MIL-HDBK-1191
C.2.3.1
Power Quality. The facility power system must provide the
specified nominal voltage (480 V or 240 V) plus or minus 5 percent to
each universal room. Special power conditioning equipment, if required,
should be identified and provided with the X-ray installation.
C.2.3.2
Three-Phase Rooms. If the room will receive three-phase
X-ray equipment, provide 150 amp, 480 volt, three-phase (3-wire and
ground) service to the room. Provide an adjustable trip, 150 amp,
3-pole, shunt trip circuit breaker in a NEMA 1, flush mounted enclosure.
C.2.3.3
Single-Phase Rooms. If the room will receive single-phase
X-ray equipment, provide 150 amp, 240 volt, single-phase (3-wire and
ground) service to the room. Provide an adjustable trip, 100 amp,
2-pole, shunt trip circuit breaker in a NEMA 1, flush mounted enclosure.
C.2.3.4
Emergency Shutdown. Provide a large, clearly identified
push-button to actuate the shunt trip circuit breakers, and disconnect
all power to the X-ray machine and accessories.
C.2.3.5
120/208 Volt Auxiliary Panelboard. If required by using
Military Department, provide a 120/208 volt, single-phase, 100 amp
panelboard with a 50 amp shunt trip main breaker to support the
single-phase loads in each room. Provide a 20-pole-space panelboard with
at least two 20 amp 2-pole circuit breakers, and five 20 amp 1-pole
circuit breakers. This panelboard may be served from the nearest general
purpose 120/208V transformer; a dedicated stepdown transformer may be
provided and fed from the 480V service in 3-phase rooms. (Calculations
should be based on 180 amp maximum demand for 3-phase rooms, and 300 amp
maximum demand for single-phase rooms.)
C.2.3.6
Voltage Drop and Regulation. Total voltage drop in a branch
circuit and feeder conductors must not exceed 2 percent from the facility
distribution transformer to the X-ray rooms. Total voltage regulation of
the distribution transformer, feeder, and branch circuit conductors must
not exceed 5%. For circuits which serve only one room, calculations
should be based on the maximum demand current of the single X-ray
generator. For circuits which serve more than one room, calculation
should be based on the maximum demand current of the two largest rooms.
(Calculations should be based on 180 amp maximum demand for 3-phase rooms
and 300 amp maximum demand for single-phase rooms.)
C.2.3.7
Distribution Transformers. Distribution transformers should
not be dedicated solely to X-ray equipment. The voltage regulation is
better if X-ray machines are connected to transformers which are
partially loaded with other equipment. X-ray machines should always be
connected line-to-line, never line-to-neutral.
C.2.3.8
Essential Power. Essential power for X-ray equipment,
illumination, and duplex receptacles shall be in accordance with the
Appendix C - 2
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