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This study determines the magnitude of current flowing throughout the power system at critical points during various time intervals after a “fault” occurs. These calculations are used to determine the bolted fault current which is essential for calculation of incident energy and interrupting ratings of your equipment such as circuit breakers and fuses. Accurate one line diagrams and equivalent utility capacity are required for this study.
Circuit breakers and fuses have overcurrent ratings and short circuit interrupting ratings. Overcurrent ratings identify the amount of electrical current the 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. In this short circuit study, we will calculate the fault current at various locations in the plant and compare to the interrupting ratings of the devices used at each location.
Equipment Evaluation Study
This study is an optional extension of a Short Circuit Study and compares equipment ratings with calculated short circuit and operating conditions. This will prevent extensive equipment and system damage and personnel injury because of underrated equipment in the event of a fault. The study will identify underrated equipment and recommend replacements. The NEC® requires that all short circuit interrupting devices have ratings sufficient for the current which must be interrupted.
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