uHeat Banner - Forum Discount Available
This official sponsor may provide discounts for members

Discuss Beware The Borrowed Neutral in the Lighting Forum area at ElectriciansForums.net

P

PAUL M

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:  American Electrical Advice Forum

i had a phone call off my mate today he had done cu change ,dual rcd as per 17th,he said alls fine until i turn on the landing light (2 way switch) and both the rcds keep tripping,turns out he had put up lights and down lights on different rcds as recomended,turns out when the council wired the house 10 years ago(now private)they had borrowed the neutral for the landing light,so he put both circuits on the one rcd and it worked no problem.he has now told the customer she needs a neutral running from down light circuit to landing light and she has agreed to the work.these new boards are gonna cause some headaches.lol:)
 
B

BEN5637

  • Thread Starter Thread Starter
  • #2
Had the exact same problem mate where landing switch was tripping out both rcds after a board change. did the same put them on the same rcd and made a comment on the installation cert, advised cutomer but they declined a quote. def one to watch out for!
 
T

TONY JONES

  • Thread Starter Thread Starter
  • #3
i had a phone call off my mate today he had done cu change ,dual rcd as per 17th,he said alls fine until i turn on the landing light (2 way switch) and both the rcds keep tripping,turns out he had put up lights and down lights on different rcds as recomended,turns out when the council wired the house 10 years ago(now private)they had borrowed the neutral for the landing light,so he put both circuits on the one rcd and it worked no problem.he has now told the customer she needs a neutral running from down light circuit to landing light and she has agreed to the work.these new boards are gonna cause some headaches.lol:)
had similar problem myself so looks like we have to allow in price to change consumer unit an additional cost for fault finding ?
 
P

PAUL M

  • Thread Starter Thread Starter
  • #4
it didnt happen to me as i said it was a good mate of mine but for a short while it did have him scratching his head:D
 
E

EWebster

  • Thread Starter Thread Starter
  • #5
it didnt happen to me as i said it was a good mate of mine but for a short while it did have him scratching his head:D
Done 5 consumer units around my village in the last couple of weeks (60's housing) and 3 had borrowed neutrals. Must have been the done thing in the 60's/70's!!
 
G

Graeme Harrold

  • Thread Starter Thread Starter
  • #6
Thats where taking a little time to test before jumping in and changing the CU. Gives you the bargining power before rather than after the change...........
 
E

ezzzekiel

  • Thread Starter Thread Starter
  • #7
Thats where taking a little time to test before jumping in and changing the CU. Gives you the bargining power before rather than after the change...........


if a jobs worth doing.......
 
E

EWebster

  • Thread Starter Thread Starter
  • #8
Thats where taking a little time to test before jumping in and changing the CU. Gives you the bargining power before rather than after the change...........
Absolutely. I've learned my lesson now, and haul apart the light fittings first. So far it's almost always the live from the common bridged between downstairs and upstairs hall lighting switches.
 
D

Deleted member 9648

  • Thread Starter Thread Starter
  • #9
Thats where taking a little time to test before jumping in and changing the CU. Gives you the bargining power before rather than after the change...........
As I'ts likely to be an insulation test carried out before changing a CU, a borrowed neutral wouldnt show up.And with the usual jungle of out of order neutrals in the N-bar I doubt whether faults like this can reasonably be expected to be found prior to the work being carried out.
When quoting for a CU change we always add the get out clause that any faults not apparent before work starts may need to be rectified at additional cost.
Alan
 
E

EWebster

  • Thread Starter Thread Starter
  • #10
As I'ts likely to be an insulation test carried out before changing a CU, a borrowed neutral wouldnt show up.And with the usual jungle of out of order neutrals in the N-bar I doubt whether faults like this can reasonably be expected to be found prior to the work being carried out.
When quoting for a CU change we always add the get out clause that any faults not apparent before work starts may need to be rectified at additional cost.
Alan
Yup, I've got that on my quotes as well. It's amazing how many people would rather you bodged the job than chase their walls to run a new line :eek:
 

acvc

-
Arms
A while ago I had the situation on a testing job where the upstairs and downstairs lighting circuits had been put into the same mcb.

I took out the L N and E of the upstairs circuit, left the downstairs in. Connected upstairs R1 and R2 for a continuity test. Switched the c/u back on, with only the downstairs circuit with its rcd left on. (I realise the c/u should have been dead at this stage:eek:).

The point is that when doing the R1+R2 at an upstairs ight fitting, it tripped the RCD. I put this down to a neutral being borrowed from the downstairs light circuit. Was this the right assumption to make?
 
So what is the solution? Most people will simply say its been like that for 50yrs why should I change now.

Placing the two circuits on the same RCD will hide the problem, but retain hidden dangers.

Suppose circuit 1 borrows the netral of circuit 2 . Maintenance work starts on circuit 2, let us suppose replacement of a rose with a modern light fitting and circuit 2 is isolated by locking off the relevant MCB. The wires are drawn out of the rose ready for re-wire, one nutral is attached to the light which is wired from circuit 1, the other nutral is connected to the consumer unit nutral. The light in circuit 1 is switched on.

Now obviousley the light does not work. The nutral from the the light becomes live (because it has no return path), while the nutral connected to the CU is still solid. thus we have a live and nutral side by side, both marked nutral, and both waiting for the maintainer to touch them in the belief that the circuit has been isolated!

In my opinion the only safe remady (apart from a re-wire) is to make them a single circuit , both on the same MCB (and of course therefore the same RCB and nutral bar).
 
Last edited:
M

Monkey1984

  • Thread Starter Thread Starter
  • #14
So what is the solution? Most people will simply say its been like that for 50yrs why should I change now.

Placing the two circuits on the same RCD will hide the problem, but retain hidden dangers.

Suppose circuit 1 borrows the netral of circuit 2 . Maintenance work starts on circuit 2, let us suppose replacement of a rose with a modern light fitting and circuit 2 is isolated by locking off the relevant MCB. The wires are drawn out of the rose ready for re-wire, one nutral is attached to the light which is wired from circuit 1, the other nutral is connected to the consumer unit nutral. The light in circuit 1 is switched on.

Now obviousley the light does not work. The nutral from the the light becomes live (because it has no return path), while the nutral connected to the CU is still solid. thus we have a live and nutral side by side, both marked nutral, and both waiting for the maintainer to touch them in the belief that the circuit has been isolated!

In my opinion the only safe remady (apart from a re-wire) is to make them a single circuit , both on the same MCB (and of course therefore the same RCB and nutral bar).
The way I have been told to do it is to put both lighting circuits into 1MCB and note as a departure on certificate and to also label the board to show this has been done.

As you said otherwise your running a risk of an inadvertantly live circuit. being fed from the other side of the board.
 
E

EWebster

  • Thread Starter Thread Starter
  • #15
The way I have been told to do it is to put both lighting circuits into 1MCB and note as a departure on certificate and to also label the board to show this has been done.

As you said otherwise your running a risk of an inadvertantly live circuit. being fed from the other side of the board.
That's interesting. I guess it depends on how many lights you have on the two circuits as well, although it is permissible to run lighting MCBs up to 20A. Not sure I would want to though.

And saying that, it is definitely safer running them off the same MCB, versus two MCBs on the same RCD.
 
M

Monkey1984

  • Thread Starter Thread Starter
  • #16
That's interesting. I guess it depends on how many lights you have on the two circuits as well, although it is permissible to run lighting MCBs up to 20A. Not sure I would want to though.

And saying that, it is definitely safer running them off the same MCB, versus two MCBs on the same RCD.
I wouldn't want to be going upto 20A on lighting. I've not seen above 10A in domestic yet. Maybe just been lucky.

Like you say its definitely safer then leaving them on 2 circuits on the same RCD. but installation cert should be noted and board should be labelled.

Its not ideal but it does solve a problem.
 
That's interesting. I guess it depends on how many lights you have on the two circuits as well, although it is permissible to run lighting MCBs up to 20A. Not sure I would want to though.
Watch the cable size though. 1.0mm T&E if not bunched and not run through insulation etc can safely handle a bit more than 10A (but you can't get MCBs a bit more than 10A!) . That gives you upto 2300 Watts. Its supprising how quickly this figure can be reached with modern downlighters.

I don't have the OSG to hand to look up the limit for 1.5mm T&E, but on houses with this fault its more likely to be 1/044 or 3/026 and I don't know how comparable they are with 1.0mm and 1.5mm.
 
Last edited:

Des 56

-
Arms
Esteemed
99 times out of hundred the borrowed neutral problem exists only where the landing and hall light switches are grouped
It was unfortunately the most common way of wiring lighting in the 60s and 70s and was not given much importance at the time.because it did not impact on rcds because there were few of them
Today it becomes more of a problem
Getting a feed to the landing 2-way in the hall is usuallly the best method,but whatever the solution finding this problem and being surprised by its presence is the thing to avoid
When considering cons unit changes,always check for this situation
Its better to spend a few mninutes checking than getting into all sorts of trouble doing the change blind
Moaning about the borrowed neutral seems pointless because without botch ups mistakes faults and the rest,our work would be less fruitful
 
S

snowiespark

  • Thread Starter Thread Starter
  • #19
done 3 board changes this month sofar, all 3 had a borrowed N, so i fixed by putting in one MCB... none of the clients wanted any more work and were happy for it to be noted on cirt...
 
Des, While we all seem to agree with the analysis of the problem, the danger always existed, its just that it is more detectable with 2 RCDs in use. Furthermore it seems that amongst the community using this forum that we have a concensus on what is a very simple solution.
 
Last edited:
S

sparky1502

  • Thread Starter Thread Starter
  • #21
sorry but why would u broow the neutral wire for the lighting circuit
 
The concept was that you had a live wire from the downstairs lights in the switch in the hall. This would be connectd to the common for the landing light. Then a 2 core (often without cpc) connected to L1 & L2 (although they were not marked as such in those days) to the landing switch, then a single core to the landing light, before "borrowing" the neutral of the upstairs lights.

Why? probably to save on the cost of 3 core between switches, or maybe because it meant that the electricians did not have to carry 3 core cable, or maybe just because that's the way everybody did it! Also in those days everybody had a pendant and there was no concept of changing a light fitting, so I suppose the dangers were not even considered.

What concerns me is what practices we are using today that will be considered dangerous in 50 years time? Maybe putting wire in the wall at all. I can just imagine it " Those idiots back in 2010 used to put cable in the wall. Why didn't they use proper radio switches?"
 
Last edited:
H

hotXbun

  • Thread Starter Thread Starter
  • #23
OK .... so I gather it's probably just me but something I find hard to resolve ...

I don't know about anyone else but I haven't come across a customer who phones me and says, "Hi hotcrossbunny, please, I want one of those new fangled 17th Edition all singing all dancing consumer units that every plumber/carpenter/plasterer/tiler/decorator/roofer/apprentice insists I need .....................and then said customer rejects the idea of replacing the borrowed neutral! :eek:

As I understand it, some interfering busybody comes along (most prob a plumber :)) and tells customer that all is not well .... "I'm sorry to tell you this, but your electrics are not up to date. You need an "update"! Said customer, being mighty impressed, pleads with plumber for guidance and along comes PartP to the rescue ........ No doubt he/she(!?) has a "P" emblazoned on the underpants worn 'Superman' style ..... "Hi! Part P man (don't ask which part) to the rescue! ... What's your problem?" ... Hmmm,

Excuse the digression, but why is it ok as long as everything is 50mm beneath the surface? What is it that the plumber knows and I don't?????...
 

Gravid

-
Arms
"As I understand it, some interfering busybody comes along (most prob a plumber :)) and tells customer that all is not well .... "I'm sorry to tell you this, but your electrics are not up to date. You need an "update"! Said customer, being mighty impressed, pleads with plumber for guidance and along comes PartP to the rescue ........ No doubt he/she(!?) has a "P" emblazoned on the underpants worn 'Superman' style ..... "Hi! Part P man (don't ask which part) to the rescue! ... What's your problem?" ... Hmmm,"

HaHa brilliant, wish I'd got part P underpants instead of a mouse mat.

Maybe they'll stop selling screws and nails longer than 1.5" to anybody who owns a house soon. Who knows why 50mm ? All i know is it says so on page 100 BRB reg 522.6.7, anything less than or not complying with........, needs an RCD.
 
Bulk Workwear - Clothing Suppliers for the Whole Forum Network
This official sponsor may provide discounts for members

Reply to Beware The Borrowed Neutral in the Lighting Forum area at ElectriciansForums.net

Top Bottom