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Table 17.2
Spacings within a transformer
Potential involved, volts Minimum spacing through air and over surface, inch (mm) between any
uninsulated live part and an uninsulated live part of opposite polarity, or the
core
a
0 – 50 3/64 (1.2)
50 – 125 1/16 (1.6)
125 – 250 3/32 (2.4)
250 – 600 1/4 (6.4)
a
Includes turns of a coil having a magnet wire coating.
18 Resistors
18.1 A resistor shall be reliably supported and the assembly shall be prevented from loosening or rotating
by a means other than friction between surfaces.
18.2 The use of a lock washer is considered to comply with the requirement in 18.1.
19 Switches and Controllers
19.1 A switch or other control device shall have current and voltage ratings not less than those of the
circuit that it controls when the converter or inverter is operated as intended.
19.1 effective April 13, 1993
19.2 A primary-circuit switch that controls an inductive load having a power factor less than 75 percent,
such as a transformer or some ballasts, and does not have an acceptable inductive rating, shall be rated
not less than twice the full-load current rating of the load, or the switch shall be investigated for the
particular application.
19.3 A switch that controls a tungsten-filament lamp shall have a tungsten-filament-lamp current rating
not less than the maximum current it will control.
Exception: A switch not having an acceptable tungsten-filament-lamp current rating and rated 3 amperes
or more may be used to control a 15-watt or smaller lamp.
20 Overload-Protective Devices
20.1 General
20.1.1 A protective device, such as a fuse or manually operable protector, the normal functioning of which
requires renewal, resetting, or replacement, shall be in a readily accessible location when the converter is
installed in accordance with manufacturer’s installation instructions.
20.1.2 If more than two circuit breakers are employed, a means shall be provided for disconnecting all
conductors in a recreational vehicle from the power-supply assembly.
DECEMBER 14, 1993UL 45834
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