Generator Breaker Size Calculator

Determine the correct circuit breaker size for your generator

Generator Breaker Size Calculator

Compliant with NEC Standards

Results:

Full Load Amps (FLA): 0.00 A

Recommended Breaker Amps: 0.00 A

Round up to the nearest standard breaker size.

Generator kVA to Amps Calculator
Generator Amps Calculator

How to Use the Calculator

Input Generator Details

  1. Select "kVA" or "kW" for power unit.
  2. Enter the generator's power rating.
  3. Input the generator's output voltage.
  4. Choose the phase (Single or Three Phase).
  5. If "kW" is selected, enter the Power Factor (PF).

Understand Results

  1. The calculator provides the Full Load Amps (FLA).
  2. It then calculates the Recommended Breaker Amps (FLA x 125%).
  3. Always round up the recommended breaker amps to the next standard breaker size available.

Safety & Standards

  1. Calculations are based on common electrical standards (e.g., NEC).
  2. Always consult local electrical codes and a qualified electrician for final sizing.
  3. Ensure the breaker's interrupting rating (AIC) is sufficient for the fault current.

Breaker Sizing Fundamentals

Full Load Amps (FLA)

FLA is the current a generator produces at its rated power output. It's crucial for determining the conductor and overcurrent protection device (breaker) size.

  • Higher power or lower voltage results in higher FLA.
  • Power factor affects FLA for kW-rated generators.

Breaker Sizing

  • Circuit breakers protect conductors and equipment from overcurrents.
  • For continuous loads (like generators), the breaker must be sized at 125% of the full load current to prevent nuisance tripping and ensure safety.
  • Always select a standard breaker size equal to or immediately above the calculated value.

Key Formulas:

kVA to Amps (Single Phase): Amps = (kVA × 1000) / V

kVA to Amps (Three Phase): Amps = (kVA × 1000) / (V × √3)

kW to Amps (Single Phase): Amps = (kW × 1000) / (V × PF)

kW to Amps (Three Phase): Amps = (kW × 1000) / (V × PF × √3)

Recommended Breaker Amps = FLA × 1.25

Calculation Formulas

Full Load Amps (FLA):

kVA (Single Phase):
FLA = (kVA × 1000) / Voltage

kVA (Three Phase):
FLA = (kVA × 1000) / (Voltage × √3)

kW (Single Phase):
FLA = (kW × 1000) / (Voltage × Power Factor)

kW (Three Phase):
FLA = (kW × 1000) / (Voltage × Power Factor × √3)

Recommended Breaker Size:
Breaker Amps = FLA × 1.25

Example Calculation

Three Phase Generator (kVA):

Generator Power: 50 kVA

Voltage: 480V

Phase: Three Phase

FLA = (50 × 1000) / (480 × √3) = 50000 / (480 × 1.732) ≈ 60.15 A

Recommended Breaker Amps = 60.15 A × 1.25 ≈ 75.19 A

Result: FLA = 60.15 A | Recommended Breaker Amps = 75.19 A

A 80 Amp or 90 Amp standard breaker would typically be selected.

Related Power Calculators

Diesel Generator Sizing Calculator

Calculate the appropriate size for a diesel generator based on your load requirements.

Try Calculator

Commercial Generator Sizing Calculator

Determine the right generator size for commercial applications.

Try Calculator

Generator Fuel Consumption Calculator

Estimate the fuel consumption of your generator over time.

Try Calculator