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Option 2 : Series motor
At no load DC series motor rotates at dangerously high speed. Hence dc series motor should always be started on load.
When the motor is connected across the supply mains without load, it draws small current from the supply mains. This current will flow through the series field and armature, the speed tends to increase so that back emf may approach the applied voltage in magnitude.
The increase in back emf weakens the armature current and hence the field current. This cause again increases the speed so the back emf. Thus, the field continues to weaken and speed continues increase until the armature produced such centrifugal force that it is coming out from its shaft and gets damaged.
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