Minor Works, Insulation Resistance Testing, and 612.3.3

[Electric Magic]

Hi all

I couldn't find any previous posts on this topic specifically so looking for some advice.

I am adding an external security light for a customer. I am extending the existing downstairs lighting circuit. Normally when testing Insulation Resistance I would test between L-N, L-E, N-E. This particular lighting circuit has thirty six downlights, fifteen of which are in a large extension with a ceiling that is up to 3.6m high. I've got a 2.1m A frame ladder that will enable me to get high enough to take the lamps out but I'm a bit warey of trying to disconnect the fittings without better equipment. As some LED fittings the fittings are also vulnerable to the L-E part of the test I'm concerned about doing it without removing them. Given that it is an existing circuit rather than a new installation can I just connect the live conductors and test between them and earth (as per 612.3.3)? My reading would be yes I can, but I'd be grateful for views from those with a bit more experience than me. Obviously I'll also test the cable I am putting in L-N, L-E, and N-E.

Thanks

 

[HappyHippyDad]

I personally think it would be OK. To remove 36 lamps for the sake of putting up an outside light does seem a bit excessive! However if you do want to have the minor works filled out with something in the L-N IR section then you could take a look at reg 610.4 which states very clearly that you are verifying that the 'addition or alteration complies with the regulation', rather than the whole circuit.

 

[Brightspark2]

Strap L-N together and test to earth...

 

[joehat]

And put lim in the L-N field

I aways wondered though, can you do the R test L-E and N-E rather than connecting L and N together and testing to E?

 

[Richard Burns]

And put lim in the L-N field

I always wondered though, can you do the R test L-E and N-E rather than connecting L and N together and testing to E?

By connecting line and neutral together you are ensuring that there is no potential difference between these conductors so that the equipment does not experience a high voltage, this then avoids any problems with the internal circuitry of a piece of equipment not being able to handle a 500V potential and being damaged.
If you do the individual tests then you are applying a 500V supply to one conductor and the other conductor, whilst it is floating and so has no reference, may be considered to be at 0V and so you would be applying 500V across the internal circuit.

Most items of equipment can handle 500V as part of their design specification, however in general they are not expecting 500V at any time and so may be damaged.