Intermittent duty (S3)
Duty type under IEC 60034-1 in which identical cycles of operation at constant load and a currentless rest period repeat. Starting does not materially affect heating. More in Duty Types S1, S2 and S3.
Brushed motor
DC motor in which carbon brushes mechanically transfer current via a commutator to the rotating armature. Compared with the brushless design in Brushed or Brushless Motor?.
Brushless motor
Motor in which commutation is electronic instead of via mechanical brushes and a commutator - wear-free, but dependent on drive electronics. Details in Brushed or Brushless Motor?.
Continuous duty (S1)
Duty type under IEC 60034-1 in which the motor runs at constant load long enough to reach thermal equilibrium - the typical rating for continuously running pumps, fans or production equipment. More in Duty Types S1, S2 and S3.
Torque
The force acting on the motor shaft multiplied by the lever arm. Together with speed, torque determines a motor's delivered mechanical power and is a key sizing parameter.
Cyclic duration factor (CDF)
Percentage share of operating time in the sum of operating and rest time within one load cycle - a key parameter for intermittent and short-time duty. The Duty Types S1-S3 article's underlying model lets you work through the CDF directly.
Separately excited motor
DC motor in which field and armature windings are supplied separately. This allows a wide control range and a flexible characteristic curve. Compared with the other designs in DC Motor Types Compared.
IP rating
Classification under IEC 60529 stating the degree of protection of an enclosure: the first digit (0-6) describes protection against solid objects and dust, the second (0-9K) against water - for example IP54 for dust-protected and splash-proof.
Insulation class (thermal class)
Classification of insulating materials under IEC 60085 by their permissible limit temperature, including class B (130 degrees C), F (155 degrees C) and H (180 degrees C). Class F is today's common standard for electric motors.
Commutator
Mechanical current switch on the armature shaft of a brushed motor, contacted via carbon brushes, which reverses the armature current at the right moment so the armature keeps turning continuously. More in Brushed or Brushless Motor?.
Short-time duty (S2)
Duty type under IEC 60034-1 in which the motor runs at constant load for a defined time, followed by a rest period until it cools down completely. More in Duty Types S1, S2 and S3.
Shunt motor
DC motor in which field and armature windings are connected in parallel across the same supply. This gives a relatively constant speed under changing load. Compared in DC Motor Types Compared.
Permanent-magnet motor
DC motor whose field is produced by permanent magnets instead of a field winding - compact, with no excitation current required, and efficient at low to medium power. Details in DC Motor Types Compared.
Series-wound motor
DC motor in which field and armature windings are connected in series. This delivers very high starting torque but makes the motor load-dependent - running it without a suitable load can let speed rise to a dangerous level. More in DC Motor Types Compared.
Thermal time constant
Parameter describing how quickly a motor heats up or cools down after a load change. It is decisive for assessing intermittent and short-time duty.
Efficiency
Ratio of delivered mechanical power to consumed electrical power of a motor. The difference is lost as heat and, alongside sizing, determines energy consumption in operation.
Sources (selection): IEC 60034-1 (duty types), IEC 60085 (insulation classes), IEC 60529 (IP ratings).