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