Neutral insulation fault strange!

[sonobit]

Hi guys got a IR fault, basically there is a low IR reading on the upstairs sockets Live to neutral nothing strange there, but the rcd will only trip if the lights are switched on. so this is what happens i disconnect the lights and the upstairs sockets work rcd does not trip, then connect the lights still ok then flick any light switch and rcd trips. Disconnect the upstairs socket neutrals and everthing else works fine. Iam going to split the ring to find the fault but why would it affect the lights, is it an earth fault? any ideas guys? cheers i know you will want questions answering so ill do my best.

 

[trev]

What have you done prior to getting this fault? Was it existing and you were called to rectify it or have you done something then got this at the testing stage?

 

[sonobit]

I found it at the testing stage i didnt pick up on it before because its a old empty house and all the power was on when i got there. I first found the fault when i turned of the the power at the main RCD switch, then i went round making sure nothing was live. then it wouldnt switch back on. so i then started testing all the circuits.

 

[trev]

So you were called in because of this? or did you do something and this was a result?
I was thinking a diy borrowed neutral at first causing the problem and the owner thought he had best get someone in who knew what they were doing but I'm guessing the old dreaded borrowed neutral crossed your mind too

 

[sonobit]

I was told nothing just instructed by the estate agents to do a PIR on the property, and had no idea of any faults. its not a split board though there is only one rcd main switch.

 

[trev]

Are they expecting you to put things right and paying you accordingly?

 

[sonobit]

all im doing is putting it in my report but chances are ill get the job of sorting it so im just looking for some ideas in case i do have to go back and sort it.

 

[i=p/u]

work out your circuits and do you r1 and r2 and rn tests on sockets if t&e should be nearly all be same result, then do R1+R2 on lighting circuits.. see if reveals you hidden secret how low is low on IR result. could there be a socket in loft and coming off it for lighting maybe just say 123 here i come gl

 

[pushrod]

I take it the upstairs sockets and lights are not on the same rcd. Is your low IR reading 0 MΩ - doing a continuity test might give you a bit more info, eg a neon or a lamp. suspect a neutral interconnection between the circuits.

 

[sonobit]

All the circuits are on the same rcd, and the reading was 0.9Mohms.

 

[Sintra]

Sounds to me that you have a borrowed neutral from a socket to a light fitting. Try isolating socket circuit and remove socket neutrals from bar in cu and connect in a choc block. Now try your lights to see if they all work. If you find any that don't work then reconnect socket neutrals and recheck lights. If the lights then work you have a borrowed neutral.

 

[telectrix]

but all circuits are on 1 RCD. i suspect there's a fault on a switched live somewhere, only shows up when switches are operated. could be a trapped conductor behind a switch.

 

[Sintra]

Got my appointment booked at specsavers for 1.00pm.

 

[dagrat]

Could also possibly be a neutral/earth fault on the lights as the op suggests that the rdc trips when any switch is operated. It may have no connection to the sockets

 

[pushrod]

but all circuits are on 1 RCD. i suspect there's a fault on a switched live somewhere, only shows up when switches are operated. could be a trapped conductor behind a switch.

Sounds an interesting one especially as

then flick any light switch and rcd trips

Reckon the lighting needs more investigation and checking against the up sockets for continuity and IR. If they are on the same rcd it must be an earth fault.