Insulation Resistance Test With Lamps In (PICS)

[Lectrician]

I have mentioned this before with regards some thread somewhere.....

If you carryout a PIR and state a limitation to INS RES testing from L to E and N to E only (as in not between L and N due to lamp removal etc), you may be surprised with the readings you get.

I did a site with loads of chandelliers with BC candle lamps, it was impracticle to remove lamps, so a limitation was noted. The INS RES was pretty much flat down. It turned out to be the lamps......

This is a pic of a typical BC metal (earthed) lamp holder (not form the site mentioned above).

This is the reading of the lamp. It was originally around 2M, but increased as I tested. I have seen far lower!

This is the reading of an identical lamp from a similar fitting.

So, if you decide not to remove lamps and not test L to N, if you get some low readings, check the lamp bulbs!

 

[Adam_151]

Thats interesting, not seen that before... bad batch of lamps?

If you carryout a PIR and state a limitation to INS RES testing from L to E and N to E only (as in not between L and N due to lamp removal etc)

As we are having an educational thread , I'll point out that testing like that on a PIR could lead to misfortune...when youhave a lighting circuit with sensitive fittings on (or any circuit with sesnitive equipment) then its inadviseable to carry out separate insulation tests between live and earth and neutral to earth, and instead both should be linked together and tested to earth as one test, the former has the potential to apply 500v between live and neutral if the circuit has a fault.




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[skenk]

Well obviously you test at 250v first to make sure nothing is still connected.

What is a 'sensitive' light fitting!? surely it's always preferable to do separate tests once all equipment, neons, transformers etc have been disconnected?

 

[Risteard]

Why were you testing at 1,000V d.c. instead of 500V d.c.?

 

[Lectrician]

It is always preferable to carry out a full ins res test, but this can sometimes be un-economic or just extreamly difficult due to access.

For example - a house full of SELV downlights, a row of fluorescent battens, a chandallier with 40 lamps above a stairwell, a row of outside lighting columns, sign lighting etc etc.

Limitations to a standard house would be classed as lazy TBH.

I have seen this across sites and over a few years - it is not dodgy lamps as far as I am concerned, but it appears every so often you come across lamps which will cause this. The chandallier I referred to had loads of lamps in it that caused this issue.

 

[Lectrician]

Why were you testing at 1,000V d.c. instead of 500V d.c.?

For the purposes of the test, yep.