Q. Show Typical electric power distribution system?

In central business districts of large urban areas, the primary distribution circuits consist of underground cables which are used to interconnect the distribution transformers in an electric network. With this exception, the primary system is most often radial. However, for additional reliability and backup capability, a loop-radial configuration is frequently used. The main feeder is looped through the load area and brought back to the substation, and the two ends of the loop are connected to the substation by two separate circuit breakers. For normal operation, selected sectionalizing switches are opened so as to form a radial configuration. Under fault conditions, the faulted section is isolated and the rest of the loop is used to supply the unaffected customers.

Most residences and small buildings are supplied with power by means of single-phase, three-wire service, as illustrated in Figure. A distribution transformer is located on a power pole or underground, near the residential customer. Inside residences, the 220-V supply, being available between the two "hot" wires, is used for major appliances such as dryers, ranges, and ovens. The 110-V loads up to 20 to 40 A are connected between the ground wire and either "hot" wire, while nearly balancing the loads on the two "hot" wires. Each of these circuits, protected by its own fuse or circuit breaker, supplies lighting loads and/or convenience outlets. In the wiring of residential and commercial buildings, safety considerations are of paramount importance, the principal hazards being fire and electric shock.