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.

Page url: http://www.designmaster.biz/docs/elec/index.html?fault_calculation_method.htm
©2012 Design Master Software, Inc