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  1. Home
  2. Units & math
  3. Circuit breaker size calculator
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Circuit breaker size calculator

Pick a standard breaker rating for your circuit and see each coordination rule checked with a pass or fail and the reason.

This tool is in beta

Still being tested. If a result looks wrong, tell us.

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Enter the design current and cable capacity to size the breaker.

The multipliers here are starting points from common practice, such as 250 percent of full-load current for motors and 125 percent for continuous loads. Real coordination work also considers upstream devices, selectivity between breakers, ambient derating already inside Iz, and the local code text, which wins every time it differs from this page. Nothing you type leaves the tab.

Circuit

Rules mode
Load typeSets the default multiplier and the trip curve
More settings▾

The override replaces the load-type multiplier, from 1 to 20. Use it to price in a clause this tool does not encode.

Currents and voltages stay within 1,000,000. The tool checks arithmetic against standard tables; it does not read your local code for you.

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