Determining Available Fault Current based on motor starting characteristics

This paper will discuss the techniques applied and results obtained by “reverse engineering” motor starting characteristics by both manual calculations on small electrical distribution systems and with electrical system analysis software on larger electrical distribution systems. The results of these calculations are then compared to actual values recorded in the field. While the Available Fault Current cannot be measured directly, the effect it has on the starting characteristics of large motors can be measured. These results can then be used to determine a range of Bounded Available Fault Current, which will produce motor starting characteristics within specific tolerances of those measured in the field.