Power is used by any equipment that requires electrical power for its operation (lights, motors,
director power drives, radar equipment, weapon direction equipment, computers, etc.). The maintenance
of the ship service generators, the emergency generators, and distribution switchboards is the
responsibility of the ship's engineers (machinist's mates, electrician's mates, enginemen, etc.).
If power from the ship service distribution system is interrupted, the emergency power distribution
system is activated. The emergency system supplies an immediate and automatic source of electrical
power to selected loads that are vital to the safety and defense of the ship. This system includes one or
more emergency diesel generators and switchboards. The emergency generator is started automatically
when a sensor detects the loss of normal power.
Bus Transfer Equipment
Bus transfer equipment is installed on switchboards, at load centers, on power panels, and on loads
that are fed by both normal and alternate and/or emergency feeders (figure 4-11). Either the normal or
alternate source of the ship's service power can be selected. Emergency power from the emergency
distribution system can be used if an emergency feeder is also provided.
Automatic bus transfer (ABT) equipment is used to provide power to vital loads, while nonvital
loads can be fed through manual bus transfer (MBT) equipment. For example, the interior
communications (IC) switchboard is fed through an ABT in which the alternate input is from the
emergency switchboard. A search radar might be fed through an MBT.
Many other supply voltages are used in radar systems and subsystems. They are usually used as
reference voltages for specific functions. When you are missing a power input to your equipment, work
backwards from the load to the source. Usually, the power panels and bus transfer units that feed the
equipment are located nearby, possibly in the same space or in a passageway.
Keep in mind that technicians have corrected many suspected casualties merely by restoring a minor
power input or signal reference, sometimes after hours of troubleshooting.
Q12. Most shipboard distribution systems use ac power that has what number of phases?
Q13. How is emergency power applied when normal power is lost?
Q14. What device is used to switch power from the normal source to an alternate source for nonvital
Q15. What procedure should you use when a power input to your equipment is missing?
Some radars depend on inputs of dry air for proper operation. Radar dry air is normally supplied by
the ship's central dry-air system. This system produces high-pressure (hp) air and low-pressure (lp) dry air
for distribution to user equipment, such as a search or a fire control radar.
Electronics Dry-Air Branch
The electronics dry-air branch is fed from the vital service lp air main through the Type II (desiccant)
or Type III (combination refrigerant and desiccant) dehydrators, as shown in figure 4-12. The purpose of