Difference between 3 point starter and 4 point starter?

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

starter

2.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