ANSI UL 458 - Induced Potential Test; Testing on Transformer Insulating Materials; Strain Relief Test

To Next Page

To Previous Page

UL COPYRIGHTED MATERIAL –

NOT AUTHORIZED FOR FURTHER REPRODUCTION OR

DISTRIBUTION WITHOUT PERMISSION FROM UL

40 Induced Potential Test

Section 40 effective April 13, 1993

40.1 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 speciﬁed 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 seconds. 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 seconds. After being held for the time speciﬁed, the

voltage is to be reduced slowly, but within 5 seconds, to one-fourth of the maximum value or less, and the

circuit opened.

41 Testing on Transformer Insulating Materials

Section 41 effective April 13, 1993

41.1 If 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 inch

(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

maximum test potential is to be maintained for 1 second. 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 minute without displacement

a direct pull of 35 pounds (156 N) applied to the cord, with the connections within the converter or inverter

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.

42.1 effective April 13, 1993

42.2 A 35-pound (16-kilogram) weight is to be suspended from the cord and supported by the converter

or inverter so that the strain-relief means will be stressed from any angle the construction of the converter

or inverter permits.

42.2 effective April 13, 1993

OCTOBER 15, 2004UL 45858