Lighting issue

[Gr4h4m P4ge]

Has anyone come across this before, client told me all lights were working previous to fuse board change, but when I turn light on in one room to a fitting with lamp in, it trips out RCD, when lamp is removed and light switch is turned on and off RCD stays on, all other light fitting with lamps in on same circuit(4 in total)all work as they should, I have checked insulation resistance , there is 230v between live and neutral when switch on at the lamp holder , then 0v between live and neutral when switch is switched off. This has got me totally stumped, please help

 

[telectrix]

what lamps/bulbs are fitted?

 

[Pete999]

what lamps/bulbs are fitted?

borrowed N,

 

[telectrix]

borrowed N,

could well be. usually on 2 way landing light.

 

[SJD]

Does just one RCD trip, or two?
If two RCDs trip, then expect a borrowed N - the circuit for the light in question, and the circuit the N is borrowed from.
if juts the one RCD trips, perhaps that light is wired across L and E, and thus tripping the RCD when operated. Could be mixed up connections in a ceiling rose, or elsewhere.

 

[Pete999]

Does just one RCD trip, or two?
If two RCDs trip, then expect a borrowed N - the circuit for the light in question, and the circuit the N is borrowed from.
if juts the one RCD trips, perhaps that light is wired across L and E, and thus tripping the RCD when operated. Could be mixed up connections in a ceiling rose, or elsewhere.

JUST after A CU change I believe the OP said

 

[SJD]

JUST after A CU change I believe the OP said

Yes I noted that, not sure why you raise that? Before a CU change with no RCD, a L to E connection would not be noticed, after it would trip the RCD. And testing with no lamp in place, perhaps would not be noticed (or, of course, no testing!).

 

[Gr4h4m P4ge]

what lamps/bulbs are fitted?

only one RCD trips, lamp that I am trying to switch on is a BC lamp, previously it was a GU10 LED lamp

 

[telectrix]

then the borrowed N is favorite. what you could have is a 2 way light with N from the upstairs lighting cct. and L from the downstairs. if up and down lights are on different RCDs then that would cause 1 or both RCDs to trip when the light is switched on with a load connected.

 

[Gr4h4m P4ge]

then the borrowed N is favorite. what you could have is a 2 way light with N from the upstairs lighting cct. and L from the downstairs. if up and down lights are on different RCDs then that would cause 1 or both RCDs to trip when the light is switched on with a load connected.

this is a 1 bed flat, with 4 rooms in total, only 1 lighting circuit, no 2 way lighting anywhere, all other lights can be on, and bedroom light switch can be on with no lamp in place, and all power stays on, as soon as you put a lamp in and switch light on, RCD trips

 

[telectrix]

is the problem lamp wired L-E?

 

[Gr4h4m P4ge]

is the problem lamp wired L-E?

I have put a temporary simple double insulated BC pendant holder, so no E is required

 

[loz2754]

Could be that the fixing screws for the ceiling rose have penetrated one of the cables above the ceiling, creating a fault from neutral to earth, which would only cause the RCD to trip when the lamp is in and switched on.

Or somewhere else along the same part of the circuit.

 

[Gr4h4m P4ge]

Could be that the fixing screws for the ceiling rose have penetrated one of the cables above the ceiling, creating a fault from neutral to earth, which would only cause the RCD to trip when the lamp is in and switched on.

Or somewhere else along the same part of the circuit.

Will have a look, when I am next back at flat, thanks for all scenarios, hopefully one of them will fix fault

 

[GBDamo]

Had one similar on a board change, the outside light had been fed from the back door light switch. With no Neutral at the switch I was scratching my head as to where they had got a Neutral from.

Turns out they had fed a single down the partition wall and into a socket bellow to grab a Neutral.

Ended up disconnecting it and all was well.

This was from an up front RCD board to an all RCBO board and in this situation the only pre testing I do is an RCD test.