Motor Fla Calculator

Motor Full Load Amps (FLA) Calculator

Horsepower (HP) Kilowatts (kW)

Three-Phase (3φ) Single-Phase (1φ)

Estimated Full Load Current: 0.00 Amps

What is Motor Full Load Amps (FLA)?

Motor Full Load Amps (FLA) represents the amount of current a motor will draw when it is operating at its rated horsepower, rated voltage, and rated frequency. This value is critical for electrical engineers and electricians when sizing wire gauges, circuit breakers, and motor overload protection devices.

Understanding the Variables

• Power Rating: Usually given in Horsepower (HP) or Kilowatts (kW). 1 HP is roughly equivalent to 746 Watts.
• Voltage: The supply voltage. Common industrial voltages include 208V, 230V, 460V, or 575V.
• Phase: Industrial motors are typically 3-phase, while residential or small commercial motors are often 1-phase.
• Efficiency: No motor is 100% efficient. This accounts for energy lost as heat or friction.
• Power Factor: The ratio of real power to apparent power. AC motors are inductive loads, typically having a power factor between 0.70 and 0.90.

The Calculation Formulas

The math behind FLA changes based on the phase configuration:

Single Phase (1φ): Amps = (Power in Watts) / (Voltage × Efficiency × Power Factor)

Three Phase (3φ): Amps = (Power in Watts) / (Voltage × 1.732 × Efficiency × Power Factor)

Calculation Example

Suppose you have a 5 HP three-phase motor running at 460V with an efficiency of 88% and a power factor of 0.82:

1. Convert HP to Watts: 5 × 746 = 3,730 Watts.
2. Calculate the denominator: 460 × 1.732 × 0.88 × 0.82 = 575.29.
3. Calculate FLA: 3,730 / 575.29 = 6.48 Amps.

Note: This calculator provides theoretical values. Always refer to the motor's nameplate and the National Electrical Code (NEC) tables (like Table 430.250) for official sizing and safety compliance.

function calculateFLA() { var motorPower = parseFloat(document.getElementById('motorPower').value); var powerUnit = document.getElementById('powerUnit').value; var voltage = parseFloat(document.getElementById('voltage').value); var phase = parseInt(document.getElementById('phase').value); var efficiency = parseFloat(document.getElementById('efficiency').value) / 100; var powerFactor = parseFloat(document.getElementById('powerFactor').value); var resultDiv = document.getElementById('flaResult'); var ampValueSpan = document.getElementById('ampValue'); if (isNaN(motorPower) || isNaN(voltage) || isNaN(efficiency) || isNaN(powerFactor) || voltage <= 0 || efficiency <= 0 || powerFactor <= 0) { alert('Please enter valid positive numbers for all fields.'); return; } // Convert to Watts var watts; if (powerUnit === 'HP') { watts = motorPower * 746; } else { watts = motorPower * 1000; } var fla = 0; if (phase === 3) { // 3-Phase Formula: Watts / (V * sqrt(3) * Eff * PF) fla = watts / (voltage * 1.73205 * efficiency * powerFactor); } else { // 1-Phase Formula: Watts / (V * Eff * PF) fla = watts / (voltage * efficiency * powerFactor); } ampValueSpan.innerText = fla.toFixed(2) + ' Amps'; resultDiv.style.display = 'block'; resultDiv.style.backgroundColor = '#e8f5e9'; resultDiv.style.border = '1px solid #c8e6c9'; }