Motor Full Load Amps (FLA) Calculator

What Is Full Load Amps (FLA)? Full Load Amps (FLA) is the current an electric motor draws at full rated load and voltage. It is the starting point for sizing conductors, circuit breakers and overload protection, and this calculator estimates it from the motor’s power rating when you do not have a nameplate to hand.

Which FLA number the code actually wants (this catches people out)

There are three FLA figures in play and they are not interchangeable:

• Calculated FLA, what this page produces. A design estimate.
• Nameplate FLA, stamped on the motor and measured for that specific machine.
• Table FLA, from NEC Table 430.248 (single-phase) or 430.250 (three-phase).

NEC 430.6(A)(1) is explicit: conductors, breakers and disconnects must be sized from the table value, not the nameplate and not a calculated one. Overload protection is the exception, and it uses the nameplate figure per 430.32. So treat the conductor and breaker numbers below as a design estimate to check against the table, and set the overload from the nameplate every time.

FLA Formulas Single-phase AC motor: FLA = (HP × 746) / (Voltage × Efficiency × Power Factor) Where 746 W = 1 HP (horsepower to watts conversion).

Three-phase AC motor: FLA = (HP × 746) / (√3 × Voltage × Efficiency × Power Factor) The √3 factor (≈1.732) accounts for the three-phase power relationship.

Typical efficiency for induction motors: 85–95% depending on size. Typical power factor at full load: 0.85–0.90.

NEC Ampacity Rules (US National Electrical Code) The NEC requires specific safety margins for motor circuits: Branch circuit conductors: must be sized for at least 125% of FLA (NEC 430.22). Branch circuit breaker or fuse: up to 250% of FLA for standard breakers (NEC 430.52), or 175% for fuses. Overload protection (motor overloads): set at 115–125% of nameplate FLA to protect the motor windings. Disconnect: must handle at least 115% of FLA and must be within sight of the motor.

Motor Service Factor (SF) The service factor is a multiplier indicating how much beyond rated load the motor can handle continuously. SF = 1.0: motor can only handle rated load. SF = 1.15 (common): motor can handle 115% of rated load for short periods. When SF > 1.0, overloads may be set at 125% of nameplate × SF.

NEMA Motor Nameplate Data Every NEMA (National Electrical Manufacturers Association) motor nameplate includes: HP rating, voltage, FLA, RPM, frame size, insulation class, service factor, efficiency, and power factor. The insulation class (A, B, F, H) defines the maximum allowable winding temperature. Frame sizes (143T, 182T, 213T, etc.) define the mounting dimensions.

Horsepower to kW 1 HP = 0.7457 kW. A 10 HP motor outputs 7.457 kW of mechanical power. Electric power input (kW) = Output (kW) / Efficiency. A 10 HP motor at 90% efficiency draws 8.3 kW of electrical power at full load.

Common Motor Applications HVAC compressors: 1–20 HP, three-phase, 208–230/460V. Pump motors: 0.5–100+ HP. Conveyors: 1–50 HP. Residential HVAC: 0.5–5 HP single-phase, 115–240V. Industrial: almost always three-phase, 460V or 480V, for efficiency.