MIL-HDBK-1011/1
15.11.2.5 Hardware. Ensure that ferrous metal hardware are hot-dip
galvanized, and that aluminum guys with concrete anchors are in accordance
with MIL-HDBK-1004/2.
15.11.3
Transformers and Switchnear
15.11.3.1 Distribution Transformers. Generally, use pad-mount type
transformers, undercoated where installed outdoors. Use liquid-filled sealed
type transformers, without the breather pipe, or dry type, totally enclosed
self-cooled, for less than 600-volt application. Where transformers are
located in a vault, cast core dry transformers are recommended for their
inherent fungus resistance and lack of fire-rated enclosure requirement.
15.11.3.2 Switchgear. Enclose switchgear in metal. Include all switchgear
enclosures with thermostatically controlled space heaters for humidity
control.
Due to fewer exposed contacts, primary vacuum breakers are
recommended over air breakers or fusible interrupters. Seal control relays
where provided in dusty or humid environments.
15.11.3.3 Protective Shelters. In the tropics all ferrous items are highly
susceptible to accelerated corrosion when exposed to the weather. Also,
damage to the protective coating on equipment can be expected during routine
operational inspection and maintenance of transformer and switchgear
facilities. Furthermore, hurricane and typhoon damage reports indicate that
these exterior type installations are very susceptible to damage by flying
debris. Protect pad-mounted transformer and switchgear installations in
hurricane- and typhoon-prone areas from the weather with a structural shed-
type enclosure of either concrete and masonry.
15.11.3.4 Fiberglass Reinforced Enclosures. In areas with severe corrosion
potential, provide reinforced molded one-piece fiberglass enclosures for pad-
mounted switchgear and transformers if they are installed outdoors.
Service and Distribution (600 Volt and Below)
15.12
15.12.1
Switchboards and Motor Control Centers. Switchboards and motor
control centers may be of the standard manufacturers design. It is
recommended that all switchboards and motor control centers be installed in
enclosed buildings. If installed outdoors, provide a fiberglass housing.
Standard factory-finished ferrous weatherproof housings do not provide
satisfactory service life.
15.12.2
Panelboards.
For panelboards use the circuit breaker type, copper
bussed, located in the interior of buildings or within enclosed spaces. Use
bolt-on rather than plug-on breakers to minimize contact corrosion problems.
If a panelboard is located on the exterior of a building, provide a fiberglass
enclosure around the panelboard. Standard rain caps on factory modified
panelboards do not afford sufficient protection against driven rain.
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