Most electrical equipment in the Navy uses 120/208 volts. The primary voltage on Navy shore installations, however, is usually 2,400/4, 160 volts. For this reason, a distribution transformer is required to reduce (step down) the high primary voltage to the utilization voltage of 120/208 volts. Figure 2-6 shows one of various different types of transformer arrangements and installations. Regardless of the type of installation or arrangement, transformers must be protected by fuses or circuit breakers and lightning protection. transformer. It requires no separate protective devices.

Secondary mains or circuits are the lines that carry the electric power from the secondary side of the transformer through a distribution system to supply the electrical loads. They may or may not be on the same pole with the feeder lines. If on the same pole, they may be either on a crossarm below the feeder lines or, as shown in figure 2-6, on spool racks attached to the side of the pole below the feeder lines. The secondary circuits may have several wires (service drops) connected to various buildings to serve their electrical needs. Where a large load is in demand, a transformer or transformer bank may be located at the building site.

SINGLE PHASE. Single-phase secondary circuits usually supply current for electrical lighting loads, small electric appliances, and small (1 horse-power and under) single-phase electric motors. The secondaries consist of two hot conductors and one neutral conductor. In overhead construction, these conductors are mounted on the bottom crossarm on a pole or on spools attached to the side of a pole. (See fig. 2-6.) One transformer will feed this circuit if the required load to be served is not too heavy. Where the load is heavy or where several buildings are served, a bank of three transformers may feed the circuit. The normal voltage of a single-phase circuit is 120 volts from either one of the energized conductors to the neutral or 240 volts across the two energized conductors.

THREE PHASE. Some facilities, such as motor pools, industrial shops, and water and sewage plants, may have equipment using three-phase motors, which require three-phase power. Transformer banks are installed to supply this power. If a number of buildings in the area require three-phase power, cluster mount may be installed with the three-phase secondaries extending in two or three directions and with service drops extending from the secondary to the buildings.

As you learned in the EA3 TRAMAN, each building requiring electric current must have lead-in conductors, known as service drops. These may be current to one load only.