Control Components
Starters, Pilot Devices, Relays and Timers, Drum Switches, Solid-State Devices and PLCs
Theory from TM 5-683/NAVFAC MO-116 (1995) ch. 5 and 7, Construction Electrician Intermediate (NAVEDTRA 14027) ch. 7, NEETS Modules 1, 3, 7 and 8, all read 2026-09-20 (read-log-neets.md, read-log-theory-manuals.md); NFPA 70-2023 242, 404.14, 409 and 430 as read in read-log-2023.md · Reviewed 2026-09-21
Control hardware — relays, drum switches, magnetic and reduced-voltage starters, overload relays, pilot devices, timers, limit switches, HOA stations, rheostats, rectifiers, regulators, op-amps, surge protectors, PLCs and motion detectors — is General Theory material on the DBPR outline. The control-devices and motor-controller lessons carry the NEC rules for disconnects, controllers, control circuits and industrial control panels; this lesson is the theory of the components themselves, paraphrased from the public-domain Army/Navy manual TM 5-683, the Navy Construction Electrician course and NEETS.
1. The starter and its parts (TM 5-683 5-1, 5-2)
- A starter does more than start: it stops the motor, carries the overload relay, opens the circuit after a period of overcurrent and may add undervoltage, phase-reversal or field-loss protection. A contactor is the coil-and-contacts assembly; a contactor plus an overload relay is a magnetic starter; a magnetic starter plus a breaker or fused switch in the same enclosure is a combination starter, which carries an interrupting rating (breaker-protected, fuse-protected or fused-breaker types; a motor circuit protector, MCP, is magnetic-trip only).
- Manual starter: toggle or pushbutton quick-make/quick-break contacts connect the motor directly to the line — small single-phase fractional-hp motors; has overload protection but no undervoltage protection (it stays "on" through an outage and restarts unattended).
- Magnetic across-the-line starter: the coil closes the line contacts; can be operated from remote pushbuttons or automatically by a float or pressure switch. The starter is not designed to interrupt fault current — the breaker or fuses upstream do that (NEC 430.52); the overload relay handles overloads (430.32). The holding coil drops out when voltage falls to about 60 % of rating — that is the undervoltage protection.
- Contactor care (5-3f): coils run correctly at 85–110 % of rated voltage; low voltage or a blocked armature leaves an air gap, the coil draws excess current and burns out. Replace copper contacts worn thin, dress them
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