What is the difference between a four point starter and three point starter?

The shunt connection in four point starter is provided separately form the line where as in three point starter it is connected with line which is the drawback in three point starter.

In three point starter NVR (no voltage relay) is series with shunt if voltage falls certain value NVR De energized due to insufficient magnetic field and motor turned off. But in four point starter NVR energized directly from DC supply thus the draw back of 3 point starter rectified.

The basic difference in 3 point starter and 4 point starter is in the connection of NVC(No volt coil).
In a 3 point starter the NVC is connected in series with the field winding.
And in a 4 point starter the NVC is connected to the 4rth coil.