Motor Types and Connections
DC Series, Shunt and Compound Motors; Single-Phase and Three-Phase AC Motors; Reversing, Speed, Dual-Voltage and Delta/Wye Stator Connections
Theory from NEETS Module 5 (NAVEDTRA 14177A) chapters 2–4 read 2026-09-20 (read-log-neets.md); code references to NFPA 70-2023 Article 430 as read in read-log-2023.md · Reviewed 2026-09-21
The PSI "Rotating Equipment" list (9 items Class I, 16 items Class II) is written as shop tasks: change the rotation of a motor, change the speed of a single-phase motor, connect a motor to run on a different voltage, connect a three-phase stator for delta or for star (wye), and install or replace each named motor type. Article 430 (lesson nec-07-01) tells you how to protect and wire the circuit; this lesson is the machine itself. The theory paraphrases the public-domain Navy NEETS course, Module 5.
1. DC motors — series, shunt, compound (NEETS 2.5)
| Type | Field connection | Torque and speed behaviour | Typical use |
|---|---|---|---|
| Series | field in series with the armature — few turns of heavy wire carrying full armature current | very high starting torque; speed varies widely with load; races to destruction with no load — always keep a load connected | hoists, cranes, winches, traction, portable tools (as the universal motor) |
| Shunt | field in parallel with the armature — many turns of fine wire on constant voltage | nearly constant speed under changing load (constant field flux; counter emf self-regulates armature current); moderate starting torque | machine tools, fans, pumps needing steady speed |
| Compound | both a shunt field and a series field ("long shunt" when the shunt field spans series field plus armature; "short shunt" otherwise) | shunt-motor speed stability plus series-motor starting torque under heavy load | compressors, elevators, punch presses — loads that start heavy and then run steady |
- Counter emf: a running armature generates a voltage opposing the supply; armature current = (supply − counter emf) ÷ armature resistance. At standstill there is no counter emf and armature resistance is tiny (tenths of an ohm or less), so a starting resistance is put in series with the armature until the counter emf builds up (NEETS 2.10).
- Reversing a DC motor (NEETS 2.7): rotation depends on the direction of the field and the direction of the armature current. Reverse either the field connections or the armature connections — never both (reversing bot
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