Motors, HVAC, and Industrial Equipment
Motor Circuit Components
Motor circuits have three distinct protections: overload (protects the motor), branch-circuit short-circuit and ground-fault protection, and the controller/disconnect. Questions test whether you can identify which device does what. A common trap is confusing overload protection with short-circuit protection.
Sizing from Tables
Use the motor tables for full-load current based on horsepower and voltage. Branch-circuit conductors are sized at 125% of FLC; the branch-circuit protective device is sized per the motor tables, often permitting a larger device than the conductor ampacity. The overload device is sized from the nameplate or tables per the applicable percentage.
Disconnects and Controllers
A disconnecting means must be within sight of the motor and controller in most cases, and the controller must be readily accessible. HVAC equipment follows Article 440, which has its own rules for hermetic refrigerant motor-compressors, including the branch-circuit selection current and the marked maximum overcurrent device.
Industrial Equipment
Industrial machinery, cranes, and welders have dedicated articles. Focus on the requirement to follow the equipment's listing and nameplate markings, which often override general rules.
Worked Example
A 10 hp, 230 V, three-phase motor has an FLC from the table of about 28 A. Branch-circuit conductors are sized at 125% (35 A), while the short-circuit device is sized from the motor table, which may allow a larger breaker. If an answer sizes the overload at 125% of FLC, that is a distractor-overloads use a different basis.