Standard Terminal Markings of DC (Direct Current) Motors

Standard terminal markings, as developed by NEMA, are given for series, shunt and compound motors in figure 1, figure 2 and figure 3 respectively. These figures all show compensating-field as well as commutating-field windings since they are intended to cover both fractional horsepower and integral horsepower motors. Fractional horsepower motors do not generally use compensating windings and they may not use commutating-field (interpole) windings.

The markings are combinations of letters and arabic numerals, generally, these are as follows:

- Armature - A1, A2
- Control signal lead - C
- Series field - S1, S2
- Shunt field - F1, F2

Figure 1: NEMA Standard terminal markings and connections for DC series motors.

Figure 2: NEMA Standard terminal markings and connections for DC shunt motors.

Figure 3: NEMA Standard terminal markings and connections for the compound, or stabilized shunt motors. (a) counter-clockwise rotation; (b) clockwise rotation