What is Motor Circuits?

Before learning about the motor starter circuits, first we learn about some important devices, which are used in motor starter circuits. Starter consists of a magnetic contactor, thermal relay, push buttons, light indicators and some time we use fuses or circuit breakers inside the starter, but his condition is rarely used .
A motor is rated in horse power (H.P). This means that is will deliver the horse power stamped on its name plate. Motors deliver far  more power while starting than after they are up-to full speed. The proportion varies with the type of motor, some types have starting torques 4 or 5 times greater than at full speed.
Naturally, the watts consumed during the starting period are much higher than while the motor is running at full speed.. That means the motor will heat up quickly, if it does not reach full speed because of too heavy starting load.
Remember these important points, when you make the connections of a sub-circuit of the motor.

(A) Always use the fuses or circuit breaker in sub-circuit of the motor.

(B) Always use the start and stop buttons in motor circuit, a controller is also used, because it insolates the motor from supply. In motor starter circuits relays must be used because it protects the circuit against overloading. A under voltage protection is also used with motor circuit.

(C) The value of volt-drop is not exceeding to 5% in controlling and protecting devices and cables of the motor.

(D) The rating of the final sub circuit is 15A. We can also derive the more than one motor on the final sub-circuit but the total load of the motor always remains less than 15A.

(E) The Motors, whose current ratings are greater than 20 or equal to 20, are always derive with distribution fuse board, where fuses and circuit breaker are installed.

A motor circuit is shown in below diagram. In this circuit three blocks are shown, in first block sub-circuit protection is marked, in second isolator is marked and in third starteris marked.