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e-CFR data is current as of November 25, 2020

Title 46Chapter ISubchapter JPart 111 → Subpart 111.52


Title 46: Shipping
PART 111—ELECTRIC SYSTEMS—GENERAL REQUIREMENTS


Subpart 111.52—Calculation of Short-Circuit Currents


Contents
§111.52-1   General.
§111.52-3   Systems below 1500 kilowatts.
§111.52-5   Systems 1500 kilowatts or above.

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§111.52-1   General.

The available short-circuit current must be computed—

(a) From the aggregate contribution of all generators that can simultaneously operate in parallel;

(b) From the largest probable motor load; and

(c) With a three phase fault on the load terminals of the protective device.

[CGD 74-125A, 47 FR 15236, Apr. 8, 1982, as amended by CGD 94-108, 61 FR 28279, June 4, 1996]

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§111.52-3   Systems below 1500 kilowatts.

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 §111.52-5 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 six 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 four 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 812 times the aggregate normal rated generator currents plus 312 times the aggregate normal rated currents of all motors that may be in operation.

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§111.52-5   Systems 1500 kilowatts or above.

Short-circuit calculations must be submitted for systems with an aggregate generating capacity of 1500 kilowatts or more by utilizing one of the following methods:

(a) Exact calculations using actual impedance and reactance values of system components.

(b) Estimated calculations using NAVSEA DDS 300-2 (incorporated by reference, see 46 CFR 110.10-1).

(c) Estimated calculations using IEC 61363-1 (incorporated by reference; see 46 CFR 110.10-1).

(d) The estimated calculations using a commercially established analysis procedure for utility or industrial applications.

[CGD 94-108, 61 FR 28279, June 4, 1996, as amended by USCG-2003-16630, 73 FR 65197, Oct. 31, 2008]

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