Breaker Size Calculator
Determine the correct circuit breaker size for your electrical loads.
Breaker Size Calculator
Compliant with NEC Standards
Results:
Calculated Load Current (A): 0.00
Required Breaker Current (A): 0.00
Recommended Breaker Size (A): 0
How to Use the Calculator
Calculate from Amps
- Select "Amps (Current)" as the calculation method.
- Enter the Load Current in Amperes.
- Select the Load Type (e.g., Motors, Welders).
- Click "Calculate" to get the recommended breaker size.
Calculate from Power (kW)
- Select "Power (kW)" as the calculation method.
- Enter the Power in Kilowatts (kW).
- Select System Type (AC/DC), Voltage, and Phase (for AC).
- Select the Load Type.
- Click "Calculate" to first derive current, then breaker size.
Understanding Safety Factors
- Resistive/Lighting: 25% safety factor.
- AC/Heat Pump: 75% safety factor.
- Welders: 100% safety factor.
- Motors: 25% safety factor.
Circuit Breaker Fundamentals
Purpose of Breakers
Circuit breakers protect electrical circuits from damage caused by overcurrent, which can result from an overload or short circuit. They automatically interrupt the current flow when a fault is detected.
Sizing Principles
- Breakers are sized to protect conductors and equipment.
- Safety factors are applied based on load type to ensure adequate protection and prevent nuisance tripping.
- Standard breaker sizes are used to select the next available rating [^Standard_Breaker_Sizes].
Key Principle:
Required Breaker Current = Load Current × (1 + Safety Factor)
Safety Factor varies by load type (e.g., 0.25 for resistive, 0.75 for AC).
Calculation Logic
Current from Power (kW) Formulas:
DC: I = (kW × 1000) / V
AC Single Phase: I = (kW × 1000) / (V × PF)
AC Three Phase: I = (kW × 1000) / (√3 × V × PF)
Breaker Sizing Formulas:
Required Current = Calculated Load Current × (1 + Safety Factor)
Safety Factors:
- Resistive/Lighting: 0.25
- AC/Heat Pump: 0.75
- Welders: 1.00
- Motors: 0.25
Recommended Breaker Size = Next Standard Size ≥ Required Current
Example Calculation (Power to Breaker)
Consider a 10 kW AC Three Phase Motor Load at 400V, PF 0.8:
Power (kW): 10 kW
System Type: AC, Three Phase
Voltage: 400V, PF: 0.8
Load Type: Motors (25% safety factor)
Calculated Current (I) = (10000) / (√3 × 400V × 0.8) ≈ 18.04A
Required Breaker Current = 18.04A × (1 + 0.25) = 18.04A × 1.25 ≈ 22.55A
Next Standard Breaker Size ≥ 22.55A is 25A.
Recommended Breaker Size: 25A
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