Help IR testing lights with fault which are connected

[Mazza78]

Good evening

I’m after some advice please. We have wired up existing circuit in singles and put in new mcb for lighting circuit. The circuit won’t reset as mcb trips instantly so obviously short circuit somewhere. I’ve read about testing a Live and neutral together to earth at 500v but how am I supposed to test L-N with lights connected that I can’t disconnect or get access too please?

 

[johnb2713]

Good evening

I’m after some advice please. We have wired up existing circuit in singles and put in new mcb for lighting circuit. The circuit won’t reset as mcb trips instantly so obviously short circuit somewhere. I’ve read about testing a Live and neutral together to earth at 500v but how am I supposed to test L-N with lights connected that I can’t disconnect or get access too please?

Disconnect the L and N lighting feed at the Consumer Unit. Join L & N together, megger at 500v between the joined cables and earth. That is what I think youre describing.

 

[Sharpend]

sorry i dont understand when you say you have wired up an existing circuit in singles and put in a new MCB.

are you saying that you have rewired an existing circuit with singles.......
you have changed some fittings on existing circuit which is wired in singles........
And why a new MCB?

 

[SPECIAL LOCATION]

Good evening

I’m after some advice please. We have wired up existing circuit in singles and put in new mcb for lighting circuit. The circuit won’t reset as mcb trips instantly so obviously short circuit somewhere. I’ve read about testing a Live and neutral together to earth at 500v but how am I supposed to test L-N with lights connected that I can’t disconnect or get access too please?

I don't understand how your dead tests prior to energising didn't identify any issues??

 

[Mazza78]

Hi. Sorry should have explained better. We have made alterations to an exsisting lighting circuit wired in singles. Added in extra klix above ceilings and sepearate pirs. Another person has been upgrading the fuse board to new Schneider one.
Client asked for lights on so other lad temporarily turned on and mcb tripped instantly.
So tomorrows job is find the fault. Just wanted to ask how you IR test L-N if there’s potentially lights connected in a room we can access if it’s a potential L-N fault.

 

[ProDave]

Well the obvious place to look for the fault is where the alterations have been made.

As it is an MCB that is tripping you have a L-N short or near short so it is not insulation testing between L and N but continuity testing. That will show up a very low ohm reading and won't be bothered by the higher reading of lights that might still be connected.

Of course there are also possibilities it has been connected wrong in the new CU.

 

[Murdoch]

Are you sure that the neutral is in the correct neutral bar?

and who is “we” ?

 

[Bruspark]

Once more than one person is responsible for a job, no-one is responsible for the job . .

 

[SPECIAL LOCATION]

Client asked for lights on so other lad temporarily turned on and mcb tripped instantly.

I still don't understand why no one has taught to dead test prior to energising any alteration temporary or permanent?
Lets just hope you never just quickly energise a circuit that could endanger a customer!

Methods for IR testing are clearly given in OSG and GN3..
Someone qualified amongst your company should have access to these even if you dont.

 

[Mike P]

As mentioned earlier. There is no need for insulation test. If the trip is going strait out, it’s a short and ordinary dead testing with a multi meter (with lamps in circuit) will locate the problem!

 

[unphased]

Just patiently back track and look at all the new wiring and connections. When you install new stuff and the mcb goes bang it can only be a mistake in the wiring up. You've either put a neutral and live the wrong way about or pinched a cable screwing something to the ceiling. Look at your Klix box for starters!