Scratching my head lighting fault???

[Ben Burrows]

Hi guys, am new to the forum. My issue is I got called to a friends house as they have an issue with their lights, I arrived and the issue was 1 lighting circuit controlling about 5 lights. I only had some hand tools on me thinking it would just be a hidden rcd or a lamp! I played around a little and the rcd trips with only the line conductor connected to the installation and the neutral and cpc isolated(with or without them connected). I think am having a mind blank as cannot think what would cause this to trip. Tried splitting the lights but is an old cottage and there must be jb's under the floor as am missing feeds at lights/switches?If anyone has come across a similar situation or can shed a little "light" on the situation, it would be gratefully received!!!

 

[ImpededLoop]

My first port of call would be to take a test kit and carry out the sequence of tests on the circuit.

I'd probably then look at breaking down the circuit and testing each half until I found the cause.

 

[Ben Burrows]

That is the plan for tomorrow! Just cannot get my head round why it would trip without the neutral or cpc being connected? And also when everything connected will turn lights on for 1-2 seconds and then trip the rcd?

 

[ImpededLoop]

Disconnecting the cpc at the consumer unit may not actually disconect the cpc if you have shared cpc's from other circuits (2 gang switches etc) or bonding.

 

[Englishman]

Well do what you're planning to do tomorrow, and then report back if you can't find it.

 

[Ben Burrows]

Will do! Will report back!

 

[telectrix]

i'd take a wander lead with me as well as the mft.

 

[snowhead]

the rcd trips with only the line conductor connected to the installation and the neutral and cpc isolated(with or without them connected).

So with the EARTH DISCONNECTED and the LINE STILL connected, there's a fault?
Were there any other people in the house apart from yourself at this time?

 

[Amp David]

Borrowed neutral possible. Is this fault just started

 

[Ben Burrows]

Not the earth, the circuit cpc. There were other people in the house but not in the area of the fault, why do you ask?

 

[Ben Burrows]

Supposedly just started this afternoon, no diy etc happening, the rcd just tripped! It made me wonder if there is some water getting in somewhere as we have had a lot of heavy rain today? That's the only thing that has changed, though have checked all the lights, there are outside lights but are on another circuit and are all working?

 

[telectrix]

no use guessing. test logically---- continuity then IR. then split circuit to narrow it down.

 

[Ben Burrows]

Yes will do, hopefully will be a lot easier with my mft and analysing my test results, didn't think I would need it lol! - typical

 

[davesparks]

NEVER, and I mean NEVER, energise a circuit with the cpc or neutral disconnected.
I would strongly recommend that your friend employs a competent tradesman who understands the basics of electrical safety.

 

[snowhead]

Not the earth, the circuit cpc. There were other people in the house but not in the area of the fault, why do you ask?

See the post above.
He knows why.