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NEC Article 430 covers the installation of motors, motor circuits, and controllers, providing requirements for branch circuits, short-circuit/ground-fault protection, overload protection, and disconnecting means. It features 14 parts (430.1–430.120) designed for specialized motor inrush currents.
Key Components and Requirements Conductor Sizing: Branch circuit conductors must have an ampacity of at least 125% of the motor’s full-load current (FLC). Overload Protection: Motors must have protection against burnout due to overload, typically sized at 115%–125% of the motor’s nameplate full-load ampere (FLA) rating. Short-Circuit/Ground-Fault Protection: Part IV (430.51–430.58) requires branch circuit short-circuit and ground-fault protective devices (e.g., fuses or breakers) sized to handle startup inrush, often up to 250% of the FLC. Disconnecting Means: A disconnecting switch must be located within sight from the controller, and in some cases, the motor. Controllers (Part VII): Controllers must be able to start/stop the motor and interrupt the locked-rotor current. The controller's horsepower rating must be equal to or greater than the motor's horsepower.
Important Design Details FLC vs. Nameplate FLA: Use NEC Tables 430.250 (3-phase) or 430.248 (1-phase) for calculating conductor and protection sizing rather than the motor nameplate FLA. Controller Requirements: Motor controllers must be marked with the maker's name, voltage, and horsepower rating. Motor Control Centers (MCCs): Covered under Article 430, defining the integration of multiple controllers and overcurrent protection in industrial settings.
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