Earth Fault Current Calculation
ΤΤ Earthing System:
With:

the phase to neutral voltage


the impedance of the supply


the impedance of the earthing electrode


the impedance of the phase conductor


the impedance of the CPC


The voltage factor Cmin is to take into account the worst case voltage variations conditions in a low voltage installation, specified in IEC 60909 as 0.95

ΤN Earthing Systems:
With:

the phase to neutral voltage


the exterior impedance


the impedance of the phase conductor


the impedance of the protective CPC


The voltage factor Cmin is to take into account the worst case voltage variations conditions in a low voltage installation, specified in IEC 60909 as 0.95


Adiabatic Check of the Protective Conductor During Earth Fault
The software, in accordance with regulation (543.1.3), makes use of the earth fault current, together with the operating time that has been found from the timecurrent curve of the protective device, in order to obtain a lower bound on the crosssectional area of the protective conductor (CPC):
With:

the minimum crosssectional area of the protective conductor in mm2


the cable factor

If the operating time is less than 0.1 sec, then

Is the letthrough energy characteristic of the protective device

Otherwise,

is the earth fault current


is the operating time taken from the timecurrent curve of the protective device

Note: If the protective device is an RCD or RCCB, then the software makes the check using for t the operating time of the RCD or RCCB.
Note: Impedances under fault conditions are calculated in accordance with Guidance Note 1: Table E2.
