Since Enginemen and Electricians Mates are assigned duties in operating diesel-driven emergency generating plants on steam-driven ships, and all electrical generating plants on diesel-driven ships, they must have a general knowledge of the purpose of electric generating plants, their opera-tion under various conditions, and the types of casualties that will interfere with, or disrupt, the normal operation of an engineering plant.

THE ELECTRICAL PLANT

The ships power and lighting plant consists of generators, switchboards, power panels, cables, circuit breakers, and other equipment necessary for the generation, distribution, and control of power supplies to electrically driven auxiliaries, lighting, interior communication, electronics equipment, and other electrically powered devices. In designing the electric plant, every effort is made to obtain the greatest reliability and continuity of service possible under casualty conditions. The distribution system forms the vital connection between the generators and the equipment which uses electric power. The distribution of electrical power is generally done through either the ships service or the emergency switchboards. Electrical power distribution may also be done through a casualty power circuit rigged from either of these switchboards.

The general arrangement of the ships service system is such that any faulty circuit will be cut out automatically, without interruption of power supply to other circuits. This is done through the operation of protective devices. If the ships service generators fail, the emergency generator is automatically placed in operation for battle functions. The emergency switchboard can supply power to all parts of the ship; however, all un-necessary circuits must be stripped from the board when the emergency generator is set up in automatic to supply emergency power to vital equipment. If this is not done, the generator will be overloaded and the breakers will trip out or the diesel engine will stall.

Protection against loss of power on a ship with ships service, emergency, and casualty power distribution systems is described below:

1. FAILURE OF ONE SHIPS SERVICE GENERATING PLANT. The load is transferred, by the Electricians Mate, to the other ships service generating plant. Care must be taken to prevent overloading the generating plant that takes over the load.

2. CIRCUIT OR SWITCHBOARD FAILURE. Vital loads are transferred to an alternate feeder and source of ships service power by means of a transfer switch on the control panel.

3. FAILURE OF BOTH NORMAL AND ALTERNATE POWER SUPPLY. Certain vital equipment are shifted to an emergency feeder which receives power from the emergency switchboard.

4. FAILURE OF THE SHIPS SERVICE AND EMERGENCY CIRCUITS. Temporary circuits are rigged with the casualty power cables from any live switchboard to supply power to vital circuits.