Dead Short after IR testing

[Spazz]

Just had a call off my electrician (one doing council work)

He did a CU change - on testing he IR tested the lighting circuit (500v DC) and got acceptable readings.
When he energized the circuit - RCD trips. Found a dead short between N and E. Investigating now to locate which run of cable/accessory is providing this dead short now. There are no Low Voltage equipment on lighting so nothing could of been damaged.

Any ideas what could of caused this?

 

[AndyL]

yeah, he didnt really do IR test!!

 

[Spazz]

Just dropped all ceiling roses and the fault cleared.

 

[Spazz]

yeah, he didnt really do IR test!!

100% did an IR Test. When he put the bulb back in it shattered in his hand. All ceiling roses back up and not a clue on what caused it

 

[polo1]

Have to say, I always IR test before a board change - doesn't stop there being problems, but at least you know the problem was already there!

Regards

 

[HandySparks]

There are no Low Voltage equipment on lighting so nothing could of been damaged.

All the lighting equipment is high voltage is it then? :biggrin:

 

[Spazz]

But what we don't understand was when he IR tested between N&E there was no fault >900Mohms = good reading!

When he energized the circuit then the RCD tripped. Did a 2nd IR test and then dead short. - Don't understand this - its like the IR test caused the fault

 

[Silly Sausage]

Deleted. Didn't read thread properly!

 

[1shortcircuit]

Perhaps a Neutral wire got snagged on the earth terminal of a pendant when refitting after carrying out R2/R1R2 tests?

 

[Spazz]

All lamps, lamp holders (ceiling roses), switches are class 2 standard 230v fittings. All switches in on position.

 

[DPG]

All light switches on - maybe the 2-way stairs lighting in the other position? Daz

 

[Spazz]

Might have been a cable snagged after R1+R2 like you said 1shortcircuit

 

[Spazz]

All light switches on - maybe the 2-way stairs lighting in the other position? Daz

No 2 way switching. ground floor flat.

Im going to go with the snagged cable on re installing celing rose

 

[1shortcircuit]

Might have been a cable snagged after R1+R2 like you said 1shortcircuit

It may not even have been visible. I've had it on an MK socket before where there is just enough pressure between a conductor and the protective bar that runs across the back of the socket to cause this issue. Cable fine once repositioned.

I also had it on a light switch. Removed metal switch plate, replaced and the fuse popped (rewireable) It was one of those daft flat plate ones and on closer inspection I noticed that there was not enough room in the back box for the cables AND the switch unit. Replaced for a plastic one and advised client that deeper box was required.

Easily done I guess:thumbsup

 

[AndyL]

Might have been a cable snagged after R1+R2 like you said 1shortcircuit

This is why IR test is done after continuity test, all fittings back in place etc, so if IR test was done correctly it would find any snagged cables