Electrical Equipment, Devices, and Controls
Core concepts
Understand switchgear, panelboards, transformers, motors and controllers, receptacles, switches, and protective devices. Know overcurrent device types (fuses, molded-case breakers), interrupting rating, series ratings, and coordination. Motor circuits require overload protection (separate from branch-circuit short-circuit protection) and controllers per Article 430. Transformers require primary and secondary protection per Article 450. Controls include contactors, relays, starters, VFDs, and pilot devices; know basic ladder logic and two-wire versus three-wire control.
Traps
Questions confuse overload protection with short-circuit/ground-fault protection-overloads protect the motor, branch protection protects the circuit. Remember that a disconnect must be within sight and readily accessible. Series-rated breakers must be listed as a combination. VFDs can create harmonics and require shielded cable and proper grounding. Watch for the difference between a receptacle's rating and the circuit's rating.
Worked example
A 10 HP, 460 V three-phase motor: Table 430.250 gives 14 A FLC. Branch-circuit short-circuit protection (inverse-time breaker) may be sized up to 250% of FLC = 35 A; overload protection is sized to the motor's nameplate service factor and typically set near 115–125% of FLC.
Rule of thumb
Motor questions: find FLC from the Code table first, then apply the percentage rules for branch protection and overloads separately.