A 4 point starter is used to start and control the speed of a

(A) dc shunt motor with armature resistance control
(B) dc shunt motor with field weakening control
(C) dc series motor
(D) dc compound motor


Answer: option (A)

The armature current of DC shunt motor

Ia = (V- Eb) /Ra.

at the time of starting, Eb = 0. If the full supply voltage is applied to the motor, it will draw a large current due to low armature resistance.
A variable resistance should be connected in series with the armature resistance to limit the starting current.