Expected results of PFC test

[pumpkinbreath]

Hi all

I'm doing the last leg of 2330 Level 3 in a week and I know there is a section about expected test results. I'm up on everything but the Prospective fault current; I know that you write down the highest reading out of Prospective Earth Fault/Prospective Short Circuit Current on the schedule of test results but how do you judge what it's going to be without the experience of a veteran sparky??

At the start of the exam we are given an earthing arrangement to apply other results too, how does PFC differ with different arrangements??

Any thoughts are greatly appreciated...

 

[IQ Electrical]

It differs according to the external earth fault loop impedance in accordance with Ohm's Law:

I=V/R

Say Ze is 0.15 Ohms, your expected PFC will be approximately 230/0.15 = 1533A or 1.53 KA

If this is a 3-phase supply then the value can be multiplied by 1.732 to calculate the PFC or by 2 if you follow the advice of Guidance Note 3.

In a TN-C-S supply the PEFC and PSSC will be around the same value.

 

[pumpkinbreath]

Nice one IQ, thats very helpful. Cheers for your help