Fuse Sizing Calculator
Continuous-current screening against a declared rating list. Final protection, coordination and inrush acceptance require exact device and installation evidence.
Recommended fuse
15 A
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These calculators are engineering design aids intended for estimation and educational purposes. They do not replace professional engineering judgment or compliance with applicable standards (ABYC, NEC, IEC, SAE, or local regulations). Always verify final designs against relevant codes and manufacturer specifications.
Purpose
This calculator estimates appropriate overcurrent protection size based on continuous current. Size the wire first with the AWG sizing calculator, then size the fuse for the wire ampacity and load.
The 125% rule
Many electrical standards recommend sizing overcurrent protection at up to 125% of continuous load current, provided the conductor ampacity supports that rating and the protection device does not exceed wire limits. Example: 10A continuous load → 12.5A minimum → next standard size (e.g. 15A).
Fast-blow vs time-delay
Fast-blow fuses: suitable for resistive loads (lighting, heaters). Time-delay fuses: better for motors and inrush loads. Motors may briefly draw 2–6× running current during startup.
Important limitations
Fuse sizing must never exceed conductor ampacity. This tool does not replace applicable code compliance or manufacturer specifications. Verify voltage drop stays within limits.
FAQ
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