Puzzling!

[yellowvanman]

New build, customer (who is builder) supplied light fittings.

With the darker mornings builder asked if I could get the lights working. So made it safe and put it on a 13A plug and plugged into the site board.

Before energising obviously did some testing and noticed that insulation resistance was low (0.45M). Went on to investigate and found that it was 3 light fittings. They were 'on' and each was giving an insulation resistance of about 1.5M - even confirmed that with one of them fully disconnected. Anyway left the lights on temporarily.

Made some inquiries with the manufacturers and they come back that insulation resistance should be at least 2M, but ordinarily should be a lot higher.

Went back this week and re-tested, to identify defective lights for replacement and now the insulation resistance is way up (+100M).

I can only think that there may have been some dampness in the light fittings.

Any other ideas?

 

[Darkwood]

Are you saying you insulation resistance tested the lights themselves???

What were the readings between? L/N L/E or N/E

 

[Badged01]

Im liking the damp idea ......

 

[markc123]

When doing the IR what did you actually do? Did you test the lighting or the ring/radial seen as though you've 'plugged them in' ? And did you make sure all loads were disconnected first before IR ? Could be that Mr.Builder has had a battery drill on charge or an electric drill plugged in somewhere....

Or did you IR the lights themselves? Damp could well be the cause, but it could be a million things also...

 

[Marvo]

If the lights have electronic power supplies/drivers/ballasts there may be built-in surge arrestors which will give low insulation readings.

 

[yellowvanman]

Only energised the lights. When investigating the low insulation I energised to see if any lights were on, and there were 3 on because they were on 2 way switching.

With the lights on insulation resistance was 0.45M with the lights turned off >100M.

Took one light down and insulation resistance between L-E was 1.5M.

Did exactly the same this week and all insulation resistance >100M, even on the light I took down.

- - - Updated - - -

Simple G9 lamps

 

[Badged01]

If nothing has changed since the last time you did the test and everything is now OK (and the tester is functioning OK) only two ways for me:

1) Operator error in doing the testing
2) Some environmental factor (e.g. damp)

 

[Darkwood]

Its a simple error of confusion if your earth was connected in the board and you went L/E then it will show the neutral through the lamp to L as E and N are joint at some point on the DNO side.