Circuit Breaker Sizing
Estimate recommended breaker size with safety factor based on load voltage and current.
Understanding Circuit Breakers
A circuit breaker is a safety device designed to protect your wires from overheating. It "trips" (shuts off power) if the current flowing through it exceeds its rating.
The 80% Rule
For continuous loads (devices that run for 3 hours or more, like heaters or EV chargers), you should only load a breaker to 80% of its capacity.
20 Amp Breaker: Max continuous load = 16 Amps.
15 Amp Breaker: Max continuous load = 12 Amps.
Types of Protection
Standard Breaker
Protects against overloads (too many devices) and short circuits (hot wire touching neutral).
- Use: General lighting, older appliances
GFCI & AFCI
Advanced protection required by modern code.
- GFCI: Prevents shock (wet areas like kitchens/baths).
- AFCI: Prevents fires (detects arcs/sparks in bedrooms).
Frequently Asked Questions
How to use the Circuit Breaker Sizing
Follow these steps to get accurate results with the circuit breaker sizing.
- 1
Enter your values
Fill in the required input fields above. Units can be changed where available.
- 2
Click Calculate
Press the calculate button to compute results instantly in your browser.
- 3
Review your results
View the computed outputs and use related calculators for deeper analysis.
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