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-3 -3 Short-circuit calculations for systems below 1500 kilowatts

The exact 46 CFR §111.51-3 text, rendered cleanly with its subsection structure — plus how this rule shows up on the exam.

Public-domain federal text · ingested from eCFR
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TL;DR

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:

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A DC shunt motor is running at rated speed when its field circuit opens accidentally. What is the most likely immediate result?

Section 111.51-3 — full text

Rendered cleanly from the source — the exact regulatory text, with subsection structure preserved.

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 8times the aggregate normal rated generator currents plus 3times the aggregate normal rated currents of all motors that may be in operation.

(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 8times the aggregate normal rated generator currents plus 3times the aggregate normal rated currents of all motors that may be in operation.

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A DC shunt motor is running at rated speed when its field circuit opens accidentally. What is the most likely immediate result?

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