SELV testng

[Mark.W]

Hi Chaps

I know this has been covered a few times and I have read all the posts, but for some reason the more I read the more confused I am getting! GRRR

Could someone please explain to me in Laymans terms how to test a SELV circuit, I mean break it down to the bare minumum. IE where you put your test probes etc. I need to visualize this in order to get it!!!

I have GN3 but it isn't very clear.

Cheers
Mark

 

[topquark]

You can either remove the SELV or test at 250V when IR testing it, other than that it's the same as any other IR testing. The difference is in the allowable results. What is it you are finding confusing?

 

[Mark.W]

Hi mate

When testing at 250V do you test on the primary side ie. throught the transformer or do you disconnect the secondary side and test from there?

 

[topquark]

You are testing the whole circuit from the CU through so effectively on the primary side. Remember it's the circuit you are testing in it's entirety not just the piece of SELV equipment itself. The only reason for the reduced voltage being used (or testing L+N to Earth) is to avoid damaging the transformer. As long as the resistances are all greater than 0.5M Ohm then it's a pass (investigate anything with less than 2M Ohm).

The alternative is to remove the SELV and test at 500V; but then you are not testing the terminations on the SELV equipment in the same way as the lower voltage method.

 

[Mark.W]

Ok that clears it up a bit! Thanks you're a gent!

So the test is done at 250V from the CU throught the transformer with a min of 0.5M ohm anything less than 5M ohms to be investigated.

What about the additional test of testing for seperation?!

 

[topquark]

The additional separation test is done at 500V (with the same acceptable results as any other test at 500V).

 

[topquark]

Brain reset, those values were for 16th edition (I have edited them). You are correct to say 0.5M Ohms, sorry if I'd confused you with that.

Thanks to Malcolm for pointing it out

 

[James Sutton]

Hi

All I install a lot of AC Condenser units etc and there full of PCBS etc so i test from the board to my isolator with the isolator in the off position Or equipment disconnected at 500V. Then from the isolator to the AC unit at 250v. The i test the whole cct as a whole with LN joined together betwwen earth.

Hope this helps ya out

Cheers

JS