NAPIT Certification Scheme Proving Unit - Napit assessment

Clark3169 · Apr 5, 2013

SMB said:
Okay, this is being picky and my head is full of books at present (it won't be for much longer).

But this is the truth of it.

Someone, one day, will use the supply as their 'proving unit'. They will test the supply as 'live', they will isolate what they think is the supply, they will re-test on their 'dead' supply and during that time their voltage meter will have failed, be it batteries or mechanical failure. Then they will assume the supply is dead....and it isnt.

Stranger things have happened and its the law of averages that such an occurance will happen.

Im only playing devils advocate here. This is unlikely to happen, but this is why 'proving units' are the recommended way of showing your voltage meter is operating correctly, hence proving isolation of the circuit you are going to work on, and protecting your safety.

So, Mattmoo......your 'known supply' is free alright, unless the batteries run out just at the wrong time, then it could be pricey.

Unless your approved voltage indicator will work even without batteries. Just like this one

Martindale VT12 Voltage Indicator

i thought most did to be fair?

varilite · Apr 5, 2013

If its just a pure voltage tester no batteries but if it also does clever things like continuity it will require batteries

Clark3169 · Apr 5, 2013

That makes sense. Thanks.

GLENNSPARK · Apr 5, 2013

SMB said:
Hi.

Safe isolation as required to pass the 2391 examination is as follows...

* Gain permission to isolate (there maybe someone in a lift etc).

* Identify the circuit to be isolated.

* Isolate the circuit.

* Lock off the supply.

* Add warning labels at isolation source.

* Check your voltage tester with a proving unit.

* Test isolated supply terminals.

* Re-test voltage meter with proving unit.

Sounds like a pain in the bum, but on larger installations this process is safe and pretty much fail proof.

Its what it says on the tin....."safe isolation".

Regards.