About this calculator
This calculator provides a quick electrical sizing package from motor horsepower and voltage — full load amps from the motor formula, MCA at 125% of FLA, MOCP at 225% of FLA with the standard breaker it allows (the same results as the MCA and MOCP calculators), and the recommended copper wire size for the MCA. Use it as a first pass when specifying electrical requirements for HVAC equipment. For code conductor sizing, NEC Table 430.250 FLA values should be used instead of the formula.
Use when You need a complete electrical sizing calculation from motor horsepower and voltage.
Formula FLA = (HP × 746) ÷ (V × √3 × Eff × PF), with √3 = 1 for single-phase
Variables
Horsepower Motor horsepowerVoltage System voltagePhase Single or three phaseEfficiency Motor efficiency as a percentagePower Factor Motor power factor as a percentage
Horsepower (HP)
Motor rated horsepower
Voltage (V)
Supply voltage
Phase
Single (1) or three (3) phase
Efficiency (%)
Motor efficiency percentage
Power Factor (%)
Motor power factor percentage
FLA —
MCA —
MOCP —
Standard Breaker —
Wire Size —

How is motor full-load amperage calculated?

Motor full-load amperage (FLA) is the current drawn by a motor operating at rated horsepower and voltage under full mechanical load. For three-phase motors, FLA is calculated as: FLA = (HP × 746) ÷ (Voltage × √3 × Efficiency × Power Factor), where 746 converts horsepower to watts, √3 (1.732) accounts for three-phase power, and Efficiency and Power Factor are expressed as decimals. For single-phase motors, the √3 factor is omitted. NEC Table 430.250 provides standard FLA values for three-phase motors that are used for circuit sizing regardless of the actual nameplate current; this calculator uses the formula, so its FLA can differ from the table value. The FLA is the starting point for determining MCA, overcurrent protection, and wire size for the motor circuit.

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