Four point starter

•    In 3 point starter the no volt release coil gets connect in series with shunt field winding.

•    When external resistance is included in series with the shunt field winding in order to control the speed of the motor, the field current which is flowing through the no volt release coil decreases.

•    Therefore due to this decreased current, the no volt coil may become so weak as to be unable to keep the handle in on position.

•    This is the main drawback in 3 point starter.

•     In a 4 point starter there are 4 terminals L+, L-, A and F for connecting the dc motor to the supply as shown in the following figure.

•    Here the no volt release coil in series with a protective resistor Rp is connected across the terminals L+, L-.

•    The operation of the four point starter is same as that of 3 point starter except the current through no volt coil depends upon the supply voltage alone.