Breaker & OCPD Sizing Calculator
Selects the next standard overcurrent device size at or above the required amperage per 240.6(A), applies the 240.4(D) small-conductor OCPD ceiling, and sizes a disconnect from motor FLC or RLA.
What it calculates
- Standard OCPD size for a given conductor ampacity, honoring the 240.4(D) ceiling for 14/12/10 AWG conductors
- Disconnect switch size from full-load or running-load amperage
- Dwelling service conductor sizing
- Current ↔ kVA conversion for single- and three-phase systems
Typical inputs
- Conductor ampacity or load current
- Conductor material and size
- Whether the next-size-up allowance (240.4(B)) applies
Frequently asked
What is the 240.4(D) small-conductor rule?
It caps the OCPD at 15A for 14 AWG copper, 20A for 12 AWG, and 30A for 10 AWG, regardless of the conductor's calculated ampacity — a protection against a high-temperature-rated conductor being paired with an oversized breaker.
Autodesk and Revit are registered trademarks of Autodesk, Inc. SYMATEQ is not affiliated with, endorsed by, or sponsored by Autodesk, Inc. SYMATEQ Electrical Calculators is an independent add-in for Autodesk® Revit®. Calculations are engineering aids and do not replace review by a licensed professional engineer or confirmation with the authority having jurisdiction.