New to testing... Ze, PSCC & PEFC

[Geoffsd]

Hi all, new to testing myself, but after looking through a testing book, i've noticed that there are 2 tests that can be done for PSCC. The first one is as the original poster demonstrated in the pics (really helpful BTW) of testing at the incoming supply between L + N. The second being performed at the neutral bar and after the MCB/fuse for individual circuits.

One method of testing. It can be done wherever you require on a circuit.

I guess the point being that test 1 would be to test to check the main switchgear can handle the PSCC and likewise the MCB can also safely switch it's measured PSCC as well

Yes.

(the book shows 2 different amounts i.e main switch PSCC of 23kA and MCB of .82kA).

23kA ???

I get the impression that checking the PSCC for individual circuits is often overlooked or rarely performed. Anyone got any thoughts about this?

Probably because it is not recorded anywhere.
Zs, and so PEFC, is done at many points and if this is satisfactory then PSCC, because it is usually higher, will be as well.



The readings on the meter in the pictures do not match up or make sense.

 

[Bick]

One method of testing. It can be done wherever you require on a circuit.


Yes.


23kA ???


Probably because it is not recorded anywhere.
Zs, and so PEFC, is done at many points and if this is satisfactory then PSCC, because it is usually higher, will be as well.



The readings on the meter in the pictures do not match up or make sense.

Thanks for the reply Geoff. The values i've given are not calculated or anything, they are just given as 2 separate examples with what seem an emphasis on the individual circuits producing a smaller PSCC due to the fact that the smaller conductor size would be higher resistance. The point i was trying to make being that the main switch being able to handle a higher PSCC than the MCB therefore in a fault condition the mainswitch may be able to safely switch the fault but the MCB may not leaving it in a potentialy damaged state after a fault. Seeing as a Live/neutral fault on an individual circuit could potentially produce a higher fault current than a PEFC (CPC being a higher resitance IF smaller than main conductor). Add into the mix RCD's, that only protect earth faults and there is what seems to me a weak link in the chain (at least one that's being overlooked) maybe this is why the book is showing the 2 tests?? All highly speculative and worse case scenario and not sure my chain of thought is correct but i think you can sort of see my logic??

 

[Geoffsd]

Yes, but just to clarify, if I have understood, the main switch does not disconnect on a fault.

So Zs is to determine that the MCB will operate and Ze, the supply fuse.

I'm not sure what you mean by an RCD being a 'weak link' as they are rated for the same fault current as MCBs.

 

[TPES]

First time I've seen this but i am the only one who thinks there is something wrong with pic 2 where the guy thinks he is measuring PEFC?

Also I think the 3rd lead is only required where there is an RCD upstream.

Any thoughts?

What an old post!!!

So... What is your method of testing PEFC? How do you carry this test out? It maybe confusing for some people who only have 2 lead testers