PHASE-SEQUENCE INDICATOR

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