W-C-375E
4.7.9 Dielectric withstanding voltage.
4.7.9.1 Method I (see 3.12). Circuit breakers shall be tested in accordance with method 301, MIL-STD-202. The following details shall apply:
a. Magnitude of test voltage: 1,000 volts (rms) plus twice the voltage which may be applied between the parts specified below when the circuit breaker is connected to a circuit of its maximum voltage rating.
b. Nature of potential: AC 60 Hz.
c. Points of application of test voltage:
(1) Between line and load terminals with the breaker open: With the breaker in the "tripped" or the "off" positions.
(2) Between terminals of opposite polarity with the breaker closed.
(3) Between live parts and the overall enclosure with the breaker both open and closed. d. Measurement during test: Leakage current.
e. Examination after test: Circuit breakers shall be examined for evidence of flashover, mechanical damage, arcing, and breakdown.
4.7.9.2 Method II (see 3.12). Circuit breakers shall be tested as specified in 4.7.9.1, except the magnitude of the test voltage shall be two times the rated voltage of the circuit breaker but not less than 900 volts.
4.7.10 200 percent calibration at 25°C ±3°C (see 3.13). Circuit breakers shall be subjected to the 200 percent calibration test at 25°C ±3°C as specified in 4.7.2.
4.7.11 Short-circuit interruption (see 3.14). The power source, loading, instrumentation, calibration, wiring, and preparation for test shall be in accordance with the applicable portions of UL 489. Circuit breakers shall be tested in the enclosure specified (see 3.1). Openings may be provided in the enclosure if the combined area of all openings does not exceed 10 percent of the total external enclosure area and if no opening is directly opposite a vent in the circuit breaker case. The test enclosure shall be connected through a fuse as indicated in 4.7.3 to the line lead least likely to arc to the enclosure, or the neutral, if the circuit breakers are rated 120/240 or 277/480 volts ac. The connection is to be made to the load side of the limiting impedance by means of No. 10 AWG copper wire no more than 6 feet in length. The capacity of the supply circuit together with the total limiting impedance of the circuit shall be such as to permit the applicable current indicated in table XV. The open circuit voltage shall be not less than 100 percent nor more than 105 percent of the rated voltage of the circuit breaker under test, and the power factor of the test circuit with the required current flowing shall be in accordance with table XII. The operation shall consist of closing the short-circuit on the circuit breaker by means of suitable switching device, using random closing. After a 2- minute interval, or the time necessary to allow the circuit breaker to reset, but not more than 1 hour, the circuit
breaker is to be closed on the short circuit. Circuit breakers tested under "bus bar conditions" require only one operation, that being closing of the test circuit on the circuit breaker. Following the test, circuit breakers shall be
checked for damage to the circuit breaker case, ejection of wire from the wire connector or burn off of leads, failure of
a pole to trip, burned out shunts, bi-metals or heaters, mechanical failures which do not permit relatching or reclosing of the circuit breaker and other similar failures.
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