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Three ways to get prospective fault currentMust you measure PFC?
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| Method | Note |
|---|---|
| Measurement | Do the loop test, then press the fault current button. This is how you get the maximum — record the greater of PSCC and PEFC, and check the device's breaking capacity is greater |
| Calculation | (Uo × Cmin) ÷ Zs gives the lowest fault current at that point — the figure for checking the device disconnects in time, not for breaking capacity |
| Enquiry | Ask the DNO for the figure |
The schedule says so. Next to Ipf it reads "by enquiry or by measurement" — so you are not obliged to measure it.
And the two faults it covers:
| Fault between | |
|---|---|
| PEFC — prospective earth fault current | Line to protective conductor (earth) |
| PSCC — prospective short-circuit current | Line to neutral, or line to line on three phase |
On the instrument. With three leads in you press one button and it cycles, deciding which value it is giving you. Some instruments want a two-lead test for one and a three-lead for the other — learn which yours does.
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