Dual 3kW Inverters in a Tow-Behind Camper: The 24V Wiring Blueprint

I helped a buddy wire up a 30-foot tow-behind last year with this exact architecture, and the decision to go 24V instead of 12V saved us probably $800 in copper alone. Let me walk through the key decisions.

Parallel vs split-phase is the first fork in the road. In North America, if you want to run a 240V appliance (like certain dryers or water heaters), you need split-phase — each inverter produces one 120V leg, 180 degrees apart, giving you 240V between the two hot legs. But if all your loads are 120V, parallel mode doubles your capacity to 6,000VA on a single 120V circuit. Most tow-behind campers use parallel mode since RV appliances are all 120V.

The Victron MultiPlus is ideal here because it has a built-in transfer switch and charger. When you plug into the 50A shore power pedestal, it automatically switches from inverting to pass-through and starts charging the batteries at up to 70A per unit (140A total at 24V). That's over 3,300W of charging power, which can refill a 400Ah bank from 20% to full in about 6-7 hours.

Cable sizing is where 24V really shines. The run from battery bank to inverters needs to handle 260A worst case. At 24V with a 1-meter cable run and 1% voltage drop target: mm² = (2 x 1 x 260) / (57 x 0.24) = 38mm². So 50mm² cable gives you comfortable margin. At 12V, same calculation gives you 76mm² — you'd need 95mm² cable, which costs roughly double and is nearly impossible to bend in tight spaces.

The 50A inlet needs proper wiring too. A 50A RV plug (NEMA 14-50) actually carries two 50A hot legs at 120V each in a split-phase setup. If you're running parallel single-phase, you'll wire both hot legs together through a proper junction, or better yet, use a 30A inlet (TT-30) if you don't need the full 50A shore capacity.

Battery fusing: each inverter gets its own fused disconnect. At 130A max per unit, use a 150A or 175A Class T fuse on each. The main battery bank should have a 300A or 400A master fuse. Don't skip the fusing — at 260A, an unfused short circuit will melt copper and start fires in seconds.