Ultimate DC Cable Sizing / System Wiring Calculator for RVs/Caravans

This interactive calculator will help you understand your RV's full power system, including the inverter, battery charger, DC-DC Charger, battery, solar panels, MPPT, and cable sizing with voltage drop. Simply select the voltages and size of your equipment, and the calculator will recommend the optimal cable, fuse, and busbar size, and provide the expected voltage drop.

How to Use the Calculator

All data entry fields are adjustable to match your system's specifications. You can even change the battery voltage to 12, 24, 36, or 48V using the drop-down/select box. Any change you make will automatically update all values. For each distance, enter the one-way cable route length in metres between the two items the cable connects (for example inverter to busbar, or starter battery to DC-DC charger). The calculator adds the matching negative cable, so an inverter whose cables run 3m is entered as 3m.

Output and Results

As you adjust the input values, the calculator automatically recalculates all outputs.

What the Calculator Checks

For each circuit, the calculator works out the current and recommends a fuse rated above it. It then selects the smallest cable in its list that is rated for at least that fuse and keeps the voltage drop within these limits:

Cable sizes considered are 4mm, 5mm and 6mm automotive cable; 8, 6, 4 and 2 B&S; 50, 70 and 95mm²; and two 50, 70 or 95mm² cables in parallel. Panel-to-controller runs use 4mm² or 6mm² PV1-F solar cable, or 8 or 6 B&S marine cable. Voltage drop counts both the positive and the negative cable over the one-way distance you enter. The inverter current is calculated from its rating and the nominal battery voltage, allowing 90% inverter efficiency for the voltage-drop check. The DC-DC charger’s input current allows for its charging voltage (about 14.4V on a 12V bank) and 90% conversion efficiency. The solar controller size is estimated as array watts × 0.9 ÷ battery voltage, which allows about 10% for real-world panel losses and suits an MPPT controller that allows over-paneling, such as Victron. Cable current ratings for 50, 70 and 95mm² use AS/NZS 3008.1.1 values for one spaced pair in free air at 40°C, as listed on our cable product pages; derate cables that are bundled, enclosed or in hot locations. B&S ratings use AS/NZS 3008 values for twin-core 90°C cable in free air at 40°C, so single-core cable has a little extra margin. Two cables in parallel are rated at twice the single-pair value, which assumes equal-length runs spaced apart. The controller-to-battery voltage drop is checked at the fuse rating. Solar cable is sized for at least 1.25 × the array current, and string fuses for parallel strings are about 1.5 × the panel’s short-circuit current; never use a fuse larger than the panel’s maximum series fuse rating. A result of “No listed cable” means no cable in the list meets the voltage-drop and current limits: shorten the run or split the circuit. A fuse of “>800A” needs a specialist design. To convert between mm, mm², B&S and AWG sizes, see our cable size conversion tables. For more on inverter fuses, read how to determine the correct fuse for your inverter. To size a single cable run with a wiring diagram, use our RV Cable Sizing and Wiring Diagram Tool.

Limitations

Please note that the visual representation will only show up to 2 panels in series, 2 panels in parallel, and a maximum of 2 batteries. Any further increase won't display additional panels or batteries, but the calculations will still be accurate.

Request a System Quote

Once you have your results, you can email a screenshot to us at info@solar4rvs.com.au to request a system quote. We're here to help make your RV or caravan's power system as efficient and reliable as possible.

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