fault!

[paul b b]

hello gents,

changed a cu today and when i switched the second rcd on it triped the first.

I took out the lives one by one and found the fault to be on the upstairs lights, time ran out and had no time to investigate.

any ideas what it might be?

thanks

 

[batty]

More info needed did you do an insulation test if it was clear maybe interconnected circuit up an down.

Batty

 

[paul b b]

did all tests, everything was ok.

what do u mean bu an "interconnected circuit up an down"?

 

[sellers]

i think he means borrowed neutrals etc

 

[batty]

I did a cu change a while back. House was built in 60's to save cable upstairs landing light was fed from downstairs lighting but neutral was on upstairs lighting so I ended up having to use MCB's instead of RCBO's as circuit was interlinked.

Batty

 

[paul b b]

ok i have mcb's but it still trips the rcd!

there is a light in the hall and landing that have two way switching.

how is the quickest way of findine out if this is the problem? wanderlead?

thanks

 

[Tooold]

Put both circuits on the same side, if the rcd dont trip its a borrowed neutral more than likley. Then if it is you can make one circuit or find where neutral is linked remove and put a new cable in to transfer the neutral upstairs. Could be a lot of work make sure customer is aware.

 

[paul b b]

any easy testing to find the netral? or is it just a case of taking everything apart?

thanks as always chaps!

 

[Robin Spark]

Are you going back in morning Paul?

What state did you leave lighting ccts? Did you put both up and down on one side of board or has customer now not got any upstairs lights?

When you return check to see if landing light causes rcd to trip when switched on. Easiest way to start this is presuming you have left mcb off for upstairs lights and you go back tomorrow then turn this mcb back on and if rcd trips then turn off on of the switches for landing light.

Go back to CU and turn rcd and mcb back on. All should now stay on....until that is you try to turn landing light on and everything will go off as rcd will trip but the mcb wont.

Other way to confirm this will be to safely isolate consumer unit, then keeping lamps in and landing light switch in the on position, you then check for continuity between downstairs line and upstairs neutral conductor at the consumer unit.

This will indicate borrowed/neutral from the upstairs light cct and Line supply from downstairs lights.

dependant on the way

 

[paul b b]

thinking back i think the rcd triped before the mcb was on, but maybe wrong.

i have safely disconected the upstairs lights via pulling out the cable and put them into chock box.

am going back monday as i'm away customer is away anyway

 

[betty swollocks]

borrowed neutral for sure

seen this countless times, dont spend a lifetime on this, offer to correct the problem, give them a price, tell them whats involved, then tell them you could put them both on the same rcd/mcb for nothing, they will go for this option and you record this on the cert and cu.... neither meet current guidelines/regs but you can only do what you can do

 

[paul b b]

ok thanks chaps!

lucky they are away as im working in the smoke tomorrow.

mabey i will have a day fault finding for a good price as i could do with the practice!

thanks again

 

[paul b b]

actually can i just clarify,

what exatcly has someone done here? taken a cable from the downstairs rose to the upstairs?

 

[Robin Spark]

Hall light fed from downstairs cct and switched using 2gang switch.

At switch commons will have link wire so as to feed landing light.

Just wondering where is Consumer unit? Is it near or in hallway? and whats above ie bedroom with carpet ?

Ps whats working in the smoke? is it a good old fashioned pub where the beers 80p a pint and you were allowed to enjoy yourself

 

[paul b b]

in kitchen, not easy acsess as there is a built in sink directly above, can just get my hand to a few cables.

can i separate the netrals?

 

[sellers]

basically, what you have is the 2way switch that is in the downstairs hall which is the feed, which goes to the upstairs landing 2 way switch which then goes to the landing light, but the neutral for this light is taken from the upstairs lighting circuit. Thus a borrowed neutral.

 

[paul b b]

ahhh many thanks sellers!

a jargon free explanation, just what i needed after a hard day.

many thanks all

 

[Robin Spark]

No was thinking that if CU was typical ceiling hieght in hall and access above was also easy then you could remove loop in cables from rose, crimp and enclose in choc box and then run a new cable to rose supplied from upstairs light mcb. Switch wires would stay in their original place and you wouldnt have any chasing out to do.

Let us all know how you get on, but think you'll have to leave both ccts on same side of board.

Erm... also just thought are you sure you have got the neutrals on correct side in the first place when you changed CU?

 

[batty]

Could be a borrowed live old sparks used to do some weird wiring.

Batty

 

[Nicky Tesla]

just lift a convenient floorboard to find any ceiling rose below from the down lts cct, and trunk inside a cupboard or somewhere to bring a neutral single into the loft space to the landing light. Take out the other neutrals in the rose or put them in the normally live loop terminal. No need to get a cable to the DB