Insulation resistance testing on sensitive equipment

[schoe]

When doing an insulation resistance test on selv spots what's the best way to do it without disconnecting all the transformers?

Can you do a complete consumer unit insulation resistance test by linking the live and neutral bars together and testing between earth on a 500 volt test or should it be 250 volts?

I assume in the paper work it goes down as a limitation?

Oh and last one on the schedule of test results for the niceic domestic installer the test results for insulation resistance says test,

L-l,
L-n
E-n
L-e

What does live to live mean?

Thanks chris

 

[Richard Burns]

Test between Line and neutral connected together and earth with the light switch off. Not really a limitation but may want to note what you did on the certificate.

At 230V supply the test should always be at 500V no matter how you do the test (although you might want to try at 250V first to ensure there is nothing damageable still inadvertently connected)

Line line is for 3 phase supplies I would think when doing IR on each conductor separately.

 

[spark 68]

Test between Line and neutral connected together and earth with the light switch off

Why with the light switch off ?, if you are testing with the L+N connected together anyway.

 

[Richard Burns]

Because it is possible that applying 500V to the transformer may damage it even when applying the voltage from live conductors to earth, depending on the electronics in the transformer. Turning off the switch prevents a 500V PD between Line and earth in the transformer.

 

[spark 68]

I just thought I would ask, because most of these transformers, the electronic ballast type are class 2 usually (although not always), and I thought the IR test was to take in the feed to the 230V supply side of things, as I always provide the CPC connected at every point (the JB) whether they are class 2 types or not, as per the regs.

Forgot to add, I usually test at 250V first in this situation (sensitive equipment in general), just to see if anything is likely to break.

 

[Richard Burns]

Spark 68, I think I may be wrong about the damage, just trying to remember and I have now bothered to get the books out (on a Friday night!). I have found the requirement where current using equipment cannot be disconnected for the switch to be open (but I think this is mainly thinking about lamps and fridges and stuff) and the advice that further precautions may be necessary to prevent damage to some electronic devices even when L+N to E is used. I think I remember something about smoothing circuits having connections to earth, though as you say the transformers are usually class II. So not definite about the possible damage may be the wrong sort of electronic equipment to suffer damage.
However L+N to E safest easy test.

 

[spark 68]

Hi Richard,
Some vunerable equipment (certain SMPS/Inverters) do have Line Filter Capacitors fitted, both across the lines and from Line to Earth, so as you say in different circumstances, we either have to disconnect, or it is valid (in some circumstances) to IR test at 250V.

Agreed on most domestic it is easier to connect L+N and test at 500V, although on new installs (single phase) I usually test L to N, and L to E and N to E, before the vunerable equipment is connected, Sometimes in two or more parts (the cable run before and after) where the switch has a neon etc. or between cable runs for Flossies etc. (after the plasterer has been!), and then test again (L+N) after connection

On additions (or PIR's) I just connect L+N.

Cheers,
Spark68