Precautions while handling DC Series and Shunt motors
A series motor may reach a speed that is too high if it is started without a load. A shunt or separately excited motor can reach an excessive speed if the field becomes disconnected or reduced to a current that is too low.

There may be some difficulty that makes a DC motor undesirable for use with centrifugal pumps or fans. Prior to the availability of electronic speed control, wound-rotor induction motors with rotor resistance speed control were somewhat preferred for those uses. High-slip induction motors with primary voltage speed control were also used.

DC motors rated more that 50 to 100 watts or so need a starting method that limits the starting current. Prior to the availability of electronic speed control, resistors were connected in series with the armature for that purpose. Later, such motors were rarely used without electronic speed control.

For variable speed use, DC motors made need a separately-powered blower for cooling depending of the low-speed duty cycle.