DC Motors
Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control

Four point starter is used
Three point starter is used
Drum type controller is used
All above can be used

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DC Motors
As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit

Armature is temporarily open circuited
A resistance is connected in series with armature
A high value resistor is connected across the field winding
A resistance is connected parallel to the armature

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