Short Circuit & Coordination Studies

A Short Circuit and Coordination Study is one of the most important steps you may ever take to protect your personnel and electrical distribution system. When an electrical fault or overload exceeds the interrupting rating of the protective device, the consequences can be devastating including injury, damaged electrical equipment, and costly downtime.

Coordinated Power Engineering (CPE) will perform a Short Circuit Study using a computer model that determines the 'worst case' fault level at the electrical distribution equipment. The fault levels are compared to the existing device interrupting ratings to determine if the protective devices are rated in accordance with the manufacturer's published data and applicable standards. If required, new ratings will be determined.

A Coordination Study looks at the protective devices from a slightly different angle to determine how to set protective devices in order to minimize the area of an outage. Selectivity of the protective devices is determined so that a fault can be interrupted within the affected circuit, thereby, minimizing the power disruption. Protection requirements are also analyzed.

The IEEE Electrical Power Distribution for Industrial Plants (Red Book) describes the purpose of Electrical Coordination Studies as follows:

    The primary purpose of a coordination study is to determine satisfactory ratings and settings for the electric system protection devices. The protection devices should be chosen so that pickup currents and operating times are short but sufficient to override system transient overloads such as inrush current experienced when energizing transformers or starting motors. Further, the devices should be coordinated so that the circuit interrupter closest to the fault opens before other devices.

    Determining the ratings and settings for protective devices requires familiarity with NEC requirements for the protection of cables, motors, and transformers, and with ANSI/IEEE C57.12.00-1980 for transformer magnetizing inrush current and transformer thermal and magnetic stress damage limits.

For more on Short Circuit & Coordination Studies, call CPE at (410) 694-9494 or e-mail