MIL-HDBK-1011/1
severe corrosive environments, the use of stainless steel (Type 316 or 326),
fiberglass enclosures, or aluminum alloy 5052 enclosures are recommended over
sheet metal raintight enclosures. Pressed steel outlet boxes set in any
concrete that is high in alkaline content are subject to corrosion. The use
of non-metallic outlet boxes and non-metallic conduit is recommended.
High Voltage Distribution (Above 600 Volts)
15.11
Underground Distribution. To achieve superior protection against
15.11.1
hurricanes and typhoons and salt-laden air, design power distribution for
underground installation, funds permitting. If direct buried cables are used,
protect the cables from physical damage with route markers, treat the soil
within 12 inches of the cable for termites, and install plastic polyethylene
warning tapes in the trench over the cables. Ensure that all ferrous
materials used in manholes or handholes are hot-dipped galvanized and coated
with epoxy or bituminous paint.
Overhead Distribution
15.11.2
15.11.2.1 Poles. Poles may be wood, metal, or prestressed concrete. (The
requirement for prestressed concrete poles is much more critical in hurricane
and typhoon areas than in areas where these extremely high winds occur.)
Protect all checks and cracks in wood poles and fill with a preservative
grease of 10 percent pentachlorophenol or other preservative. During or
immediately following pole installation, treat the soil 12 inches around and
down to the base of the pole with termiticide in areas infested by termites.
Ensure that wood poles are line-guyed and every fifth pole is guyed 4 ways,
and pole-top transformer banks are limited to sizes recommended in
MIL-HDBK-1004/2.
15.11.2.2 Pole Caps. To minimize leaching of wood preservative and to
prevent pole top decay, install pole caps on all pole tops prior to
installation.
Circular, low density polyethylene cover caps are commercially
available. The cover caps are secured by driving a 2 inch aluminum nail
through each of the tabs. Prior to securing the caps, apply a filler or
preservative paste material to eliminate any air space between the pole top
and the cover cap.
15.11.2.3 Conductors.
Use aluminum AAAC conductors in lieu of Type ACSR.
15.11.2.4 Insulators and Terminators. Insulators and terminators are subject
to flashover as a result of airborne salt build-up. Rate all insulators and
terminators for the next higher voltage level above the system voltage. After
installation, coat insulators and terminators with silicon grease for
additional protection against flashover. Heat shrinkable skirt type creepage
extenders, in accordance with MIL-HDBK-1004/2, may be used to provide
additional flashover protection in high salt-air environments.
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