Magnetic Primary Resistant Starter

Magnetic Primary Resistant Starter is another method of reducing the starting current of a motor. It is applied to motors with moderate starting current.

Control Operation

Figures 10 (a) and (b) illustrate the power and control circuit respectively of a “Magnetic Primary Resistance Starter”.


Pressing the start push button will energize S contactor, TR timer. Contacts S (13-14) will close to maintain contact circuit. Contact S (1-2,3-4,5-6) will close and complete the circuit in figure 10 (a) from the three supply lines (L1,L2, and L3) down to contact S (1-2,3-4,5-6), O.L. (1-2,3-4,5-6), the 3 resistors R, and finally to the motor M. Motor M will start and reduce voltage since in it is in series 3 resistors R. See simplified illustration in figure 10 (d).

Illustrates the power circuit of the “Magnetic Primary Starter”.

After a few second, the .delay contacts TR (8-6) will closed to energize contactor R coil (A-B). This will close contact R (1-2,3-4.5-6), see figure 10 (a). With contacts R (1-2,3-4,5-6) closed, the 3 resistors R are by pass and the motor M is now connected directly to the 3 lines L1,L2, and L3. See simplified illustration in figure 10 (d).

Illustrates the control  circuit of the “Magnetic Primary Starter”.

Pressing the stop push button will de-energize contactor S and timer TR. Contacts S (13-14) and S (1-2,3-4,5-6)will open. The 3-phrase motor M will stop. Contacts TR (8-6) will open to de-energized contactor R. Contact R (1-2,3-4,5-6) will open to de-energized the contactor R. the circuit condition will bring to the one shown in figures 10 (a) and (b).

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(a) Illustrates the power circuit of the “Magnetic Primary Starter”.
(b) Illustrates the control  circuit of the “Magnetic Primary Starter”.
(c) Motor in series with the 3 resistors at the starting.
(d) Motor directly connected to the supply line when it is already in the stable condition.