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 MIL-HDBK-232A
5.2.1.3.1 Dedicated service. A large facility would most likely be served
by a dedicated feeder transformer. This may be a delta-wye configuration
providing three phase leads and a neutral conductor grounded at the
transformer or first service disconnect. A fifth wire is included as the
fault protection subsystem (FPSS) (see figure 21) to provide a return path
for fault currents. Some isolation may be available through the transformer.
Filtering may be required if testing indicates insufficient suppression of
PLC. Care must be taken during installation and design to assure the loads
are balanced across the phases to reduce neutral currents.
5.2.1.3.2 Pole power. A smaller facility may be served by a single phase
pole transformer. In such cases, two energized leads, a neutral conductor,
and an FPSS conductor are provided (see figure 22). As in the large
facility, testing must be conducted to determine the extent of PLC and the
preventive measures required. This application is served well by an MG which
isolates the load from the source. Such MGs should use a dielectric shaft
between the motor and generator with separated housings.
5.2.1.3.3 Shared power. A smaller facility may be served from the source
for the entire building in which it is located. In such cases, significant
problems arise in controlling PLC and accounting for the distribution of
power. Filtering is indicated if RED power is required. An MG is also
appropriate if RED power is needed.
5.2.2 Power systems. Two power systems are usually established within each
facility -- non-technical power and technical power (see figure 2).
5.2.2.1 Nontechnical power. Nontechnical power is established to provide
heating, lighting, ventilation, and other services that are not required for
full continuity of operation. Nontechnical service is provided to prevent
equipment upset in the event of drops and surges caused by other equipment
cycling. Motor-driven fans, blowers, and pumps are inherent surge sources.
No special treatment is normally required, except that distribution should be
in conduit or armored cable with the conduit or armor grounded. Nontechnical
power is provided separately from technical power. Additionally, the
distribution should be designed so that nontechnical power cannot be used to
power the technical equipment. The need to filter utility power should be
determined on a case-by-case basis. The designer or installer may have no
control over the way nontechnical power may have been installed in the
facility. In such cases, the design and installation of the remainder of the
facility require that more stringent controls be established.
5.2.2.2 Technical power. Technical power is provided to power that
equipment which supports the mission. It is distributed in areas as required
and may be further divided into RED and BLACK power. RED power is created by
filtering selected lines a nd controlling distribution (see figure 23) or by
using MGs. Application of filtering is specified in paragraph 5.2.6.
5.2.2.3 Distribution. Distribution of power should be in metallic duct,
wire way, or conduit. Flexible conduit may be used for short runs from wire
ways or junction boxes to equipment ("short" means no longer than necessary
for vibration or minor placement adjustment). Care must be exercised to
ensure the electrical integrity and conductivity between the wire
way/junction box and equipment case, because flexible conduit often uses
plastic or nonconducting bushings in fittings that jeopardize continuity.
Where RED and BLACK power are established, each shall be distributed
separately. Power is not run in ducts with any other cable. Nontechnical
and technical power should be distributed in separate ducts/conduits (see
4.2.2.1 and 4.2.2.2).
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