Fault Calculation Method

The fault calculations are based on IEEE Std 242-1975 Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems.

Fault = Voltage / sqrt(Resistance2 + Reactance2)

The feeder impedance values are based upon NEC Table 9. These values can be modified by the user.

The transformer impedance values are for dry-type indoor transformers. These values can be modified by the user.

The fault calculation includes motor contributions for all devices with a load type of Single Motor or Multiple Motors. The motor current equals 4 times the rated current of the motor. The X/R ratio of motors is 4. The impedance of the branch circuit wires from the motor to the panel is not included. These values cannot be modified by the user.


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