C.F.R. » Title 46 » CHAPTER I—COAST GUARD, DEPARTMENT OF HOMELAND SECURITY › SUBCHAPTER J—ELECTRICAL ENGINEERING › PART 111—ELECTRIC SYSTEMS—GENERAL REQUIREMENTS › Subpart 111.51—Calculation of Short-Circuit Currents and Coordination of Overcurrent Protective Devices

46 C.F.R. § 111.51-3

Short-circuit calculations for systems below 1500 kilowatts

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The following short-circuit assumptions must be made for a system with an aggregate generating capacity below 1500 kilowatts, unless detailed computations in accordance with § 111.51-4 are submitted:

(a) The maximum short-circuit current of a direct current system must be assumed to be 10 times the aggregate normal rated generator currents plus 6 times the aggregate normal rated currents of all motors that may be in operation.

(b) The maximum asymmetrical short-circuit current for an alternating current system must be assumed to be 10 times the aggregate normal rated generator currents plus 4 times the aggregate normal rated currents of all motors that may be in operation.

(c) The average asymmetrical short circuit current for an alternating-current system must be assumed to be 8 1/2 times the aggregate normal rated generator currents plus 3 1/2 times the aggregate normal rated currents of all motors that may be in operation.