Marine Fuse Sizing
Fuses protect the wire from overload. Size the fuse for the wire, not the load. NEC and SAE require 125% of continuous current. See our boat electrical architecture for the full design guide.
The 125% rule
A 10A continuous load needs a fuse of at least 12.5A; round up to the nearest standard size (15A). The wire must carry that current. Use our fuse sizing calculator for continuous loads.
Placement and protection
Place fuses as close to the power source as practical. Each branch circuit needs overcurrent protection. For motors with high inrush (bilge pumps, windlasses), consider slow-blow (time-delay) fuses.
Workflow
1. Size wire for current and voltage drop. 2. Check wire ampacity. 3. Size fuse at 125% of load, not exceeding wire ampacity. 4. Verify calculate voltage drop and AWG sizing calculator. For battery loads, use battery runtime calculator.