After cables are carrying the load, inspect all
connections to locate any possible overheating
resulting from poor connections or reduced copper
in the circuit. Inspect cable ends at the point of
connection for heavy strain or overheating.
Shore-power cables are rated at 400 amperes.
Check switchboard meters to ensure that the total
load on shore-power cables does not exceed the
combined rating of shore-power cables. Total
shore-power load in amperes should be no more
than 400 times the number of shore-power, 3-
phase cables connected per phase.
PHASE-SEQUENCE INDICATOR
A phase-sequence indicator is used when you
are connecting shore-power to your ship to ensure
proper phase relationship between ship power and
shore power.
An approved type of phase-sequence indicator
(fig. 3-22) has a miniature, 3-phase induction
motor and three leads with insulated clips
attached to the ends. Each lead is labeled A, B,
and C. The miniature motor can be started by a
momentary contact switch. This switch is mounted
in the insulated case with a switch button
protruding out the front of the case to close the
switch. When the motor starts turning, you can
tell its direction of rotation through the three
ports in the front of the case. Clockwise rotation
would indicate correct phase sequence. You can
stop the motor by releasing the momentary
contact switch button.
UNRIGGING SHORE POWER
When disconnecting shore power, observe
the same safety precautions outlined in the
connecting sequence except for those
regarding meggering cables and checking
phase orientation and phase rotation. Again,
Figure 3-22.-Phase-sequence indicator.
tag shore-power breakers and disconnect following
safety procedures. Determine that the shore-power
busing and cables are de-energized by using a
voltage tester that has just been checked with a
known energized power source.
NOTE: Moving energized shore-power cables
is prohibited.
SUMMARY
In this chapter you have been introduced to the
ac power electrical distributions system. We have
studied the electrical distribution system, bus
transfer switches, ship’s service switchboards, ac
generators,
transformers,
400-Hz
power
distribution, casualty power, and shore power.
Possessing a good understanding of the ac power
distribution within your assigned spaces, will
greatly enhance your ability to restore ac power to
your equipment in the event of its loss or tore-
configure to alternate, casualty, or shore power.
3-18
