Motors, Motor Controls, and HVAC Equipment
Motor questions mix tables and nameplates, and the exam expects you to know which governs.
The core sequence
Motor full-load current usually comes from the Code tables based on horsepower and voltage, not from the nameplate-except for certain hermetic refrigerant motor-compressors, where the nameplate rated-load current governs. Branch-circuit conductors are sized at 125 percent of the motor full-load current. The branch-circuit short-circuit and ground-fault protective device is sized from the Code table for the motor type and may be increased to the next standard size to allow starting. Running overload protection is separate, sized from the full-load current and selected so the motor is protected without nuisance tripping.
Controls and disconnecting means
A disconnecting means must be within sight of and readily accessible from the motor, with exceptions only where the Code permits a lockable remote disconnect. The controller (starter) provides starting and stopping; the disconnect provides isolation. Control circuits, emergency stops, and undervoltage protection each have their own rules. For HVAC equipment, the nameplate minimum circuit ampacity and maximum overcurrent protection govern the supply conductors and the breaker; you size to the nameplate, not by calculation.
Traps
Using nameplate amps where the table applies; using table amps for a hermetic compressor; installing a breaker larger than the nameplate maximum; omitting overload protection because the breaker "protects the motor"; and locating the disconnect out of sight.
Rule of thumb
Motor: table current × 1.25 for conductors. HVAC unit: build to the nameplate minimum circuit ampacity and maximum fuse or breaker size.