SOLVED: Suspected borrowed neutral

[Iggifer]

Recently had a bathroom installed in my parents house by a a well known company that begins with a W. All went well except for the install of the downlights in the bathroom.

Board is an MEM 2000 Split Load 16th Ed. and when they moved the upstairs LTG to the RCD would pop constantly, moved both LTG circuits to the RCD and no popping, leading them to suspect a borrowed neutral. No further investigation was carried out.

I have done some investigation and am unsure if they are correct as a borrowed neutral is not something I have come across before. (I'm only partly qualified/in training).

Each MCB in the C/U has two cables and the previous sparks have identified 4 neutrals to go with it. It seems one T+E from the downstairs MCB simply supplies the under stairs cupboard so this is easy enough to identify and exclude from the problem.

This leaves me with 2 x T+E (1 per LTG circuit) and then two singles+earth. One is a N+E and one is a L+E.

Hallway Rose

Contains 2 L+E, 2 N+E and 1 T+E

Hallway Switch

You tell me! However all T+E with twin cores other than the single marked with sharpie. Hallway switch is the rightmost of 3 and landing is the centre.

Landing Switch

One T+E and one single

Landing Rose

Both singles

LTG Feeds

Original sparks grouped both T+E and one single but not the other single, Neutral+E is separate, L+E is taped with the other two.


Reason for the query is board will soon be changed for a Eeaton all RCBO board and will need to resolve this before the LTGs go on two RCHBO's.

I'm thinking the first port of call is to trace that single N, thinking temp link to earth in the C/U and then Megger N-E in roses until I find it, as both roses have singles.

If it does turn out to be a borrowed neutral, what is the best way to resolve this, I do not want to go down the both circuits on one RCBO route, as this is one of the reasons for going to RCBO's, I do not want the parents plunged into darkness in the event of an RCD fault.

If you need any more information I will try my best to answer your questions, and yes, I have a 2330/2391 NICEIC friend doing the C/U change

 

[RF Lighting]

What does the left hand switch do?

It certainly looks like a classic hall / landing borrowed neutral type situation.

 

[Iggifer]

Sorry yea I should have said, this is for a couple of outside lights, which is only controlled by this switch.

I was under the impression borrowed neutrals fell out of practice at the latest in the 80's if not before? The house was fully rewired in 1998, which, from what I have seen, seems to have been a good job, it's all the cowboys that have been employed to do work since that have done bad jobs.

Unfortunately there is a semi-loft conversion (tongue and groove then carpeted) so even if I could pull a new cable through up into the loft, access to the switch drop / rose is going to be very limited.

Any advice that doesn't involve channelling walls? :/

 

[RF Lighting]

Are these lights fed off the downstairs lighting circuit?

The first company I worked for were still rewiring houses with borrowed neutrals in about 1998

My advice would be to put both lighting circuits on the same RCD.

 

[Iggifer]

The hallway is off the downstairs circuit and the landing is off the upstairs circuits - or at least the Lives are.

The whole reasoning behind splitting the two circuits onto RCBO's was as to not plunge the house into darkness in the event of an RCD fault. I know you can use plug in lamps but when the house was rewired the 'rents had the 5a round pin light sockets installed - so all table lamps in the house are on the lighting circuit anyway (I disconnected all these lamps before checking for RCD trippage)

If I have to use a Jigsaw and cut a hole in the tongue and groove to drop a new cable in, then I will do.

I would obviously also like to remove the danger aspects of the borrowed neutral as well as splitting them.

Do you reckon it's worth trying to trace which circuit that single Neutral in the c/u is for? The assumption thus far has been that each circuit has two lives and two neutrals (both by me and the bathroom fitter sparks), however if that single N is on the downstairs circuit for whatever reason and it should be 3N D/S & 1N U/S this would cause the RCD to trip if two were connected on the RCD side, correct?

Thanks for the advice thus far

 

[EFLImpudence]

Why are there so many neutrals in the hall light rose?

Anyone?

 

[Iggifer]

Why are there so many neutrals in the hall light rose?

Anyone?

This is why I'm thinking the single N+E is actually on the D/S circuit - god knows why so many Neutrals though, I did raise my eyebrows when I took the cover off

Is this a dead give away of a borrowed Neutral?

 

[EFLImpudence]

Well, if the landing rose neutral IS on the upstairs cicuit then there is also an extra neutral in the hall rose.

However, if the landing rose neutral IS the extra neutral in the hall rose then it may not be a borrowed neutral (at least not here).

May help ???


Edit - I have made a mistake in thinking the two roses pictured come on together - of course they don't - but I will leave the diagram as it may help you think of something.

 

[ban-all-sheds]

Recently had a bathroom installed in my parents house by a a well known company that begins with a W.

 

[EFLImpudence]

Try this one.

Another extra neutral, though.

Untitled

• EFLImpudence
• 7 Feb 2012
• 1

 

[Iggifer]

Recently had a bathroom installed in my parents house by a a well known company that begins with a W.

Spitting image! No, I kid. Other than the sparks, they did a really good job. The sparks left a feed for underfloor heating/shower pump in the airing cupboard live with the end taped up for a week. Didnt warn anyone it was lie either.

EFLImpudence - thank you for all your help, I guess my next step is to identify those 3 N's in the hallway rose.

 

[ericmark]

Since I can see one link wire I will guess you have the two wire strappers for the up and down stairs two way switch which does equate to a borrowed neutral.

Years ago it was common to instead of running three wires (Plus earth) between the switches to just run 2.

the two way switch arrangement shown has a line wire shown as brown here which takes the line supply to both switches by linking the line from another switch in the switch block one can get away without the third cable.

However this results in a induction loop being created which can put mains hum on radios etc. As a result the practice was discontinued.

However it works OK (except for hum) as long as the two switches are supplied from the same MCB. However as people started to put up fancy lights the load exceeded the 5 to 6 amp that the ceiling roses are rated at so the common practice was to split the two supplies. Although really a borrowed line it is technically know as borrowed neutral.

However before the RCD likely no one was aware that the situation existed. So now you have two ways to get around the problem.

1) Run a new cable between the 2 two way switches with three cores and earth.
2) Return to using a single MCB for all lights.

The latter will likely still produce a mains hum when switched in one configuration and will also mean all lights are on same MCB. But today with energy saving lamps the lighting load has been reduced so likely there is not problem.

However having the lights and sockets for any room on the same RCD means should a RCD trip both table lamps (plugged in) and ceiling lamps could fail together which could according to house design produce a danger. This is down to a risk assessment but could mean you need some emergency lighting is key areas. Or run the lights of it's own RCBO so they will not trip with the sockets so in problem areas table or standard lights can provide light from an alternative source.

These problems should have been fixed by who ever fitted the consumer unit.

 

[Iggifer]

These problems should have been fixed by who ever fitted the consumer unit.

The c/u was fitted by the people that rewired the house and therefore created the problem!

 

[ericmark]

Without testing I am of course only guessing. However it would seem strange to install a consumer unit during a re-wire and also split the lights and borrow a line feed.

Much would depend how long ago. Trying to prove some one got it wrong is hard as often there were years ago no as built plans and so hard to show who got it wrong.

Something seems wrong as RCD's were only fitted to all circuits (except for my house) around 2008 but wiring colours changed around 2004 so the wiring colours don't match the consumer unit type.

I would think it was late 60's early 70's when we stopped using a line off another switch so we could get away with two core cable.

Since we should get the electrics checked every 10 years or less to go back 10 years is about the maximum and I am sure BS7671:2001 did not allow us to run supply and return cables on different routes.

The problem with the regulations is it does not say you can't borrow a line wire it has phrases like 413.3.5 For separated circuits the use of separate wiring systems is recommended. So to work out which bits say you should not do it would take some heavy reading.

 

[Iggifer]

Thanks for the response. To clarify, its a 16th ed split load 1 RCD (6 ways) / 5 unprotected ways.

The install has not been tested since the rewire in 98, and this was only brought to light when the bathroom guys moved the U/S lights over to the RCD side of the board to comply with the 17th.

I'll get the megger on it in the next couple of days, pretty confident re: testing of the rose wiring, however what am I looking for in the switch?