How to choose fuses for your camper van: complete guide

A fuse is a deliberate weak point in your electrical circuit. When too much current flows through a cable, whether from a short circuit, a faulty device or an overloaded circuit, the fuse blows before the cable overheats. Without a fuse, the cable itself becomes the weakest point. Overloaded copper wire gets hot enough to melt its insulation, and once bare copper touches something flammable, you have a fire. In a camper van this risk is amplified. Your cables run through walls, behind panels and under floors, places you cannot see or reach. A smouldering cable behind your wall cladding can go unnoticed until it is too late. The golden rule of fuse selection: the fuse protects the cable, not the device. You size the fuse based on the maximum safe current the cable can carry, not on what the connected device draws. If you use a 2.5 mm² cable rated for 21A, the fuse should be 20A or less, regardless of whether the device only draws 5A. Every positive cable leaving your battery or fuse box must be fused. No exceptions. This includes cables to lights, the fridge, USB outlets, the water pump and especially the high-current cable to your inverter.

There are several fuse types commonly used in camper van installations, each suited for different current ranges. Blade fuses (also called ATO or ATC fuses) are the most common for low to medium current circuits. They come in mini, standard and maxi sizes, covering 1A to 80A. They are cheap, easy to replace and fit in standard fuse holders and fuse boxes. Use them for lighting, USB, fridge, water pump and other circuits up to about 40A. ANL fuses (also called wafer fuses or strip fuses) handle high currents from 40A up to 500A or more. They are used for the main battery cable, inverter cable and battery-to-battery (B2B) charger connections. They require a dedicated ANL fuse holder bolted to the cable lugs. Mega fuses are similar to ANL fuses and cover 100-500A. They are often used as the main battery fuse. Circuit breakers are resettable alternatives to fuses. Instead of replacing a blown fuse, you simply flip the breaker back. They are convenient for circuits that occasionally trip, but they are more expensive and bulkier. Some builders use a main circuit breaker as a master disconnect. NH fuses (Niederspannungs-Hochleistung, low-voltage high-performance) are industrial-grade fuses used in some high-end camper van builds for the main battery protection. They are very reliable but require specific fuse holders.

Sizing a fuse correctly requires knowing two things: the cable's current-carrying capacity and the expected load current. Step 1: Check your cable rating. Every cable cross-section has a maximum continuous current rating. For example, 1.5 mm² handles about 16A, 2.5 mm² handles 21A, 4 mm² handles 27A and 6 mm² handles 35A. These values assume open-air installation and may be lower in conduit or bundles. Step 2: Choose a fuse at or below the cable rating. The fuse must blow before the cable reaches its limit. For a 2.5 mm² cable rated at 21A, a 20A fuse is correct. A 25A fuse would be too high and would not protect the cable. Step 3: Ensure the fuse is above the normal operating current. If your fridge draws 8A, a 10A or 15A fuse works fine on a 2.5 mm² cable. But a 5A fuse would blow during normal operation. The formula is simple: device current < fuse rating <= cable rating. For example: fridge (8A) < 15A fuse <= 21A cable rating. That works. For motor-driven devices like compressor fridges or water pumps, account for startup surge. A pump drawing 5A steady may spike to 15A on startup. If a 10A fuse blows on startup, go to 15A, but make sure your cable supports it. Always err on the side of a slightly larger cable rather than a larger fuse. Oversizing the cable costs a few euros more but significantly improves safety.

A well-organized fuse box is the heart of your 12V distribution system. It is where all your circuits come together, each individually fused and easy to troubleshoot. Choose a fuse box with enough slots for all your circuits plus a few spares for future expansion. A 12-way blade fuse box is a good starting point for most camper vans. Mount it in an accessible location, not behind a panel you need to unscrew. Many builders install it under the bed or in a dedicated electrical cabinet. Feed the fuse box from your battery through a main fuse (typically an ANL or Mega fuse). This main fuse protects the cable between battery and fuse box. Size it for the cable, not the total of all circuits. Label every circuit clearly. Use a label maker or write on tape which fuse goes to which circuit: fridge, lights kitchen, lights bedroom, USB, water pump and so on. This saves hours of troubleshooting later. Connect the negative (ground) cables to a common bus bar near the fuse box. Use a separate bus bar for negative connections rather than running all grounds back to the battery individually. This keeps your wiring tidy and makes fault-finding much easier. Consider a combined fuse and relay box if you want switched circuits. Some fuse boxes come with integrated relays that let you control circuits from a switch panel, a clean solution for a professional-looking installation.