borrowed neutals

underpar12 · Jul 16, 2011

hi
i think i might have a borrowed neutral on the up /and down lighting circuits,can someone explain why this might happen.and how to solve the problem, going back monday morning to sort out. i have double checked the the c/unit neutrals our in the correct neutral bar. is my only option to put on the same m,c,b, and note on cert.

Hawk81 · Jul 16, 2011

The line probably comes from the downstairs circuit and the neutral from the upstairs circuit. Best option is to take a neutral from downstairs to the upstairs light that has its line feed from downstairs. Also sompletely remove the neutral that was going to this light previously.

ezzzekiel · Jul 16, 2011

was a older method of wiring two way switching which will cause a imbalance in modern rcd protected consumer units causing them to trip, a quick fix is to double up all lighting on the mcb, this is not ideal and depends on how much load is placed on the single mcb.
Ideally run a neutral/ earth in from downstairs circuit to landing light or replace with 3 core method between switches.

LlandrilloSpark · Jul 16, 2011

We have maybe all encountered this on two way lighting on the landing/stairs it happens when the light on the upstairs landing takes it's feed from the downstairs circuit, which goes to the switch at the bottom of the stairs and Also to the switch on the landing via the strappers in the multicore cable, because no neutral is run it is borrowed from the upstairs circuit sometimes via a JB in the loft, solution is to run a double insulated single neutral from the landing light to the nearest neutral point on the downstairs lighting circuit, usually via maybe an upstairs airing cupboard then thru the floor to a ceiling Rose for downstairs, I'm sure other guys have different ways maybeHope this helps

underpar12 · Jul 16, 2011

sorry but is the landing light being supplied by the downstairs circuit.and is this because the circuit is switched feed, sorry struggling to get my head around this one.
do you think in future a easy check would be check the two way switching for a three core.

Sickmick · Jul 16, 2011

Yes the landing light wil have the upstairs circuit looped in, which is where the neutral is from, but the live feed will be from the switch in the hall on the downstairs circuit. Borrowed neutrals is a bit of a confusing term as it sounds like a temporary thing, try to think of it as crossed neutrals.

LlandrilloSpark · Jul 16, 2011

Yep supplied by the switch from downstairs, as eez says the Rcd trips because whatever current is being used by the landing light is not returning thru the downstairs circuit neutral thus tripping the Rcd, putting it on the same MCB would IMO be a temporary measure to get u thru the night......when it's winter and u energise the new board and it trips!