UL 363:2015 pdf download – Knife Switches.
17.3 For the test mentioned in 17.2:
a) The open-circuit voltage of the power-supply circuit is not to be less than the maximum rated voltage of the switch;
b) The avadable rms symmetrical short-circuit current in amperes is not to be less than 5000. 7500 or 10.000 A. as appropriate;
C) The circuit is to be as indicated in Figure 25.1 External overcurrent protective devices are to be connected where the CL fuses are indicated. See 17.4; and
d) The power factor of the circuit is to be 0.45 — 0.50. lagging.
17.4 The overcurreni protective devices inccated in 17.2 are to be externally connected Class H fuses of the maximum rating for the case size of the rating specified or circt breakers of the type and rating indicated by the marking.
17.5 The tests specified in 17.2 may be performed without overcurrent protective devices if it can be shown that the test-circuit current was maintained for a period of time at least equal to the opening time of the specified overcurrent protective devices at the level of current involved.
17.6 For the performance of the test. the line and load terminals of the switch are to be connected to the corresponding test-circuit terminals by short copper-wire leads, maximum of 4 ft (1.22 m) per terminal, each of which has an ampacity not less than the current rating of the switch.
Exception: Cable length as provided for n 17.7 need not comply with this requirement.
17.7 If the physical arrangement of the test facilities requires leads longer than specified in 17.6, the
additional length of leads shall be included in the circuit calibi’ation.
18 Low-Level Dielectric Voltage-Withstand Test
18.1 Unless the same representative switch Is to be subjected to the Closing Test, a switch that has been subjected to the Short-Circuit Withstand Test shall be capable of withstanding for 1 minute without breakdown the application of a 48 — 62 Hz essentially sinusoidal potential:
a) Between line and load terminals with the switch open:
b) Between terminals of opposite polarity with the switch closed; and
c) Between live parts and dead metal.
18.2 The test potential shall be twice the voltage rating of the switch but not less than 900 V.
18.3 To determine if a switch complies with the requirements in 18.1. the test is to be made using a 500 VA or larger transformer, the output voltage of which can be vaned. Starting at zero, the applied potential is to be increased until the required test value is reached and held at that value for 1 minute. The increase in the applied potential is to be at a uniform rate and as rapid as consistent with its value being correctly indicated by a voltmeter.
Exception: The transformer may be less than 500 VA, it the output voltage is measured directly.
19 Closing Test
19.1 A representative switch shall be closed on a current magnitude equal to the short-circuit withstand rating. After the fault has deared, the switch shall comply with the requirements specified in 172 (a), (b), and (C).
192 The switch for this test is to be that used for the Short-Circuit Withstand Test, or a previously untested switch may be employed. The conditions of the Closing Test are to be the same as for the Short-Circuit Withstand Test, 17.3 — 17,7, Complete physical closure of the switch contacts need not be established.
Exception No. 1: Switches rated more than 1200 A at 240 V or less, and switches rated more than 600 A at more than 250 V. need not comply with this requirement.
Exception No. 2: Any other switches marked: For isolating use only -. need not comply with this requirement
20 Low-Level Dielectric Voltage-Withstand Test (Repeated)
20.1 The Dielectric Voltage-Withstand Test described in 18.1 18.3 shall be conducted following the Closing Test,
Exception No. 1: Switches rated more than 1200 A at 240 V or less, and switches rated more than 600 A at more than 250 V. need not comply with this requirement.
Exception No. 2: Any other switches marked.’ For isolating use only , need not comply with this requirement.