Why is it dangerous to supply power to an unloaded series connected dc motors?

Question

Why is it dangerous to supply power to an unloaded series connected dc motors?

Answer 1

In case of DC shunt motors, the starting torque is tremendous, hence the impact or rather the reverse rotational impact tends to damage the assembly if started unloaded, thats why it is dangerous, if loaded the torque is over come by the mass of the load and converts in to momentum

Answer 2

They continue to speed up.  The RPM increases untill the rotor flys apart.  There just ain't nothing to stop it. And it happens really fast!