Full Load Amperage (FLA) is the continuous electrical current a motor draws when operating at its nameplate horsepower rating under normal load conditions. FLA is the fundamental specification for sizing motor controls, overload relays, branch circuit breakers, and electrical conductors in HVAC systems.
Specifications and Standards
FLA values are stamped on motor nameplates and comply with NEMA MG-1 standards. FLA varies with motor voltage, efficiency rating, and frame size. A typical 3 HP, 208V three-phase motor draws approximately 8.7 amps FLA, while a 10 HP equivalent draws 28 amps. FLA increases as voltage decreases for the same horsepower. Dual-voltage motors have different FLA ratings for each voltage option, typically lower current at higher voltage.
Electrical Conductor and Breaker Sizing
Branch circuit conductors must be sized at minimum 125% of motor FLA per National Electrical Code Article 430. A 28-amp FLA motor requires conductors rated for 35 amps minimum. Breaker sizing requires 250% of FLA for instantaneous trip breakers, or 225% for inverse-time breakers. Overload relays are set at 115-125% of FLA to provide protection without nuisance tripping during normal operation.
System Balance
Comparing nameplate FLA to actual operating current verifies motor health and load conditions. Higher-than-rated current suggests inadequate cooling or mechanical binding. Lower current indicates reduced load or efficiency loss. FLA is essential reference data for all HVAC electrical system design and troubleshooting activities.