UL 458:2006 pdf download – Power Converters/Inverters and Power Converter/Inverter Systems for Land Vehicles and Marine Crafts.
39 Dielectric Voltage-Withstand Test
39.1 A unit, at the maximum operating temperature reached in normal use, shall withstand for 1 mm without breakdown the application of a 60 Hz essentiaily sinusoidal potential of:
a) One thousand volts plus twice the maximum rated voltage:
1) Between the primary circuit and dead metal parts;
2) Between the primary and secondary circuits: and
3) Between all secondary windings. including any ferroresonant winding.
b) Five hundred volts between a secondary circuit operating at 50 V or less and dead metal parts; 1000 V plus twice the maximum rated secondary circuit voltage between a secondary circuit, including any ferroresonant winding, operating at more than 50 V and dead metal parts.
C) One thousand volts plus the rated voltage of a capacitor between the terminals of a capacitor used across the line for radio-interference elimination or arc suppess4on.
39,1.1 A dc potential of 1.414 times the rms value of the ac potential specified in 39.1 may be used instead of the ac potential.
39,2 To determine whether a unit complies with the requirenerits in 39.1, the unit is to be tested using a
500 VA or larger capacity transformer, the output voitage of which can be varied. The applied potential is
to be increased from zero to the required test value, and is to be held at that value for 1 mm. The increase
in applied potential Is to be at a substantially uniform rate as rapid as Is consistent with correct Indication
of its value by a voltmeter.
40 Induced Potential Test
4.0.1 If a 2.flange bobbin isolated power transformer is to be tested in accordance with (d) of the Exception to 17.2.3, the test specilied in 40.2 — 40.4 shall be conducted without breakdown of Insulation.
40.2 The primary winding of the 2-flange bobbin transformer is to be subjected to an alternating potential
of twice the rated voltage with the ends of all other windings opened. The potential Is to be applied for 7200 cycles or for 60 s. An essentially sinusoidal source is to be used, and the frequency of the source may be in the range of 120— 1000 Hz if necessary to reduce the likelihood of saturation of the transformer core.
40.3 Primary- and secondary-circuit wiring connected to the transformer is to be disconnected for this test.
40.4 The test voltage required in 40.2 is to be initiated at one-fourth or less of the full value and brought up gradually to the full value in not more than 15 s. After being held for the time specified. the voltage is to be reduced slowly, but within 5 s, to one-tourth of the maximum value or less, and the circuit opened.
41 Testing on Transformer Insulating Materials
41.1 It required by note (C) or (g) of Table 17.1. the transformer insulating material shall be subjected to the test described in 41.2.
41.2 The insulating material is to be placed between two opposing electrodes The electrodes are to be cylindrical brass or stainless steel rods 1/4 inch (6.4 mm) in diameter with edges rounded to a 1)32 in (0.8 mm) radius. The upper movable electrode is to weigh 50 ± 2 g to exert sufficient pressure on the specimen to provide good electrical contact. The test potential is to be increased to the test value and the rriaximum test potential is to be maintained for I s. The result is acceptable if there is no dielectric breakdown.
42 StraIn Relief Test
42.1 The strain relief means provided on a flexible cord shall withstand for 1 mm without csplacement a direct pull of 35 lbs (156 N) applied to the cord, with the connections within the unit disconnected. The strain relief is not acceptable if, at the point of disconnection of the conductors, there is such movement of the cord as to indicate that stress on the connections would have resulted.
42.2 A 35-lb (16-kilogram) weight is to be suspended from the cord and supported by the unit so that the strain-relief means will be stressed from any angle the constwction ol the unit permits.
42.3 A wiring lead intended for field connection (see and 62.4) shall withstand without damage or displacement a direct pull of:
a) 20 lbs (89 N) for 1 mm applied to a lead extending from the enclosure (such as through a knockout): and
b) 10 lbs (44.5 N) for 1 mm applied to a lead within a wiring compartment.