7.4 Prospective Fault Current and Short Circuit calculation (PFC & PSCC)
The prospective fault current and short circuit current of a circuit is automatically calculated when making a loop
impedance test. The calculation uses a nominal circuit voltage, not the actual circuit voltage, and is displayed above
the loop impedance measurement, as below:
The fault current is calculated using the expression:-
PSCC or PFC = Nominal supply voltage in Volts
Loop resistance in Ohms
Example :PSCC or PFC = 230 V / 0.13 Ω
= 1769 VA (displayed on the MFT as 1.77 kA)
The nominal supply voltage used in the calculation is automatically selected depending on the actual circuit voltage.
The instrument uses the following voltage values:-
Actual measured voltage Nominal voltage
< 75 V 55 V
≥= 75 V and <150 V 110 V
≥= 150 V and <300 V 230 V
≥=300 V 400 V
Z
max
test mode
Ideal for multiple loop measurements on a ring final circuit where the highest loop value is to be recorded.
Both
L-PE
and
L-N
L-L
test options can be used.
The current loop test value is displayed on the lower (larger) readout, whilst the maximum measured value of the
sequence is displayed on the upper (smaller) readout.
www.megger.com MFT1800 series
33
Loop impedance testing
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