Borrowed neutral discovered when changing CU and discussion on DIY CU change

[rsmck]

My usual disclaimer applies - I'm not a professional electrician..

I recently changed the CU in a family member's home as a bit of a stop gap (they are building an extension later next year and will have the property fully rewired then - but for now they asked if I could replace the traditional rewireable fusebox with a modern CU with RCD protection)

One room (not a hall stairway or anything like that) has two-way switches and the irritating issue of a borrowed neutral. I know the 'proper' solution is to provide a new neutral - but as the property is being rewired in a year or so anyway and there's no easy way to run this in without extensive redecorating it's wasn't a viable option.

I've put both the upstairs and downstairs lighting circuits on the same RCD (again, would rather not, but it means they have light!) and marked the new CU with a note stating that the lounge lighting has multiple means of isolation and the relevant circuit numbers.

Is there anything else I could do to improve this situation that I may have overlooked ?

As an aside, replacing the CU also showed two FCUs which, when fitted initially, appear to have had a screw cut into the insulation of the live cable. Presumably these screw heads have been live for many years and no-one has touched them, but certainly made replacing the CU worthwhile

 

[MDJ]

Re: Borrowed Neutral discovered after changing CU

I'm not a professional electrician..

I recently changed the CU in a family member's home

:shocked: :toetap05: :leaving:

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

:shocked: :toetap05: :leaving:

I was waiting for (although optimistically hoping I wouldn't get) that response

The change has been done safely. I've also rewired my last two homes (and had some very helpful advice from others on here)

Despite not being a professional electrician I do have a good understanding of electrical concepts and *do* own and know how to use testing equipment, and conducted (and recorded the result of) full tests on my own installation mainly for my own reassurance - I appreciate it's not valid as a certificate.

Not all "DIYers" are the same....

Now, any other useful suggestions

 

[ian.settle1]

Re: Borrowed Neutral discovered after changing CU

Hope you have notified the LABC or you are breaking the building regulations:6::detective:

 

[trev]

Re: Borrowed Neutral discovered after changing CU

An expensive way of carrying out a relatively easy fix to that problem mate. Presumably the new CU will continue to be in service after you do the rewire.

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

Hope you have notified the LABC or you are breaking the building regulations

No I'm not. No notification is required in that area.

 

[MDJ]

Re: Borrowed Neutral discovered after changing CU

. I've also rewired my last two homes

Gasp :uhoh2:

 

[snowhead]

Re: Borrowed Neutral discovered after changing CU

Scotland?

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

An expensive way of carrying out a relatively easy fix to that problem mate.

A problem they never knew was there, the main reason for the replacement was that there's a damaged fuseholder and replacements aren't available. Seemed a good time to change it.

Presumably the new CU will continue to be in service after you do the rewire.

I won't be doing the rewire - any new wiring in a new build extension over 8m2 DOES require LABC notification and as they're getting a lot of work done the rewire will be part of that. I expect the electrician may choose to use the CU that's already there.

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

Shared nutural on same RCD or same MCB... Please say the latter....

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

A problem they never knew was there, the main reason for the replacement was that there's a damaged fuseholder and replacements aren't available. Seemed a good time to change it.



I won't be doing the rewire - any new wiring in a new build extension over 8m2 DOES require LABC notification and as they're getting a lot of work done the rewire will be part of that. I expect the electrician may choose to use the CU that's already there.

Depends what kind of job you have done, Ive done jobs in the past where the previous install must have thought 1.0mm cable requires a hole big enough to get two fingers in..

 

[9regnac]

Hope you have notified the LABC or you are breaking the building regulations

No I'm not. No notification is required in that area.

Do u not need to notify labc in Scotland??

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

Depends what kind of job you have done, Ive done jobs in the past where the previous install must have thought 1.0mm cable requires a hole big enough to get two fingers in..

All cable enters from behind so there's no huge holes in the side of the CU

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

All cable enters from behind so there's no huge holes in the side of the CU

Good lad......

 

[kingeri]

Re: Borrowed Neutral discovered after changing CU

When you've done can you come round and perform brain surgery on my wife? I know you're not a qualified brain surgeon, but as long as you do it safely and write down all the results on a bit of paper for piece of mind, it'll be fine.

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

When you've done can you come round and perform brain surgery on my wife? I know you're not a qualified brain surgeon, but as long as you do it safely and write down all the results on a bit of paper for piece of mind, it'll be fine.

But there isnt a brain surgeon forum is there??

 

[Clive P]

Re: Borrowed Neutral discovered after changing CU

Hi,

I probably shouldn' say this, but the poster is in Scotland and it doesn't have to be notified. There is nothing that he is doing that hundreds of others can do there, at least he is asking for advice.

Regards.

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

But there isnt a brain surgeon forum is there??

Nar ive googled it.. Deffo not.. Looks like that one trade that you can ask the professionals what to do..
Surely there should be a more vigorous sign up to this.... :ban:

 

[Dan the spark]

Re: Borrowed Neutral discovered after changing CU

Call me silly, but how could a screw head be live and not blow a fuse?? Surely you had earths at the fcu's??

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

When you've done can you come round and perform brain surgery on my wife? I know you're not a qualified brain surgeon, but as long as you do it safely and write down all the results on a bit of paper for piece of mind, it'll be fine.

No, unless you seriously dislike your wife, I have a feeling that would end quite badly - I have no medical experience nor any desire to learn. That makes it a bit of an unfair analogy...

 

[Dan the spark]

Re: Borrowed Neutral discovered after changing CU

The more I look at this, the more I think this is a wind up!!

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

No, unless you seriously dislike your wife, I have a feeling that would end quite badly - I have no medical experience nor any desire to learn. That makes it a bit of an unfair analogy...

Yeah but you have watched casualty haven't you, What training have you had at being a spark and what experience have you at testing ?

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

Call me silly, but how could a screw head be live and not blow a fuse?? Surely you had earths at the fcu's??

Good question - don't have a good answer for you. All I know is that when that circuit was energised it instantly tripped the RCD.

A bit of investigation narrowed it to only being when those FCUs were switched on, when removing the faceplate, the damaged live conductor was clearly visible. Disconnected at the other end, checked the cable, reterminated the connections (with a sensible length, rather cable being stuffed into all corners of the back box) reconnected and everything works ...

I would have expected it to blow a fuse too, unless of course the earth also wasn't properly terminated previously.

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

Call me silly, but how could a screw head be live and not blow a fuse?? Surely you had earths at the fcu's??

Rubber Screws.. Or :****:

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

Good question - don't have a good answer for you. All I know is that when that circuit was energised it instantly tripped the RCD.

A bit of investigation narrowed it to only being when those FCUs were switched on, when removing the faceplate, the damaged live conductor was clearly visible. Disconnected at the other end, checked the cable, reterminated the connections (with a sensible length, rather cable being stuffed into all corners of the back box) reconnected and everything works ...

I would have expected it to blow a fuse too, unless of course the earth also wasn't properly terminated previously.

Dead Tests... Errrrm lets start with IR (L-E) what was your reading?

 

[Dan the spark]

Re: Borrowed Neutral discovered after changing CU

Rcd would have picked up a damaged neutral, fuse would have picked up live to earth. Seriously mate, I wouldn't be sleeping in any house that u had changed the db let alone rewired........ Wind up!

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

- - - Updated - - -

Rcd would have picked up a damaged neutral, fuse would have picked up live to earth. Seriously mate, I wouldn't be sleeping in any house that u had changed the db let alone rewired........ Wind up!

Now I think that a little harsh.. They guy has said he knows what he is doing and how to test an install... However its took energising the install in order to realise there was a fault..

Or is the OP tester the 99p variety that comes from china in the form of a driver ?

I agree I think somebody could be extracting he urine here.....

 

[MDJ]

Re: Borrowed Neutral discovered after changing CU

I liked the fact he changed the DB but insisted he wouldn't rewire the house and the spark that will rewire it will use his DB lmao, umm okay If you say so.

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

Yeah but you have watched casualty haven't you, What training have you had at being a spark and what experience have you at testing ?

Since you ask - I worked in IT/Telecoms for a long time including data centre management, whilst I didn't wire these myself (obviously) I have a good understanding of the *use* of such electrical installation and the concepts associated with them - e.g. UPS systems, transfer switches, generators etc and monitoring the power usage of such installations. I was also responsible for regular testing of equipment.

Outside of this I work as a theatre lighting technician (In theatre this is often actually referred to as "an electrician" - bit of an unfortunate misnomer) and so again need to understand testing, safe wiring practices (many venues make up their own cables including 3 phase cables) and various other electrical things mainly concentrating on lighting.

In terms of formal training - none, just experience and never being afraid to ask if I'm unsure, and getting someone else to do it if I still don't fully understand the answer.

As far as testing, my current home is the first that I've carried out full IR/Zs testing etc following a full rewire (replacing a 1950s VIR installation)

Note - I do not consider myself an electrician - but am happy to undertake basic electrical work for family (fitting lights, new sockets etc) and adhere to all relevant regulations where practicable (obviously old installations won't comply with everything!) and more extensive ones (like rewiring) for my own home.

As an aside this has been discussed (at length) in previous posts

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

I dont understand if no other work was getting done and they are having professional electricians in to do the rest of the work in few months time why in there right mind they have let this kidda play around with it.. I agree with MDJ.. probs end up paying twice in my opinion..

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

Dead Tests... Errrrm lets start with IR (L-E) what was your reading?

I will freely admit I didn't test every circuit in the existing installation - although I did in my own home *rewire*

It was a quick change done as a favour and for short term.

It's safer than the previous installation (with a damaged fuse cover and exposed live) - I'd be surprised if anyone was to disagree with that :/

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

- - - Updated - - -
Or is the OP tester the 99p variety that comes from china in the form of a driver ?

No, a Fluke 1652... Wouldn't touch those neon screwdrivers with a bargepole

 

[trev]

Re: Borrowed Neutral discovered after changing CU

To be fair Rsmck you can't expect to come on a forum for and populated by electricians and make the claims you have without experiencing a little animosity. You claim to understand what your test gear tells you (and indeed this may be the case) then claim that somehow a blatant insulation resistance fault would have went un noticed until the RCD tripped. You could not have performed the IR tests on these circuits or did not get what the meter was telling you.
I appreciate your willingness to have a go but feel that you're in a lot deeper than you realise which is a dangerous position to be in. I hope I'm wrong for your sake though.

Edit

You posted #31 while I was typing this.

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

Since you ask - I worked in IT/Telecoms for a long time including data centre management, whilst I didn't wire these myself (obviously) I have a good understanding of the *use* of such electrical installation and the concepts associated with them - e.g. UPS systems, transfer switches, generators etc and monitoring the power usage of such installations. I was also responsible for regular testing of equipment.

Outside of this I work as a theatre lighting technician (In theatre this is often actually referred to as "an electrician" - bit of an unfortunate misnomer) and so again need to understand testing, safe wiring practices (many venues make up their own cables including 3 phase cables) and various other electrical things mainly concentrating on lighting.

In terms of formal training - none, just experience and never being afraid to ask if I'm unsure, and getting someone else to do it if I still don't fully understand the answer.

As far as testing, my current home is the first that I've carried out full IR/Zs testing etc following a full rewire (replacing a 1950s VIR installation)

Note - I do not consider myself an electrician - but am happy to undertake basic electrical work for family (fitting lights, new sockets etc) and adhere to all relevant regulations where practicable (obviously old installations won't comply with everything!) and more extensive ones (like rewiring) for my own home.

As an aside this has been discussed (at length) in previous posts

With respect any idiot can make an electrical circuit work.. Thats the easy part. The hardest part is designing the install safety.

Buts its clear as day you arnt up to scratch with your testing otherwise the fault you had would have been apparrant before the system was energised.... What other faults did you find when testing the install? Be interested to here some of your result.

 

[Guest111]

Re: Borrowed Neutral discovered after changing CU

Anybody can within reason carry out the tests as laid down in the big book,understanding what the results tell you now thats another matter.

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

To be fair Rsmck you can't expect to come on a forum for and populated by electricians and make the claims you have without experiencing a little animosity. You claim to understand what your test gear tells you (and indeed this may be the case) then claim that somehow a blatant insulation resistance fault would have went un noticed until the RCD tripped. You could not have performed the IR tests on these circuits or did not get what the meter was telling you.

Thanks for the balanced response - I didn't conduct tests on those circuits before changing over the CU - should I have, yes most probably, but I wouldn't have been able to correct anything as I was pretty limited in what I was there to do in the eyes of the homeowners - change one fuse box for another... silly me thinking it would be a straightforward swap I guess.

I appreciate your willingness to have a go but feel that you're in a lot deeper than you realise which is a dangerous position to be in. I hope I'm wrong for your sake though.

I hope you are too... but it's been two years since I did my own home and we've had no problems, so I'm optimistic I've done it properly. And yes, I did carry out all the relevant testing in that installation.

 

[bigbaddave]

Re: Borrowed Neutral discovered after changing CU

I will freely admit I didn't test every circuit in the existing installation - although I did in my own home *rewire*

It was a quick change done as a favour and for short term.

It's safer than the previous installation (with a damaged fuse cover and exposed live) - I'd be surprised if anyone was to disagree with that :/

Enough said... So no checking whether you have an external earth. No checking the resistance on you ring mains and not checking that the RCD you installed actually does the job you intend to do..

Ive had enough of this one... Im out..

:46:

 

[Dan the spark]

Re: Borrowed Neutral discovered after changing CU

I will freely admit I didn't test every circuit in the existing installation - although I did in my own home *rewire*

It was a quick change done as a favour and for short term.

It's safer than the previous installation (with a damaged fuse cover and exposed live) - I'd be surprised if anyone was to disagree with that :/

It seems that you are falling into the same old rookie/diyer delusion that by 'changing the fuseboard without testing and thinking that if there was a problem then the rcd will find it' thinking that you could well be causing a lot more danger than you are preventing.
i think that if they are getting it retired by a professional in the near future that you should have just left well alone and got someone in that knows what they are doing. Just out of interest what was the make of the old board?

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

Buts its clear as day you arnt up to scratch with your testing otherwise the fault you had would have been apparrant before the system was energised.... What other faults did you find when testing the install? Be interested to here some of your result.

Ok, I'll admit I was wrong in NOT carrying out extensive testing on the dead circuits before energising them (but as those were 'professionally installed' albeit many years ago it foolishly thought it reasonable to assume that there was no *major* faults - guess not)

As for the live cable nicked by a screw it makes no sense to me that it hadn't taken out the fuse before then and I guess that there may have been another fault that was corrected when I reterminated that cable, but there was nothing else apparent at the time. And yes, testing would have revealed it.

 

[trev]

Re: Borrowed Neutral discovered after changing CU

I hope you are too... but it's been two years since I did my own home and we've had no problems, so I'm optimistic I've done it properly. And yes, I did carry out all the relevant testing in that installation.

All I can say to that is a few weeks ago I was in a restaurant carrying out an EICR and found an RFC wired in 1mm T&E with a 40 amp MCB. The restaurantuer said the same thing, It had been that way for a couple of years and worked fine, he even showed me a certificate for the job