Circuit Breaker Sizing Calculator Guide
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).