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## Learning Task 2 ### Three-Wire Circuits The ON/OFF switch can be replaced with a float switch, pressure switch, or temperature switch. Figure 3 shows a simple three-wire control circuit with a momentary-contact, STOP/START push-button station. The STOP button is normally closed and opens when...

## Learning Task 2 ### Three-Wire Circuits The ON/OFF switch can be replaced with a float switch, pressure switch, or temperature switch. Figure 3 shows a simple three-wire control circuit with a momentary-contact, STOP/START push-button station. The STOP button is normally closed and opens when depressed. The START button is normally open (n.o.) and closes when depressed. When released, both actions revert to their normal state. * When the START button is pressed, the coil is energized. This closes the main power contacts and the seal-in contact. * When the START button is released, current to the coil is maintained through the closed *seal in contact*. The coil stays energized and the motor continues to run. * If there is an overload on the motor, the opening of the n.c. OLR contacts in the control circuit de-energizes the coil and stops the motor. * When the STOP button is depressed, a similar action is obtained, with all magnetic starter contacts falling open. * If there is a power failure during normal running, the magnetic starter coil becomes de-energized and all starter contacts open. When power is restored, the control circuit must be manually restarted. This is called *under-voltage protection*. ### Pilot Lights A pilot light is sometimes used to indicate the operating status of a motor in a remote location. Figure 4 shows the electrical connections for an ON light in the control circuit. Note that it is connected in parallel with the coil of the magnetic starter. Whenever the coil of the starter is energized, the pilot light is also energized.