Primary Mains

Figure 2-6.—Typical pole-mounted feeders, primary mains, transformers, and secondaries. system. It provides the best service reliability to the through fused or automatic cutouts. Figure 2-6 shows distribution transformers or load centers, particularly when the system is supplied from two or more distribution substations. Power can flow from any substation to any distribution transformer or load center in the network system. The network system is more flexible about load growth than the radial or loop system. Service can readily be extended to additional points of usage with relatively small amounts of new construction. The network system, however, requires large quantities of equipment and is, therefore, more expensive than the radial system. Primary Mains Primary mains are connected to the primary feeders. In overhead installations, these mains are always installed below the feeders on a pole. The distribution transformers are connected to the primary mains the primary main to which the transformer is tapped. The cutouts, one on each primary line, contain the fuses that protect the transformer against overload and short circuits. Distribution Transformers 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. 2-4