Finding borrowed neutral

[alchemist]

Did a CCU upgrade for a friend and he has a borrowed neutral on the lighting circuits, so at present they are on the same RCD until I resolve that and certify. I get continuity between the neutrals on the two circuits when disconnected from the CCU (and lives disconnected too). Connecting to different RCDs causes tripping when the RCD is on, as I expected.

Can anyone suggest a reliable method of finding where the borrowed neutral is? My guess was the two way lighting on the stairs. What should I be looking for, there are no neutrals at the switches. The lighting circuits are wired from the CCU to the first parts of the circuits using singles.

Is it ok to actually leave it as it is, connected to the same MCB on the same RCD?

Thanks

 

[skipy]

Did you try all the light switches to see if the continuity went away? Making a circuit through lamp

 

[Barx]

If its a house. Chances are it's the landing light. There isn't really any other reason to borrow a neutral anywhere else in the house. In this situation the landing light is normally fed at the bottom with strappers going upstairs and the switch from top sitch to fitting, but the neutral will come off upstairs lights. First thing I normally check is how many neutral conductors are in the landing fitting. If it's >1 then chances are it's borrowed. If their is only 1 there, then it's into the loft to see where it comes from. To rectify, run a single neutral from either a downstairs fitting (usually easiest) or the down lights circuit in CU. Take it in trunking inside airing cupboard (or other similar route and connect into landing fitting. The existing neutrals in the landing fitting need to be 'lost'. I normally re-run from previous point to next point cutting out the landing. Suppose they could be crimped in the fitting if access is problem.

 

[skipy]

Yes stairs hall landing are favourite but have had a borrowed neutral on an outside light

---------- Post Auto-Merged at 19:30 ---------- Previous post was made at 19:27 ----------

Found a good check is to have all light off the light that trips the RCD is the problem

 

[alchemist]

Thanks for the advice.

Is another option to take live from the upstairs fitting to the switch, then have the existing strappers to make the switch downstairs work. The downstairs feed can be disconnected from the switch, leaving just the strappers.

That would fix it without running a new neutral to the upstairs fitting? If the switch upstairs uses conduit it could be quite an easy option.

 

[sanny]

if they stay on in seperate breakers with the landing light OFF and trip when the landing light is switched on then that is your problem

 

[steptoe]

Thanks for the advice. Is another option to take live from the upstairs fitting to the switch, then have the existing strappers to make the switch downstairs work. The downstairs feed can be disconnected from the switch, leaving just the strappers.

That would fix it without running a new neutral to the upstairs fitting? If the switch upstairs uses conduit it could be quite an easy option.

it may well be normal type T&E strappers, not 3c&e,

 

[Evans Electric]

Another way , if its nice and easy, is to replace the feed to the downstairs 2way sw with a feed from the upstairs circuit.

 

[ADS]

Did a CCU upgrade for a friend and he has a borrowed neutral on the lighting circuits, so at present they are on the same RCD until I resolve that and certify. I get continuity between the neutrals on the two circuits when disconnected from the CCU (and lives disconnected too). Connecting to different RCDs causes tripping when the RCD is on, as I expected.Can anyone suggest a reliable method of finding where the borrowed neutral is? My guess was the two way lighting on the stairs. What should I be looking for, there are no neutrals at the switches. The lighting circuits are wired from the CCU to the first parts of the circuits using singles.

Is it ok to actually leave it as it is, connected to the same MCB on the same RCD?

Thanks

I don't understand this bit.

---------- Post Auto-Merged at 01:15 ---------- Previous post was made at 01:05 ----------

It's alright - got it now - a couple of switches closed with lamps in place......thought I was going mad

 

[Evans Electric]

One light has "borrowed" a neutral from the other circuit.

 

[ADS]

One light has "borrowed" a neutral from the other circuit.

Yes, Deke, but under normal circumstances that wouldn't give continuity between the two neutrals - the two circuits are using the one neutral.

But it is possible with the circumstances that I added to my post above.

 

[ianmacd]

One light has "borrowed" a neutral from the other circuit.

I would argue that its the live that has been "borrowed" in most situations not the neutral though.

 

[Theorysparky]

Well something is borrowed !!!!!!

 

[Evans Electric]

If you have disconnected both neutrals at the board and there is continuity between them , then they are joined together somewhere .

The same as if you didn't disconnect them , meggered between them elsewhere , there would be continuity because they are both stuffed in the neutral bar.

 

[Charles Wood]

?

 

[sparkytim]

Simple way to find which light has a borrowed N ;

Turn ALL lights on  Switch OFF MCBs and remove 1 Nuetral from bar and put into a connector, turn both MCBs On one at a time and See which lights are on or off.

Do the same with the OTHER N and it will identify an Odd light i.e. landing light.

 

[binky]

like that one Tim, should be nice and quick.

 

[Adrian]

I think we are getting confused here, he hasn't got a borrowed neutral they are linked together somewhere. chances are he has two circuits in a switch somewhere and the neutrals are connected together there 

 

[steptoe]

Did a CCU upgrade for a friend and he has a borrowed neutral on the lighting circuits, so at present they are on the same RCD until I resolve that and certify. I get continuity between the neutrals on the two circuits when disconnected from the CCU (and lives disconnected too). Connecting to different RCDs causes tripping when the RCD is on, as I expected.

Can anyone suggest a reliable method of finding where the borrowed neutral is? My guess was the two way lighting on the stairs. What should I be looking for, there are no neutrals at the switches. The lighting circuits are wired from the CCU to the first parts of the circuits using singles.

Is it ok to actually leave it as it is, connected to the same MCB on the same RCD?

Thanks

I think we are getting confused here, he hasn't got a borrowed neutral they are linked together somewhere. chances are he has two circuits in a switch somewhere and the neutrals are connected together there 

more likely a borrowed neutral in this instance.

landing lights with 2core strappers wired during 15th are very common for this.

 

[Doc Hudson]

I think it will be best to close this thread as the original question was posted in March 2011 and the OP who asked the question hasn't been back on the forum since May 2013.  Up until a new member posted a "?" comment today the previous input was all in 2011.

?

I am going to assume the OP has had the information they need, most information has already been covered. if anyone wants to discuss this topic further it's probably best to start a new thread where any new input will be from current members. Any valid reason to keep it open that I have missed please PM me or another Mod and we will re-open it Thanks.

Doc H.