Zero-Sequence Impedance and Incident Energy

A question that I am often asked either on-line or in one of my arc flash training classes is in regards to incident energy calculations and line-ground short circuit current:

“Since it is possible for the line-to-ground short circuit current to be greater than the three- phase current, could the line-to-ground condition be the worst case for incident energy calculations using IEEE 1584 equations?”

The short answer: No.

The longer answer: Let’s look at the equations for each short circuit calculation using symmetrical components.

The equation for calculating the three-phase fault current is: Continue reading