PFC Testing

[Mark213]

When testing PFC is it ever acceptable to test with Main Switch On, all MCBs On and from the Outgoing Side at DB.

The methods I have seen instructed were with the supply isolated from the supply and on the Incoming Supply terminals,
but was shown the way described in the first sentence by someone.

Thanks.

 

[timhoward]

Interesting question.
Normally, circumstances would be that you'll have just previously done the Ze, and as you've disconnected the main earthing conduction the main switch would be off and locked out.
While it wouldn't make a material difference where the Live probe is connected, and the test results would be more or less unaffected, I think this would technically contravene regulation 14 of the electricity at work regulations, as it has to be unreasonable for it to be dead (it isn't) and it has to be reasonable in all circumstances for it to be live.
Having live bus-bars and additional live parts for no valid reason is not reasonable really.
Is it acceptable - probably not but I'm sure it happens every day!

 

[timhoward]

Having written all that, I've just remembered that my NAPIT assessor asked me to do exactly that, a PSCC test while the entire board was live....
So it must be fine ??

 

[Dartlec]

Interesting question.
Normally, circumstances would be that you'll have just previously done the Ze, and as you've disconnected the main earthing conduction the main switch would be off and locked out.
While it wouldn't make a material difference where the Live probe is connected, and the test results would be more or less unaffected, I think this would technically contravene regulation 14 of the electricity at work regulations, as it has to be unreasonable for it to be dead (it isn't) and it has to be reasonable in all circumstances for it to be live.
Having live bus-bars and additional live parts for no valid reason is not reasonable really.
Is it acceptable - probably not but I'm sure it happens every day!

PFC is done with all earthing reconnected (as well as L-N to get the highest possible result of either option).

So in theory there is no practical reason I can see why the test result would be different if main switch is on or not or indeed all circuits live. (Could reverse harmonics of some sort affect the result, I don't know...)

That's different from how work can/must be carried out safely - but I think if all electricians "worked to rule" and turned the main switch off before removing any CU lid, a lot less work would get done...

 

[brianmoooore]

It's a bit like the driving test. There's the way you drive while being tested, and the way you drive once you've passed the test.

 

[pc1966]

That's different from how work can/must be carried out safely - but I think if all electricians "worked to rule" and turned the main switch off before removing any CU lid, a lot less work would get done...

Personally I would never remove the cover of an "unknown" CU with power on just in case!

But if you know the internals are safe than yes, it is fair enough to remove cover and do some testing with power on.

 

[Mark213]

Having written all that, I've just remembered that my NAPIT assessor asked me to do exactly that, a PSCC test while the entire board was live....
So it must be fine ??

Thanks for the rely.
Yes thats where I done mine under exam condition haha.
I practise with Main Switch Off but the examiner told me to do it with switch and breakers On.?

 

[Mark213]

Personally I would never remove the cover of an "unknown" CU with power on just in case!

But if you know the internals are safe than yes, it is fair enough to remove cover and do some testing with power on.

I think you also explained to me on a previous thread that it does not matter if you test PFC after the Main Switch along the circuit as the reading would be lower because of the extra resistance from the circuits cables.
i.e Amps go down as Resistance goes up.