ANSI UL 458 - Live Parts

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UL COPYRIGHTED MATERIAL –

NOT AUTHORIZED FOR FURTHER REPRODUCTION OR

DISTRIBUTION WITHOUT PERMISSION FROM UL

13.6 The power supply of a circuit as mentioned in 13.5 that is not limited to available energy in

accordance with 13.5(b), but the circuit includes either one or more resistors, a fuse, a non-adjustable

manual-reset circuit protective device, or a regulating network – see 13.9 – need not be investigated if the

current is limited in accordance with 13.7, 13.8 or 13.9.

13.7 A fuse or non-adjustable manual reset circuit protective device provided in the secondary circuit that

is used to limit the current in accordance with 13.6 shall be rated or set at not more than the values

speciﬁed in Table 13.1.

13.8 A fuse or circuit protective device may be connected in the primary of the transformer to limit the

current in accordance with 13.6 provided that the protection is equivalent to that speciﬁed in 13.7 as

determined by the Overcurrent Protection Calibration Test, Section 44.

Table 13.1

Rating for secondary fuse or circuit protector

Circuit voltage (V rms) Maximum overcurrent protection (A)

20 or less 5

More than 20 but less than 60 100/V

V is the maximum output voltage, regardless of load, with the primary energized in accordance with 31.1.

13.9 One or more resistors or a regulating network used to limit the current in accordance with 13.6 shall

be such that the current under any condition of loading including short circuit does not exceed 8 amperes

measured at 1 minute of operation.

13.10 If a regulating network is used to limit the voltage or current in accordance with 13.5 – 13.9, each

component of the regulating network should be short circuited or open circuited separately to determine

that the voltage or current does not exceed the maximum allowable values with the components faulted.

13.11 In a circuit of the type described in 13.6, the secondary winding of the transformer, one or more

resistors, a fuse or a non-adjustable manual reset circuit-protective device, or a regulating network, and

all wiring up to the point at which the current, voltage or both are limited shall be judged as primary

circuits.

14 Live Parts

14.1 A current-carrying part shall be of silver, copper, a copper alloy, or other material acceptable for the

application.

14.2 Plated iron or steel may be used for a current-carrying part if acceptable in accordance with 3.1, or

in a secondary circuit rated 30 volts rms (42.4 volts peak) or less; but unplated iron or steel is not

acceptable. Stainless steel and other corrosion-resistant alloys may be used for current-carrying parts.

14.3 An uninsulated live part shall be secured to an insulating base or mounting surface so that it will be

prevented from turning or shifting in position if such motion might result in a reduction of spacings below

the minimum acceptable values.

DECEMBER 14, 1993 UL 458 27