How to resolve borrowed neutral on landing/hallway lights

[ringer]

Still learning, and not come across this yet, but I believe this is a fairly common problem, so would appreciate some info on how to resolve the borrowed neutral problem.

I take it when you come across this situation, you need to ensure that both live and neutral on both hall and landing switches and lights are on the same circuit - assuming there is two-way switching involved. Is there a preferred circuit to use (upstairs lights or downstairs lights), or does it not matter which one? Am thinking of inconvenience and safety for the user if one circuit trips.

I assume the installation work to rectify this fault would be the same whichever circuit is chosen. And what typically is required for the installation work - lift landing floor boards then one chase in full height of the landing wall from down circuit to up circuit, containing two lots of T&E?

 

[martysparky]

RCD's need to balance so if the flow is out of one and in another they are not balanced.

 

[Monkey1984]

Depends on what you mean by resolved. A complete resolution is to replace the cable.

However you can install both lighting circuits on the same RCD With a warning note attached and a comment on the EIC or double up both lighting circuits in one MCB so that when work is required on the lighting circuit both are isolated. A warning label must be attached to the CCU stating that borrow Neutrals exist in the installation. If you go for this option.

 

[Amp David]

Without rewiring of some kind, the way round it is to put the circuits on the same RCD/RCBO.

I usually tend to take any stairway/landing lighting from the upstairs circuit.

 

[ringer]

I can see how putting both circuits on the same RCD/RCBO would possibly provide a quick and reasonably inexpensive fix but this would not then comply with regulation 314.1.(iii):

314.1 Every installation shall be divided into circuits, as necessary, to:
...
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
...

 

[ezzzekiel]

but there is no other option (if client refuses additional works) division can still be applied across other circuits - not brilliant but no other way.

lighting should also be moved to same mcb so isolation occurs on the whole circuit, if cables are 1.5mm better to uprate to 10a mcb if using as single circuit for all lighting, also well identified as mentioned earlier.

 

[ringer]

but there is no other option (if client refuses additional works) ....

Ok, I get that. Working in the real world, rather than totally by the (Big Red) book.
As a matter of interest, what sort of cost are we talking to do it properly with lifting, chasing, making good etc? Number of hours will do. I take it the cost of parts (cable) will be minimal.

 

[ezzzekiel]

usually around days labour + materials should cover it

 

[rocker]

Just out of interest, is anybody actually using the borrowed neutral method when doing rewires etc? To me it always just seemed like laziness that was bound to cause confusion, were there any other reasons to do it (can't be cost copper was much cheaper back then)

 

[nickblake]

say the neutrals taken from the first floor and the switching is from the ground floor ,disconnect the supply to the light fitting and put in a junction box ,you may find that the switch wires are in Double insulated singles from the ground floor if this is the case leave it where it is , then run a new double insulated single from the ground floor neutral problem solved , this is fully acceptable way of doing it .,but ensure that the is also an earth present in the fitting if its a class 1 , rocker just done a CDU uprade 1970's house , when doing the R1R2 tests on the ring , the crossed leg test , got some wiard readings on the first floor found that the ring covered two rooms the first floor sockets were taken from the ground floor with radials and daisy chained , round the rooms , thats lazy so the now have a ring on a 20amp mcb

 

[martysparky]

If there is borrowed neutrals it should be rewired coz it just no right as far as I'm concerned. As we all know most shocks are caused by confusion so I would always advise to avoid that.

 

[Risteard]

I can't see how having them on the same RCD to prevent tripping could possibly ever be a solution (irrespective of cost constraints). Borrowed neutrals are extremely dangerous.

Regarding comments about "double insulated" singles (or other cables) - they are not "double insulated". These are insulated and sheathed.

 

[rocker]

Nick I see that sort of thing a hell of a lot round here - all the ex council houses have a ring going upstairs, and all the downstairs sockets are unfused spurs from that ring. I suppose that's just about OK if it ends there, but obviously over time people add to the circuits so you end up with radials coming off spurs, and you can't just downgrade the MCB in this case as it's the whole house coming off one 20a breaker. I have been guilty of splitting the ring in the middle and sticking each leg on a 20a in the past. Not brilliant I know, but it should stop any cabling going into meltdown.

 

[nickblake]

Nick I see that sort of thing a hell of a lot round here - all the ex council houses have a ring going upstairs, and all the downstairs sockets are unfused spurs from that ring. I suppose that's just about OK if it ends there, but obviously over time people add to the circuits so you end up with radials coming off spurs, and you can't just downgrade the MCB in this case as it's the whole house coming off one 20a breaker. I have been guilty of splitting the ring in the middle and sticking each leg on a 20a in the past. Not brilliant I know, but it should stop any cabling going into meltdown.

i agree its the same up here , in this case i was lucky as the kitchen was wire on its own circuit and also the utility was on its own to so i did some load checks and it should be ok on a 20 amp , stuck it on the cert and CDU , the houses on the estate are all the same wired by a hungarian in the early 70 's

 

[nickblake]

I can't see how having them on the same RCD to prevent tripping could possibly ever be a solution (irrespective of cost constraints). Borrowed neutrals are extremely dangerous.

Regarding comments about "double insulated" singles (or other cables) - they are not "double insulated". These are insulated and sheathed.

6181XY Double Insulated Cable 600/1000V BS7889 the cables i was refering to are double insulated

 

[mickytuff]

The borrowed neutral situation on landing/hall light fittings is a very common situation especially where the circuits have been wired in 2 plate (double insulated singles rather than twin an earth) this i mite add is common to properties that were rewired 25 30 years ago, easy solution to rectify if u've got an airing cupboard to drop down into using trunking, plan b is the double the circuits up option, this mite not comply to the regs, but as already said if the client refuses and u've binned their old fuseboard your in lumber then, u've improved the circuit in one respect, it now has r.c.d protection!!