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starterBy : Anil - 28-Mar-2018 
Difference between a four point starter and three point starter?
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Sankalp29-Mar-2018

Actually both type of starter are used for limiting the starting current of DC motor. NVC (No volt coil) is connected in series with the field coil in 3 point starter whereas NVC is connected across the line in 4 point starter i.e. NVC is in parallel with the field and armature coil.
In 3 point starter whenever the current through field winding decreases while motor is in normal running condition, starter handles comes back to OFF position from RUN position because electromagnetic force produced by NVC becomes weaker than force exerted by spring of starter handle and disconnects the motor from the line.
So to overcome this problem 4 point starter is used. Because in this both circuit NVC and Field coil are independent to each other. Any changes in current in field coil does not affect the NVC and motor keeps on running on normal speed.