The nameplate ratings of a DC motor refer to the conditions of voltage, current, speed, and power at which the motor is normally operated. The principal rating is known as the continuous rating, which is the rating described on the nameplate of a motor. The continuous power rating is a thermal rating. At this power, the motor can be operated for long periods of time without a large rise in temperature and beyond the limits of the conductor insulating material, bearings and other components, which are greatly affected by temperature.

The speed rating of a DC motor is often given on the nameplate. This speed is the upper limit at which a motor can be operated without mechanical damage occurring.

Summary

DC motor operation is summarized below.

DC Motor Operation Summary

Starting resistors are necessary for large DC motors to prevent damage due to high currents while starting the motor.

Starting resistors are placed in the starting circuits for the controllers that start the motor. When the motor reaches full speed, the starting resistors are cut out of the circuit.

The four nameplate ratings for a DC motor include:

voltage current speed power