 
what you have to do is put both lighting circuits onto the same RCD. preferably also on the same MCB.
 
stilllearning said:
Iam unable to rectify the fault as the property has been decorated and customer is unwilling to have fault rectified the circuit will have to stay on a Mcb now what are my options do I note it as a departure from bs7671 ?
Click to expand...

You carry out testing for this before you start the job, not after you have finished it, and agree the fault finding and repair with the customer before starting. If they refuse to have it done then you walk away from the job.

If you leave the lighting circuit without RCD protection then the work you have done does not comply with the regulations, and makes a mockery of the point of installing a new CU. You have identified a potentially dangerous fault which could place the life of anyone working on the installation at risk, you now need to do something about this to make it safe.

If you have not made the customer aware of the possibility of finding such faults and the need to rectify them before starting then you may well have to carry out the repairs at your own cost.
 
I come across this one quite a lot. It's not ideal but if the customer really doesn't want the circuits segregated and you've already changed the board I'd put them both on one RCD and MCB as telectrix said. Not ideal but better than having one circuit not protected by an RCD.
 
kenai36 said:
I come across this one quite a lot. It's not ideal but if the customer really doesn't want the circuits segregated and you've already changed the board I'd put them both on one RCD and MCB as telectrix said. Not ideal but better than having one circuit not protected by an RCD.
Click to expand...

Then it is your fault for changing the board without testing the installation properly beforehand, and you should be fixing it at your own expense.
 
I have this situation in my house.
Whoever installed experienced the same issues with tripping.
He did what Telectrix suggested.

I think I have a non destructive solution, can someone please critique ?
Put both circuits on the RCD side in separate MCBS

At the landing switch, wire it as a one way switch terminate cables.
Same with the hall swicth
Then fit a discreet flush mounted pir to operate the landing light. ?
 
Your profile lists you as an Electrical Apprentice, question is should you be doing this type of work unsupervised? not having a dig but any self respecting Electrician should have tested this installation prior to changing the CU, another question, why the need to change it in the first place, might be a good idea to get access to the trainee section get a bit more help in there, good luck.
 
newtothis said:
I have this situation in my house.
Whoever installed experienced the same issues with tripping.
He did what Telectrix suggested.

I think I have a non destructive solution, can someone please critique ?
Put both circuits on the RCD side in separate MCBS

At the landing switch, wire it as a one way switch terminate cables.
Same with the hall swicth
Then fit a discreet flush mounted pir to operate the landing light. ?
Click to expand...

Definitely don't do that. It's a breach of 314.4, and the EAWR too. And you may kill a fellow spark or hapless DIYer.
 
just by switching off the MCB ( or pulling the fuse) for upstairs lights and seeing if the landing light stayed on would give you a good indication.
 
Didn't think that I "spoke down" to the OP, my advice was clearly the right thing to do, I agree with you that Apprentices learn better by doing, rather than being told how to do things, but I stand by what I said, the OP ought to be supervised when doing this sort of work. And as a Mentor I take objection to being accused of not being nice, if you bothered to check any more of my posts to trainees, you will find out how fair I am, if the OP has taken objection to my post, then I will apologize to him/her, there was no malice intended.
 
Last edited by a moderator:
Experience gained under the supervision of an experienced electrician, not doing it off their own back as and when they feel like it then relying on a forum to help them with the most basic problems.
He hasn't been spoken down to yet, but it could easily be arranged.
 
Last edited by a moderator:
IzzyS said:
Definitely don't do that. It's a breach of 314.4, and the EAWR too. And you may kill a fellow spark or hapless DIYer.
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Thanks for the feedback, I've just read that reg and I think you might of read my post wrong.
I'm saying each in it's own mcb both rcd protected - not ideal when it trips I suppose.
Or maybe I've got it wrong I'm still new to all this :)
 
I've said it before and I'll say it again.
It always comes up on this sort of post that tests should be carried out before changing a CU. Fine. But given that most CU change requests involve a quote beforehand,I'll be b*****d if I'm going to carry out pretty much a full EICR for nothing on a job that I might not even get. OK,there's no harm in carrying out an IR test and a few Zs readings on the quote visit,but that still leaves a host of potential issues that only extensive testing will identify.The alternative,and my approach,is to carry out some basic tests at the quote stage,and include in the quote that full testing will be carried out while the CU is being replaced and that any faults which require rectifying may incur additional cost. It works for us and we quote and get loads of CU changes.
Quite frankly if anyone tells me they carry out full tests likely to find faults such as breaks in cpc continuity,breaks in rfc continuity,borrowed neutrals etc before every CU change I dont believe them.
 
IzzyS said:
I think you'll still have a shared neutral? I don't think your solution didn't mention separating the two circuits - the quickest safe way is to put them both on the same MCB, making them into 1 single circuit.

This guy explains it much better than I can on here.

https://www.youtube.com/watch?v=7C7Tkge5gvQ&noredirect=1
Click to expand...
Thanks very much mate, I understand now. I see you're right. Cheers for posting the video I found it very useful.
 
wirepuller said:
I've said it before and I'll say it again.
It always comes up on this sort of post that tests should be carried out before changing a CU. Fine. But given that most CU change requests involve a quote beforehand,I'll be b*****d if I'm going to carry out pretty much a full EICR for nothing on a job that I might not even get. OK,there's no harm in carrying out an IR test and a few Zs readings on the quote visit,but that still leaves a host of potential issues that only extensive testing will identify.The alternative,and my approach,is to carry out some basic tests at the quote stage,and include in the quote that full testing will be carried out while the CU is being replaced and that any faults which require rectifying may incur additional cost. It works for us and we quote and get loads of CU changes.
Quite frankly if anyone tells me they carry out full tests likely to find faults such as breaks in cpc continuity,breaks in rfc continuity,borrowed neutrals etc before every CU change I dont believe them.
Click to expand...

You don't leave all of the testing until after fitting the new board do you?
I do the dead testing prior to removing the old board, then fit the board, then live testing.
I don't do any testing when quoting for the job but do allow a few hours of fault finding time plus have provision in the terms and conditions that says I will test the installation and not proceed if a major fault exists.
 
davesparks said:
You don't leave all of the testing until after fitting the new board do you?
I do the dead testing prior to removing the old board, then fit the board, then live testing.
I don't do any testing when quoting for the job but do allow a few hours of fault finding time plus have provision in the terms and conditions that says I will test the installation and not proceed if a major fault exists.
Click to expand...

No,like you at least an IR test before removal. Usually RFC tests/R1+R2 during replacement,as the usual rats nest makes these tests much easier once the old boards out the way and you just have the cables. I've only come badly unstuck once,when a seemingly simple CU change uncovered an absolute nightmare. It took two days to complete the change and sort all of the issues...obviously an EICR before hand would have found it out and had I known I would have recommended a full rewire!
I reckon most issues when I do a CU change rarely add more than an hour or two to the job,often a lot less.
 
SparkyAndGeorge said:
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?
Click to expand...
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
 
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 said:
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.
.
Click to expand...

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.
 
baldsparkies said:
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.
Click to expand...
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 said:
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
Click to expand...

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.
 
shanky887614 said:
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
Click to expand...

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.
 
IzzyS said:
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.
Click to expand...

that's why you should knock the main switch off.
 
davesparks said:
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!
Click to expand...

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.
 
IzzyS said:
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.
Click to expand...

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:
 
baldsparkies said:
A competent experienced electrician who falls for this old chestnut would get a slap from me for being a ****.
Click to expand...

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.
 
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.
 
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