Every fuse in a van or RV electrical system exists for one reason: to protect the wire from overheating in a fault. Get the sizing logic right and the rest follows.
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The one rule
A fuse protects the wire, not the appliance. Every conductor needs overcurrent protection sized at or below its safe ampacity, placed as close as practical to the power source.
Fuse size = at least 1.25× the continuous load current, but never more than the wire's rated ampacity.
If a wire is rated for 30A and your load draws 20A continuously, the fuse should be roughly 25A — comfortably above the load, but at or below the wire's 30A limit.
Fuse types for a van/RV system
| Fuse type | Typical use | Current range |
|---|---|---|
| Blade (ATC/ATO) | Branch circuits — lights, pumps, fans, USB | 1-30A |
| ANL / MIDI | Inverter, DC-DC charger, larger DC runs | 50-300A |
| Class T | Main battery fuse on LiFePO4 banks | 100-400A |
| Mega fuse | Alternative to ANL for some main-circuit setups | 100-300A |
Why LiFePO4 needs a Class T main fuse
LiFePO4 batteries can deliver extremely high short-circuit current — far more than a lead-acid battery of similar size. A standard blade or ANL fuse may not have a high enough interrupt rating to safely clear that fault current; it can arc internally and fail to open the circuit. A Class T fuse has a high interrupt rating (20,000A+) specifically designed for this.
Fuse the positive conductor only
Always place fuses in the positive (hot) wire, never the negative/ground. Fusing the negative would leave the rest of the system live to the chassis even after the fuse blows — defeating the purpose entirely.
Placement: as close to the source as possible
The main battery fuse should sit within about 7 inches of the battery's positive terminal. Every branch circuit off the bus bars gets its own fuse, sized to that specific circuit's wire and load — not a single fuse covering multiple circuits.
Worked example
A DC-DC charger rated for 50A continuous, wired with 6 AWG cable (rated for ~75A in this application):
Fuse size ≈ 50A × 1.25 = 62.5A, rounded to a standard size — a 60A or 65A ANL/MIDI fuse, which is below the cable's 75A rating. ✓
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