Fault Calculation Method

The fault calculations are based upon IEEE Std 242-2001: IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems.

The fault calculated is the three-phase line-to-line fault.

$$Fault = {Voltage \over \sqrt{Resistance^{2} + Reactance^{2}}}$$

The default feeder and branch circuit $Resistance$ and $Reactance$ values are based upon NEC Table 9. These values can be modified in the Wire Sizing command.

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

The fault calculation includes motor contributions for all devices with a "Motor" load type, such as Single Motor, Multiple Motors, or Heating and Cooling Motor. The motor current is equal to $Rated\>Current \times 4$. 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.