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 MIL-HDBK-232A
5.2.3 Power panels. Power panels require no special installation other than
placement. Panels should, if possible, be located within the vicinity of the
equipment being served. If RED power is established, separate panels are
provided for RED and BLACK distribution. Nontechnical power will not be
mixed with technical power. Panels should be marked with appropriate use
labels.
5.2.4 Terminations. Equipment terminations should be consistent with
equipment design. If the equipment uses conventional ac plugs, plug boxes or
plugmolds should be located within the enclosure or rack. In all cases, the
runs from the power panels to the equipment shall be three continuous wires
run in a single run (for single phase use). In no case will the phase,
neutral, or ground conductors be run in separate conduits or ducts to
equipment.
5.2.5 Grounding. Grounding of power is in accordance with MIL-HDBK-419,
MIL-STD-188-124, and the National Electrical Code (NEC). Specifically, the
neutral conductor will be grounded to earth at the service transformer or
first service disconnect. The grounding point should be, in order of
precedence: (a) a network of earth driven rods forming the facility EESS, (b)
structural steel, (c) metallic cold water piping system, or (d) other
continuous metallic system. The installer and designer are cautioned to be
aware of grounding problems in some commercial equipment. MIL-STD-188-124
states, "The ac neutral shall be insulated from the equipment chassis and
case." Many items of commercial equipment and older Government equipment use
the chassis for a neutral reference. In such cases, it is not possible to
isolate the neutral and FPSS wire. The design engineer should group all such
equipment on a single power panel. This technique is meant to reduce the
safety hazard associated with tying these lines together. Grounding
techniques are also discussed in FIPS PUB 94, along with suggested solutions
for digital systems.
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