BUS TRANSFER SWITCHES

CREW LIVING SPACE, FRAMES XX - XX FIRST PLATFORM LIGHTING PANEL 4-108-2 2S-4L-(4-103-2) If a panel contains two or more sets of buses and each set is supplied by a separate feeder, the number of each feeder will be indicated on the identification plate. Distribution panels have circuit information plates next to the handle of each circuit breaker or switch. These plates contain the following information in the order listed: 1. The circuit number. 2. The name of the apparatus or circuit controlled. 3. The location of the apparatus or space served. 4. The circuit breaker element or fuse rating. Vital circuits are shown by red markers attached to circuit information plates. Information plates for circuit breakers supplying circle W and circle Z class ventilation systems contain, in addition to the red marker, the class designation of the ventilation system supplied. Information plates without markings are provided for spare circuit breakers mounted in distribution panels. Panel switches controlling circuits that are de-energized during darkened ship operations are marked DARKENED SHIP. The ON and OFF position of these switches are marked LIGHT SHIP and DARKENED SHIP, respectively. Circuit information plates are provided inside fuse boxes (next to each set of the fuses). They show the circuit controlled, the phases or polarity, and the ampere rating of the fuse. PHASE SEQUENCE The phase sequence in naval ships is ABC; that is, the maximum positive voltages on the three phases are reached in the order A, B, and C (fig. 3-3). Phase sequence determines the direction of rotation of three-phase motors. Therefore, a reversal of the phase sequence could cause damage to loads, especially pumps, driven by three-phase motors. The phase sequence of the power supply throughout a ship is always ABC (regardless of whether power is supplied from any of the switchboards or from the shore power connection) to ensure that three-phase, ac motors will always run in the correct direction. Figure 3-3.-Sine curve for three-phase circuit. Phase identification is denoted by the letters A, B, and C in a three-phase system. Switchboard and distribution panel bus bars and terminals on the back of switchboards are marked to identify the phase with the appropriate letters, A, B, or C. The standard arrangement of phases in power and lighting switchboards, distribution panels, feeder distribution boxes, feeder junction boxes, and feeder connection boxes is in the order A, B, and C from top to bottom, front to back or right to left when facing the front of the switchboard, panel, or box, and left to right when facing the rear of the switchboard, panel, or box. BUS TRANSFER SWITCHES Bus transfer equipment is used to provide two sources of power to equipment that is vital to the ship. This vital equipment is that equipment needed to operate safely or could cause the ship to become disabled if it becomes de-energized. Depending upon the application, the transfer from one source to another may be done manually, by a manual bus transfer switch, or automatically by an automatic bus transfer switch. MANUAL BUS TRANSFER (MBT) SWITCHES When normal power to vital equipment is lost, power must be restored as soon as possible to ensure the safety of the ship. MBTs maybe used to switch from normal to alternate or emergency power for those loads that draw a large starting current or for which some condition must be met before energizing. A good example of this would be HF radio equipment, if power would be automatically reapplied after a sudden loss, major damage would occur to the transmitter. 3-3