What will happen whn field supply of DC motor is

Howdy,

You lose the field magnetism and the motor will no longer turn. And when this happens, you get no rotation of the armature, hence, no alternating connections (through the commutator) of the armature windings which could cause them to burn up and ultimately throw a breaker of blow a fuse. Or start a fire in the worse case, from overheating. Not a good scenario.

Good luck,

J