Short circuit currents represent a tremendous amount of destructive energy, which can be released through electrical systems under fault conditions. Every electrical system confines electrical current flow to selected paths by surrounding the conductors with insulators of various types. Short circuit current is the flow of electrical energy that results when the insulation barrier fails and allows current to flow in a shorter path than the intended circuit.

Overcurrent ratings identify the amount of electrical current a device may withstand without a fuse blowing or circuit breaker tripping. The interrupting rating is the maximum electrical current the device can interrupt before it fails. In the event of a fault, a device may trip or fail depending on the manufacturer’s short circuit interrupting rating. A short circuit study requires calculation of the fault current at various locations in the plant and comparison to the interrupting ratings of the devices used at each location.

A short circuit study should be performed when an electrical system is first designed, and then updated when major modifications or renovation takes place — but no less frequently than every five years. Major changes would be considered a change in feed by the electric utility, in the primary or secondary system configuration within the facility, in transformer size or impedance, in conductor lengths or sizes, in type of circuit breaker, or a change in the motors that are energized by the system.

With today's high fault currents, it's more important than ever to protect electrical equipment from extremely high current levels. Otherwise, the equipment may explode as it attempts to interrupt the fault.