I'm in the process of outfitting my camper van with a solar array and have purchased the components from Renogy, but I'm stuck on the installation details. My system operates at 12V with 600W of solar power. The MPPT controller manual specifies using 6 AWG wire between the controller and the leisure battery, and between the controller and the vehicle's starter battery. It also advises a 75-100A ANL fuse for each positive lead. However, based on my calculations, 6 AWG wire can handle only 60-65A. This leads me to wonder if the wire would fail before the fuse in case of an issue. I've encountered a similar situation with the inverter charger, which requires a 4/0 wire and a hefty 400A ANL fuse. Given that 4/0 wire can handle 260A, I question whether it too would be at risk of failing before the fuse would blow. I reached out to Renogy support for clarification, but they just reiterated the manual without going deeper into the explanation, leaving me a bit uneasy. What am I missing regarding the relationship between wire size and fuse ratings?
2 Answers
The main thing to understand is that the purpose of the fuse is to protect your system from the battery side rather than the other way around. If you're in a situation where more amps can be delivered under normal conditions, you should really look into thicker wire. Generally, the fuses are rated about 25% higher than the continuous rating of the wire, so they are designed to handle temporary surges. You definitely don’t want a fuse blowing under normal operation; it should only blow if something goes wrong.
You're right to consider voltage and wire type, as they affect how much current a wire can handle. Different wires have different ampacity ratings depending on the voltage and conditions, so it’s possible for wires to carry more current at lower voltages. Check out resources like [Wiringo's](https://www.wiringo.com/6-awg-wire.html) voltage charts for more insights. However, your concern is valid: if you're calculating based on a 12V system and comparing it to 120V, the lower voltage allows for potentially much higher currents, making the fuse an important weak link in your setup.