Fault current.

Wayne Phillips · Mar 20, 2013

Dear Forum,

Can anyone explain in simple language what the difference is between P.F.C. and P.S.C.C. and how is each calculated?

Thanks,

Wayne:dizzy2:

KFH · Mar 20, 2013

Prospective Fault Current = current to an earth fault.
Prospective Short Circuit Current = L-N fault current.
Calc I=V/R V= 230 R= Your Ze/Zs for PFC depending on where in the circuit you want to know PFC. For PSCC you use the same calc using the loop resistance of L-N. Or you press the button on the tester to give you the answer.

Edit Getting my PFC confused with PEFC see Richards much better description below:dunce2:

ian.settle1 · Mar 20, 2013

You tell us what you think it is and we will tell you if you are right or wrong

Richard Burns · Mar 20, 2013

PFC is the prospective fault current. I.e. this is the highest current that can be expected to flow in the case of any fault in the circuit. It is the highest value obtained from the PSCC or the PEFC.

PSCC is the prospective short circuit current. I.e. this is the highest current that can be expected to flow in the case of a short between a line conductor and the neutral conductor or between two line conductors.

There is also PEFC, prospective earth fault current, this is the highest current that can be expected to flow in the case of a fault from a live conductor to earth.

These are not normally calculated but measured using a test meter.

You can calculate PEFC using the earth fault loop impedance measured with all bonding in place and the nominal voltage of the supply using ohms law.

PSCC in three phase systems is often calculated by measuring the phase to neutral fault current and multiplying by the rule of thumb value of 2, to give the likely (actually higher than it would be in reality) phase to phase short circuit current. This is where the meter cannot measure between phases directly.

GLENNSPARK · Mar 20, 2013

voltage available divided by the impedance will generate the fault current that can flow (at that part of the installation)
the PFC for 3 phase will be the Zpp...or Zpn x2...or Zpn x square route of three
PSCC will always be higher than PEFC for 3 phase...
it is used to verify whether...or not the protective devices will be able to handle the fault current (at the part of the installation where such protective devices are being utilised)....and so it follows: the further away from the origin of supply...the higher the impedence and as such the lower the PFC will be....so for example:
As Ze will be of a lower impedence than say Zdb...so the levels of fault current will be higher at the origin of supply than further downstream....
on single phase we take the highest of the 2 (PEFC & PSCC)...and its the highest of these that will be the PFC...