Amperage Calculator - HVAC Calculator Toolbox

About this calculator This calculator provides a complete electrical sizing package from motor horsepower and voltage — full load amps, MCA, MOCP, and recommended wire size. Use it as a single-step solution when specifying electrical requirements for HVAC equipment submittals. The calculation follows NEC Articles 430 and 440 for motor and HVAC equipment circuits.

Use when You need a complete electrical sizing calculation from motor horsepower and voltage.

Formula FLA = (HP × 746) ÷ (V × √Phase × Eff × PF)

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

Three Phase

Phase

Single (1) or three (3) phase

Efficiency (%)

Motor efficiency percentage

Power Factor (%)

Motor power factor percentage

FLA —

MCA —

MOCP —

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. The calculated or table FLA is the starting point for determining MCA, MOCP, and wire size for the motor circuit. In HVAC applications, the equipment nameplate FLA reflects the combined electrical load of all motors and controls within the unit, which is typically higher than the individual motor FLA.

Related Calculators