In this topic, you study 4 Point Starter (Four Point Starter) – Working, Diagram & Construction.
This type of starter is similar to a three point starter except that the hold-on coil along with its protective resistance R’ is connected across the supply line instead of in series with the shunt field circuit and thus have four points L1, L2, A, F as shown in Fig. 1.
Fig. 1: Four-point starter for a dc shunt motor
This arrangement permits variation of motor speed with the help of a field regulator Rf without affecting the current through the hold-on coil. The disadvantage of this type of starter is that the hold-on coil being independent of field circuit connection, no protection is provided against over speed if for some reason field circuit is open circuited. It is important to note here that the three-point and four-point starters described above are also used for starting dc compound motors.