What is a characteristic danger of a series motor when running without a load?

When a series motor operates without a load, a notable danger is the risk of overspeeding. This occurs because the torque produced by the motor is directly related to the load it carries. In a series motor, the field winding is connected in series with the armature, meaning that the current flowing through the armature also flows through the field winding. When there is no load, the current is low, leading to a weaker magnetic field.

As the load decreases, the motor accelerates, and since there is less opposition from the field winding due to a reduced magnetic field, the armature speed increases uncontrollably. If this condition persists, the motor can reach speeds far beyond its design limits, potentially resulting in mechanical failure or damage to the motor components due to centrifugal forces. Therefore, the characteristic danger of a series motor running without load is indeed overspeed, as this can lead to hazardous operating conditions.