NEC 430 Motors and Controllers: Overload vs Short-Circuit Protection

Regulation: NEC Article 430

Keywords: NEC 430 motors, motor overload protection, short-circuit protection motors, motor branch circuit, controller NEC, motor disconnect, inverse time breaker motor, motor FLA nameplate

Core Concepts

• Overload Protection: Protects motor windings from sustained overcurrent due to mechanical overload. Sized at 115–125% of motor FLA per nameplate. Trips slowly to allow motor inrush.
• Short-Circuit and Ground-Fault Protection: Protects branch circuit conductors and motor from faults. Sized much higher: up to 250% for inverse time breakers, 175% for dual-element fuses. Trips fast.
• Branch Circuit Conductor Sizing: Motor branch circuit conductors must be rated at least 125% of motor FLA — not the overload device rating.
• Controller: Must be capable of interrupting the stalled-rotor current of the motor. A general-purpose snap switch is acceptable only for small motors under specific conditions.

Exam Traps

• Overload protection and short-circuit protection are two separate devices with separate sizing rules — they are not interchangeable.
• The overload device is sized from the motor nameplate FLA, not NEC Table 430.248/250 values (those are used for conductor and disconnect sizing when nameplate is unavailable).
• A single device can serve as both overload and short-circuit protection only if listed for that combined purpose.
• Hermetic refrigerant motor-compressors (Article 440) have different sizing rules — do not apply Article 430 percentages directly.
• The disconnecting means must be within sight of the controller AND within sight of the motor unless specific exceptions apply.

Memory Aid

Two separate layers: OVERLOAD = slow, protects motor windings, sized ~125% FLA. SHORT-CIRCUIT = fast, protects conductors, sized up to 250% FLA.