How To Size Wires In A Campervan Electrical System

For typical camper van electrical systems, determining which size wire to use is pretty straight forward. You’ll only need two pieces of information.

• What is the total circuit length?
• How much current will flow through the circuit?

In this post we aim to take the confusion out of calculating wire sizes so you can hit the road sooner!

Before calculating, check the manufacturers guidelines

More often than not, component manufacturers list the required wire diameter and maximum wire length in the instruction manual. If there are no guidelines to follow from the manufacturer, you can use the following steps.

How to calculate 12 Volt wire sizes yourself

First determine the maximum amperage that will flow through your circuit. This is the total amperage of all devices that will be connected in this circuit.

Next measure the length of cable needed to complete the circuit. The total circuit length includes both the positive and negative cables in the circuit.

When you have these two numbers you can use the following charts to determine which size wire you need. If you’re in the U.S. you’ll likely need the imperial chart, and if you’re in Europe the metric chart.

These charts are designed using typical automotive standards. Meaning at high amperage draw, there will be a maximum voltage drop of 5%. This is acceptable voltage drop for non critical items like lights, fans, phone chargers etc…

However for more critical components like computers and medical equipment, it’s a good idea to use a wire that’s one size larger than what’s recommended by the chart. This will reduce the circuit resistance, which in turn reduces voltage drop.

If you’re having trouble finding the right wire size for your system, you can use this wire calculator here.

Calculating wire size for large 12 Volt components

Large components like power inverters require large cables because of their high current draw. These cables should be thick and short as possible to keep circuit resistance low and voltage drop low (max 1%).

If using a wire size calculator, design your system to have a max voltage drop of 1%.

The following chart can give you an idea of the required cable and fuse sizes for 12 and 24 Volt power inverters. Always check with the manufacturer’s recommendations before using this chart, your components may require a different cable and fuse combination.

Which wires are compatible with 12 Volt electrical systems?

As a general rule, look for pure copper or copper-tinned wiring. Marine-grade (UL-1426) wiring and welding cables are great options for your system.

Do not use speaker wire or wires that contain aluminum. These wires have different amperage carrying capacities, and if not calculated for, there is an increased risk of fire.

Remember to always purchase quality components from trusted manufacturers. Inferior components lead to increased risk of fire.