Tripping out BOTH RCDs

[robsparx]

did a cu change on friday. tt system, simple split load board, dual rcds. Theres a fault on one of the lighting circuits. when one of the light switches is turned on it trips out BOTH rcds on the CU.

going back to the house shortly to further investigate. would this be a borrowed neutral on the lighting circuit?

 

[Mr Mark Sparks]

yes sounds like something is "joining"the 2 rcds together you could prove this by temp putting all the lights on 1 side to see what happens

 

[Spudnik]

Its a borrowed neutral.

Or you have crossed connected them in the CU.

Good luck with finding it

 

[Guest123]

Hi.

Check the landing light as it sounds like a borrowed neutral where the live comes from the downstairs lighting circuit and neutral from the upstairs lighting circuit.

If there is a 2 gang switch in the hallway i.e 1 for hall light and one for landing light you will probably find the commons are linked, with a T+E going upstairs to the landing light switch and a single core going from the landing switch to the landing light. The neutral is then part of the upstairs "loop in" circuit.

With the lighting split over the 2 RCD's this is seen as an imbalance by both RCD's causing them to trip when it is switched on.

Could also be crossed neutral in CU

 

[robsparx]

Its a borrowed neutral.

Or you have crossed connected them in the CU.

Good luck with finding it

thought so. definately not cross connected in the cu. finding it on a sunday afternoon is not my idea of fun

@lenny. you must be psychic lol. its the landing light thats tripping it out. on a 2g switch in the downstairs hall. supposed to be showing the ELECSA assessor this job tomorrow aswell. wil have to get it fixed tonight

 

[Guest123]

Have come across it loads.

It was common practice in ye olden days

 

[Spudnik]

Good Man!!

I have to say tho, in all the CU swaps ive done since 17th, i have never had a problem with borrowed neutrals in that manner before.

Plenty of bodges though.

 

[Had8Lives]

Only solution is to rewire the strapper in three core. Hope it's not a long run.

 

[baldsparkies]

thought so. definately not cross connected in the cu. finding it on a sunday afternoon is not my idea of fun

@lenny. you must be psychic lol. its the landing light thats tripping it out. on a 2g switch in the downstairs hall. supposed to be showing the ELECSA assessor this job tomorrow aswell. wil have to get it fixed tonight

Had the same borrowed neutral on landing light problem with one of my jobs that was being used on an NICEIC visit.
Sorted it prior to visit which was a must because the nic see borrowed neutrals has a code 1.
Probably the same with ELECSA.

 

[robsparx]

still not sorted this. i disconnected the light to stop it tripping out the rcd until i came back, and when i did they said they'd had water come in through the roof and drip through the light overnight. lucky i'd already disconnected it. So i've left it how it is until the roofs sorted.

they dont seem keen on having to have rewiring done though

 

[Guest123]

Hi Rob.

Are there smoke detectors in the house wired on their own circuit back to the CU???

 

[robsparx]

Hi Rob.

Are there smoke detectors in the house wired on their own circuit back to the CU???

hi lenny. no, theres no smoke detectors

 

[Guest123]

Bang goes that way out of it then.

 

[Mac]

Is there water in the cable

 

[pushrod]

I know it's against the idea of a split load CU but would it be a short term fix to put both lights on the same side

 

[tenheads]

defo borrowed neutral common fault now with these bleedin rcd,s no way to sort it other than rewire it

 

[piz]

Hello A bit new to this game but have expirenced this! since then before I change a cu check continuity on all neturals the only ones that have continuity should be the ring main if the lighting circuit has continuity would be easy to tell customer more money to fix the fault
also tell them if you change fuse board will show up faults on old cookers washers etc
Nic say it is ok to leave on same circuit if you make a note in the cert at customers request

 

[andekoch]

Landing lights seem to have this problem when wired in days of old (as mentioned in a previous reply). Sometimes it is easier to run a neutral from the CU to the offending light from the appropriate RCD. First saw this on the CU change I was using for my NIC visit as well.