Fault Calculation Basis

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

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

The default feeder $Resistance$ and $Reactance$ values are based upon NEC Table 9 and can be modified using the Wire Ampacities command.

The default transformer impedance values are for dry-type indoor transformers. These values can be modified using the Panel Edit command or Family Edit command.

The fault calculation includes motor contributions for all devices that have the Load Sub-Classification Motor Revit parameter enabled. This parameter is set on the connector element of the device family, in the Electrical - Loads section of the Properties panel.

The circuit length from the motor to the panel is accounted for. By default, the motor current is equal to $Rated\>Current \times 4$ and the X/R ratio of motors is 4. These values can be modified using the Instance Edit command or Family Edit command.

The fault is not calculated for circuits that have more than three branch circuit devices connected.