Breaker Size Calculator
Calculate the proper circuit breaker size for electrical appliances and loads with safety factors
Circuit Configuration
Appliances (Input up to 5 appliances)
Appliance A
Appliance B
Appliance C
Appliance D
Appliance E
Breaker Size Results
Calculation Method: I = W/V
Safety Factor: 125% (1.25) applied to total load current
Standard Sizes: 15A, 20A, 25A, 30A, 35A, 40A, 45A, 50A, 60A, 70A, ...
Load Analysis
Example Calculations
Microwave Circuit Example
Setup: 230V AC single-phase
Microwave: 1000W, Power Factor: 0.72
Load Calculation: I = 1000W ÷ (230V × 0.72) = 6.04A
Required Breaker: 6.04A × 1.25 = 7.55A
Standard Breaker: 15A (closest standard size)
Dishwasher Circuit Example
Setup: 230V AC single-phase
Dishwasher: 1800W, Power Factor: 0.88
Load Calculation: I = 1800W ÷ (230V × 0.88) = 8.89A
Required Breaker: 8.89A × 1.25 = 11.11A
Standard Breaker: 15A (closest standard size)
Standard Breaker Sizes
And more: 175A, 200A, 225A, 250A, 300A, 350A, 400A
Safety Guidelines
Always use 125% safety factor minimum
Match wire ampacity to breaker rating
Consult licensed electrician for installation
Never exceed 80% of breaker capacity
Circuit Types
DC Circuits
I = W ÷ V
Direct current applications
AC Single-phase
I = W ÷ (V × PF)
Residential applications
AC Three-phase
I = W ÷ (V × PF × √3)
Industrial applications
Understanding Circuit Breaker Sizing
What Does a Circuit Breaker Do?
A circuit breaker protects electrical appliances when an overload or fault occurs in the circuit. It automatically cuts power when current exceeds safe levels, preventing equipment damage and fire hazards.
Common Causes of Breaker Trips
- •Overload: Too many devices connected to one circuit
- •Short circuit: Hot wire touches neutral wire
- •Ground fault: Hot wire contacts conductive surface
Sizing Guidelines
125% Safety Factor
Always size breakers for 125% of the calculated load (25% extra capacity) minimum. This prevents nuisance tripping and ensures safe operation.
80% Rule
Continuous loads should not exceed 80% of the breaker's rating. For example, a 15A breaker should handle maximum 12A of continuous load.
Wire Compatibility
Always ensure the wire ampacity matches or exceeds the breaker rating. Undersized wires can overheat even with properly sized breakers.