TM 5-852-9/AFR 88-19, Vol. IX
CHAPTER 5
ELECTRICAL
5-1. General. Electrical system design for buildings located in arctic and subarctic regions require some
special considerations. The following items require special treatment.
5-2. Grounding. It is very difficult to obtain an effective electrical ground in arctic and subarctic regions
because of soil and climatic conditions. The chance of finding and developing a low resistance grounding site
decreases greatly with movement towards polar regions from the zone of seasonal frost, to discontinuous and
then into continuous permafrost. Large seasonal variations in the resistance to ground can be expected in
areas of frozen ground. Grounding may not be difficult during summer months, but will likely become a
problem during the winter with seasonal freezing of the surface layer. Poor grounding results from an arid
climate, permafrost, and glacial till or other well drained soils. The normal practice is to ground at the service
entrance to the metallic water system piping. If satisfactory metallic water piping is not available, a driven
ground rod with a maximum allowable resistance of 25 ohms is required. If this 25-ohm requirement is not
met with one rod, up to three additional rods spaced a minimum of 10 feet apart should be driven to bring
the resistance down. Ground resistance can also be reduced by increasing the length of the ground rod. If
these measures fail to reduce the ground resistance sufficiently, the soil around the rod may be chemically
treated. Chemical treatment is a temporary measure and must be repeated periodically, with the time between
treatments depending on the rate of leaching by ground water. An effective ground cannot be achieved if the
ground electrode is completely enclosed in frozen soil. If a low resistance ground is vital in areas where the
soil is subject to freezing to great depths (8 feet or more), other methods of reducing ground resistance, such
as construction of ground wells or counterpoises are necessary. Natural thaw zones beneath lakes and
streams, the ocean, steel reinforcing bars, or metal well casings can provide good grounding alternatives. In
the final analysis, it may be impossible to achieve an adequate ground because of ice and snow cover. In that
case, electrical hazards may be minimized by obtaining surface area contact with the earth, or bonding all
electrical equipment. Using either method, extra safety precautions should be taken.
5-3. Lighting. The design of interior illumination for any heated building in arctic and subarctic regions is
the same as for other regions. In general, lighting intensities should be as recommended in the Illuminating
Engineering Society (IES) Lighting Handbook, subject to modifications and clarifications specified in AFM
88-15. The type of lighting must be coordinated with the architectural design to achieve the best
psychological effect, as noted in Chapter 2 of this manual. Where low ambient temperatures will normally
be encountered in interior and exterior areas, fluorescent or high intensity discharge type lighting fixtures with
low temperature ballasts should be used. On an economical basis, selection will be made by comparing initial
installation versus relamping maintenance costs. In design analyses, lighting loads will be used with 100
percent load factor.
5-4. Wiring methods. Except for the special requirements discussed below, wiring will be installed in
accordance with guide specifications. Conduit runs will be installed to provide sufficient water drainage.
Where fittings are installed on surface mounted raceways on exposed walls or floors, the roofs of heated
buildings, or in areas exterior to heated buildings, they will be of cast metal. Where outlet boxes are installed
flush with the exposed exterior surfaces of heated buildings, they may be of sheet metal with gasketed cast
metal covers. Exterior wiring will consist of insulated conductors installed in zinc-coated rigid steel conduits.
5-5. Vapor retarder penetrations. Frost buildup from moisture condensation on the heated side of roofs,
exterior walls, and floors must be prevented to the maximum practicable extent wherever electrical wiring
penetrates the vapor retarders of these surfaces. The following steps must be taken:
a. Conduits will be sealed, including interior voids between conductors and cables, and exterior voids
between raceways and building components.
b. Flush mounted boxes will be sealed for the full width and depth of voids between boxes and building
components.
c. Hack-to-back installation of boxes and equipment will not be permitted in roofs, exterior walls, or
floors.
d. On the warm side of boxes, vapor retarder and insulation will be compressed as required without
5-1
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