12V Fuse Calculator
Safety first: Disconnect shore power and turn off other charging sources before opening panels or changing RV wiring. A fuse protects the wire, not the device alone. Never replace a fuse with a higher amp rating just to “stop blowing” without finding and fixing the cause. This calculator is educational guidance from Volt Resources—not a substitute for equipment manuals or local electrical code.
Continuous vs intermittent: Size from the continuous load (or continuous charger/converter rating). For continuous loads, a common NEC-style planning factor is 125% (load × 1.25), then round up to the next common fuse size. Intermittent loads may allow different practice—always follow the manufacturer when they specify a fuse.
Calculate DC fuse rating
Enter the continuous current. Optionally add known wire AWG and conductor material to check that the fuse stays at or below approximate wire ampacity (fuse protects the wire).
How to use this fuse calculator
Enter the continuous current of the load or the continuous rating of a charger/converter. The calculator multiplies by 1.25 and rounds up to a common DC fuse size. Optionally enter the wire AWG and copper vs CCA so you can confirm the fuse does not exceed approximate wire ampacity. Fuse type and system voltage only change the context notes—they do not change the 125% math.
Fuse protects the wire
Overcurrent protection is there so the conductor does not overheat under fault or overload. A fuse that is larger than the wire can safely carry leaves the wire unprotected. If a fuse keeps blowing, find the cause—do not fit a higher amp fuse as a workaround. Main battery fuses belong as close to battery positive as practical. For inverters, follow the manufacturer’s continuous and surge fuse guidance; do not undersize for surge or oversize beyond the wire.
Method note
Recommended fuse = continuous amps × 1.25, then the next common stock size: 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 100, 125, 150, 175, 200, 250, 300, 350, 400 A. Wire ampacity values are approximate chassis/RV DC planning figures for copper (~30 °C, short chassis-style runs)—not NEC building-wire tables. CCA is estimated at about 70% of the copper figure for the same AWG. Always confirm with the cable and fuse manufacturers and applicable standards. Volt Resources provides educational guidance only.
For this 30A circuit, I recommend 10 AWG tinned copper wire. See the wire on Amazon.ca