DISADVANTAGES OF MANUAL CONTROL OF MACHINES

When electric motors were first introduced, simple manual switches were used to start and stop the motor. The only protective device used was the fuse. Progress was subsequently made along the lines of improving the reliability, flexibility and make-break performance of the manual switches. In those days one large motor was used to drive a line shaft through a belt pulley arrangement. Individual machines were then connected to the line shaft through belt and pulley arrangements. This system of driving a number of individual loads from a common line shaft and manual switching of motors had many disadvantages as listed below:
1) Starting, stopping and speed control of motor had to be performed by hand every time.

2) The operator had to move a manual switching device from one position to another.

3) Switching of large motors required great physical effort.

4) Operator had to remain continuously alert to watch indicators so as to adjust motor performance according to drive requirements.

5) Sequence operations of number of motors could not be accomplished in common line shaft arrangement.

6) The varied needs of individual machines like frequent starts and stops, periodic reversal of direction of rotation, high-starting torque requirement, constant speed, variable speed, etc., could not be accomplished in common line shaft arrangement.