Help please with understanding a borrowed neutral

[baza]

Hello everyone
Could someone explain why the following happens with a borrowed neutral?
Did a cu change today and installed a dual rcd board, Previously the up and downstairs lights were on the same mcb. I was half expecting the rcd/s to trip when I separated them, which they did. I dont need help in how to remedy this, but my question is when disconnecting the link at the back of the switch feeding the strappers linked to the other switch, I would have thought that I had removed the inbalance and the rcd would remain on.
Thanks in advance

 

[hasel5]

You a 5www?

 

[telectrix]

in this situation, it's not what i call a borrowed neutral more like a borrowed live, where the L for the landing light comes off the downstairs. by removing the L link, you will lose the landing light, but it should sort the RCDs out, as they only trip when you switch the landing light on. time to do some testing. bet you have a neutral in the wrong bar somewhere.

 

[onions1066]

You a 5www?

Not really helpful reply

 

[derek]

Try drawing a circuit diagram of the scenario you are looking at, it might help to explain it.

 

[Scornio]

Hi Baza,

try putting the two lighting circuits back on same rcd... If it holds in them seems you still have a borrowed neutral.

 

[baza]

Hi Scornio
yes they do hold when I do that. My misunderstanding is by disconnecting the link from down to upstairs I would have thought the imbalance would have been removed or am I thinking wrong

 

[ste77]

Hi Scornio
yes they do hold when I do that. My misunderstanding is by disconnecting the link from down to upstairs I would have thought the imbalance would have been removed or am I thinking wrong

see post 3

 

[Scornio]

Hi Baza,

Your not thinking wrong, I'm just implying that you still have a fault and seems likely to be a borrowed neutral. I would look again closer.

 

[telectrix]

if you have dissed the L from downstairs and it still trips, then, as you say if the lights are on the same RCD and it doesn't, that suggests the problem is still with the lights. could be a DIY job for an outside light where, unable to get a N at a switch, some numpty has borrowed it from the other lighting circuit.

 

[guest119]

Are you actually taking money from people for electrical work?
Not a ribbing by the way, a serious question.
Boydy

 

[baza]

Thanks Telectrix, spot on, I rewired the borrowed live and put a neutral in the right bar, I feel daft missing that one.

 

[Silly Sausage]

Try drawing a circuit diagram of the scenario you are looking at, it might help to explain it.

Sound advice!

Amazing how it clarifies a problem sometimes.

 

[lofty84]

Im not a Electrical Trainee but dont really understand this borrowed neautral business. Its not a good look but can anyone explain to me what is occuring in this instance and maybee give me an example of it, and maybee even how you would put it right.

fingers crossed I dont take to much of a kicking for asking ...

 

[trev]

In a nutshell it's where someone joins the neutral from one circuit onto the neutral of another, often because of laziness or not having a bloody clue

 

[lofty84]

thanks trev. HOw would they do that though as surely any new cable would have a cpc, L, and neautral unless they cut it of then it would be there for them to use.

or do you mean Mr Jones decides to put an outside light at the front of his house right by the front door so he can see where the hole is for his key as he is fed up with it taking 5 mins every night through the winter. Instead of logically taking his feed from the the hall light for example he has decided that he will take it from the outside socket which was installed to power his lownmower when he wants to cut his front lawn because it was a shorter route. therefore when I go in and switch the mcb of for down stairs lights if I wasnt to double check it was dead then I would get a shock because there was still power feeeding it from the outside socket which was on the down stairs ring?

 

[farmerian]

They a clue in the name borrowed neutral, it when a neutral has been connected to a different circult basically, a RCD will only pick this up

 

[derek]

http://www.electriciansforums.net/i...cal-installations/37498-borrowed-neutral.html

I think the above link has a decent explanation. In the example you have given if he took the Line from the lighting circuit and the neutral from the socket (or another lighting circuit on a different circuit breaker) as his return path then it would be a borrowed neutral and so require isolating two circuits to make safe.
The actual example you have given could mean that he is using 1.5mm cable on a 32A breaker- undersized cable/oversized breaker.
You should always - always - always use a voltage indicator (meeting GS38) before working on a circuit.

 

[electric will]

Imagine connecting up a new load but take the live (line) from 1 circuit then take the neutral to another circuit.
So power comes from one circuit but returns via another.
Im not the best at explaining things but that how I see borrowed neutrals.

 

[rickm]

Used to be a acceptable way of wiring before 3core and rcds. Pretty easy to rectify . It trips rcds cos its not a balanced load .ie current is being drawn from 1 side of the split load and returns on the other side of the board. The rcd thinks the current is leaked somewhere

 

[derek]

Although the borrowed neutral may have been common practice I don't think it has ever been acceptable (at least not for 65 years or so), a little research on the IET forum seems to suggest that even the 11th and 12th editions didn't allow it and the 13th edition 1955 definitely didn't allow a borrowed neutral, "The wiring of each final sub-circuit shall be electrically separate from that of every other final sub-circuit".

 

[Flakey]

Borrowed neutral will only become apparant when rcds are installed. Its like crossing neutrals in the board. For example say you have two lighting circuits one on one RCD the other on the other RCD but the neutral of one of the lighting circuits is incorrectly connected to the neutral bar of the other lighting circuit then the RCD wil trip. so its like connect the neutral of one circuit is connected to the neutral bar of another circuit just further down the Circuit!!

 

[lofty84]

Cheers boys I thought it was something like that it doesn't sound right so not to sure why people would do it but I guess I you don't do it you wouldnt really know. Sometimes people say electricians do it because they are lazy but I'm trying to understand how this could be as if your taking a live and cpc from one circuit you migh as well take the Neauteal from there as well so it just sounds like more work to me. Good point about taking a neutral from a ring to feed a light I wouldn't actually do that but it was a silly example none the less. Cheers for the link

 

[VoltzElectrical]

I still can't understand the physical wiring of this borrowed neutral business. As has been stated, if you need a feed from somewhere, just take the neutral from the same source i.e. a ceiling rose. Seems like more work cobbling a feed from two sources.

I don't work in houses so have never personally come across it. I understand the science of why the RCD trips, but TBH I have given up trying to understand the rest.

(i'm going to read that other thread now to see if that helps lol.)

 

[Flakey]

A scenario i could make up is say: you have a one gang light switch that switches a pendent for example all you had in the switch was the switch line and permanant but no neutral. Now say you wanted wall lights that were switched from the same switch location you would need a 2 gang switch but there would be no neutral there may be a socket locally that may be "easier" to access near the switch so borrow a neutral from there. (DONT DO THIS) Example scenario purpose only!!!

 

[derek]

Perhaps the reason for so many borrowed neutrals in the UK is that many DIY 'experts' have been having a go at domestic electrics for many years before (and since) part P came in.

 

[Scornio]

It happens a lot when you have 'loop in' systems that sends the live and switch live to switch say by the front door... Then the average DIY er decides he wants an outside light switched from same location and thinks he'll get the feed from there.
probably wires the cable in as well before realising there is no neutral... Then the inevitable happens.... He either uses the cpc or borrows a neutral from nearest location.

 

[VoltzElectrical]

It all confirms WHY i don't now, or ever want to, work in houses!

Commercial/ Industrial is way easier and more rewarding. WHY does every new member on here want to become a flippering Domestic Installer? I'd clean toilets before doing that! (I have cleaned toilets by the way - straight out of university too I might add! Then i went on to factory work before doing teacher training, but that's another story!)

 

[Ducksy]

I was confused by this maybe these pics will help you understand




free image hosting

 

[VoltzElectrical]

sorry bud. That does not help in the slightest! Hang on, i can hear a beer calling me from the fridge........

 

[Stroppy]

Commercial/ Industrial is way easier and more rewarding. WHY does every new member on here want to become a flippering Domestic Installer?

For some of us (ie: Me) we didn't really have a choice. My first job as an apprentice was with a domestic installer, so that is the route I have found myself stuck in. I say 'stuck' as I have tried to move to commercial/industrial, but having no experience with that side of things (3 phase, singles, cable tray, steel, etc) no-one wants to give me a chance as a 3rd and now 4th year, so I seem to be doomed to be a domestic, which to be frank is a pain in the ar$e, hacking holes in door frames, I want a socket in the middle of that wall but don't damage the wallpaper or axminster carpet, fix my light which I've smashed off and snipped all the cables off in the grade 1 listed ceiling blah blah...

 

[guest119]

Oops, Ive just landed on a Electrical Trainee thread :banghead:

Boydy

 

[electric will]

sorry bud. That does not help in the slightest! Hang on, i can hear a beer calling me from the fridge........

That should help,as that wiring diagram makes it clear, with the lighting circuit your working on isolated, if you disconnect a neural that another circuit is using (borrowing) that disconnected neutral will become live, through a filament in a lamp etc

 

[Knobhead]

For some of us (ie: Me) we didn't really have a choice. My first job as an apprentice was with a domestic installer, so that is the route I have found myself stuck in. I say 'stuck' as I have tried to move to commercial/industrial, but having no experience with that side of things (3 phase, singles, cable tray, steel, etc) no-one wants to give me a chance as a 3rd and now 4th year, so I seem to be doomed to be a domestic, which to be frank is a pain in the ar$e, hacking holes in door frames, I want a socket in the middle of that wall but don't damage the wallpaper or axminster carpet, fix my light which I've smashed off and snipped all the cables off in the grade 1 listed ceiling blah blah...

Now where did you want that socket?

 

[SirKit Breaker]

It was common practice many moons ago. The lighting circuits would be supplied with an individual live to upstairs and downstairs lights, then a neutral would be run around all of them and back to the board, so 2 lives and 1 neutral, each live was then terminated into separate fuses, hey presto 2 lighting circuits. Then someone invented the RCD and updated the regs, and now we have lots of borrowed neutral issues because of this. I once had a DIY charlie job to sort, he had put an outside light up, dug through the outside wall into the kitchen light switch, tapped into the live, and put in his switched live, but the light had no neutral, so he moved the light up the outside wall till it was in line with the socket in the bedroom, dug through the wall and took the neutral from the socket, turned his light on and lost power to half his house, then he rang me.

Cheers...........Howard