Purpose. The purpose of a schematic diagram is to make it possible to picture the operation of an entire control circuit for a piece of equipment, so that it will be easy to think in terms of an entire circuit instead of a particular component part of it. Once the control schematic diagram is understood, it is easy to apply the information contained on it to some portion of the associated wiring diagram.

Feeder Circuit Control Schematic. The control schematic diagram for a distribution substation feeder circuit breaker installed in a metal-clad switchgear unit (Fig. 39.1) is traced by utilizing the numbers appearing by the component parts of equipment. Each piece of equipment and the purpose it serves are described.

The schematic diagram of Fig. 39.1 is drawn for the condition of all isolating devices open and the circuit breaker in the open position. This is an accepted standard method of drawing schematic control diagrams. The symbol < < represents a circuit breaker draw-out contact in the switchgear. All equipment shown between the draw-out contacts is located on the feeder circuit breaker.

The control source for closing the feeder circuit breaker is 240 volts alternating current. The lead designations for the control power source are X1 and Y1. Starting with wire X1, a circuit extends to item (1), a knife switch which isolates and deenergizes the control circuit. From the knife switch, the circuit is completed to item (2), which is a low-voltage fuse used for isolating the...