TM 5-852-9/AFR 88-19, Vol. IX
e. Nonhardening material will be used for sealing raceways and boxes so that it can be moved without
damaging electrical wiring, raceways, boxes, etc.
f. Vapor retarder will be sealed to boxes and equipment wherever practicable.
g. Boxes and raceways will be installed on the warm side of vapor retarder where practicable.
5-6. Electrical insulation. The insulation on electric wires will be of cross-linked polyethylene, or silicone
rubber, or other moisture-resistant type that has been proven satisfactory for arctic low-temperature use.
5-7. Switches. Some switches are affected by the ambient temperature. Mercury switches should not be
specified for use where the temperature drops to 400 F, as mercury solidifies at this temperature, and
switches will not function.
5-8. Miscellaneous items.
a. Thermally operated protective devices. A thermally operated protective device is located such that
the ambient temperature is approximately the same for the device and the conductor; therefore, low
temperatures are no problem. If the protective device is located outside of a heated building and the
conductors are inside, however, the temperature differential must be considered. Ambient compensated
circuit breakers which are effective to a temperature of about &20EF are available. In unheated areas,
enclosures for switches and circuit breakers should be gasketed and weatherproofed to keep the devices
moisture free.
b. Service entrance. Underground service will be provided wherever practicable. Where required, an
overhead service entrance should be located so that it will not be subject to damage from ice forming on
eaves. A service entrance should be installed in the gable end of the building or on the roof by bringing a
conduit up through the roof overhang and mounting a weatherhead on top. The gable location is preferred
because of flashing and support problems introduced by the roof penetration.
c. Transformer vaults. In some subarctic areas, corrosive conditions resulting from wind driven rain,
snow, and salt spray are so severe that it is desirable to provide vault space inside buildings for transformers
and associated service equipment.
5-2
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