What Cable Size for 12V Campervan Wiring?
Choosing the correct cable size is one of the most important parts of any 12V campervan electrical system. If the cable is too small, voltage drop increases, equipment may not work properly and the cable can overheat. This guide explains how to choose the right cable size for common campervan circuits and when to move up to a larger cable.
Quick answer
There is no single cable size for all 12V campervan wiring. The correct size depends on current draw, cable length and acceptable voltage drop.
Small lighting circuits may use a much smaller cable than a fridge feed, diesel heater feed, inverter cable or battery charging circuit. In 12V systems, cable length matters a lot because voltage drop becomes noticeable very quickly.
For the most accurate answer, use the: Cable Size Calculator, then verify the result with the Voltage Drop Calculator and choose protection using the Fuse Size Calculator.
What affects cable size in a 12V campervan?
In a campervan, cable size is usually driven by three main factors:
- Current draw – higher current needs thicker cable.
- Cable run length – longer runs increase resistance and voltage drop.
- Voltage drop target – sensitive circuits often need a lower drop.
Because campervan systems usually run at 12V, even a small voltage loss can make a noticeable difference. A drop that might be acceptable on a higher-voltage system can be too much for a 12V fridge, fan, pump or charging circuit.
Typical voltage drop targets
Different campervan circuits can tolerate different voltage drop limits. A practical starting point is:
| Circuit type | Typical voltage drop target | Notes |
|---|---|---|
| LED lights, electronics, chargers | 3% | Best where stable voltage matters. |
| General accessory circuits | 5% | Often acceptable for pumps, fans and simple loads. |
| Fridge supply | 3% | Lower drop is usually better for reliable performance. |
| Battery charging circuits | 2%–3% | Important for DC-DC chargers and efficient charging. |
| Inverter supply cables | As low as practical | High current means cable size often increases quickly. |
Common campervan circuits and cable sizing examples
The examples below are general guidance only. Always calculate based on your actual current draw and cable length.
| Example circuit | Typical load | What matters most |
|---|---|---|
| LED lighting | Low current | Usually easy to size, but long runs still matter. |
| 12V fridge | Moderate current | Keep voltage drop low for reliable operation. |
| Diesel heater | Moderate current, startup spikes | Good cable sizing helps avoid startup issues. |
| Water pump | Short bursts | Often straightforward, but fuse correctly. |
| DC-DC charger | Higher current | Low voltage drop becomes much more important. |
| Inverter cable | Very high current | Usually requires much larger cable than small accessory circuits. |
This is why a campervan should not be wired with “one cable size for everything”. Different circuits need different cable sizes.
How to choose the right cable size
1. Work out the load current
Start with the current draw of the appliance or circuit. If you only know the power in watts, you can estimate current from power and voltage.
2. Measure the one-way cable run
Measure the actual route the cable will take, not the straight-line distance. Longer routes increase voltage drop.
3. Decide on your voltage drop target
Sensitive circuits usually deserve a lower voltage drop target than basic accessory wiring.
4. Use a calculator
Use the Cable Size Calculator to estimate the required cable cross-section.
5. Check fuse size
Once you know the cable and load, use the Fuse Size Calculator to estimate a suitable fuse size.
Why voltage drop matters so much in campervans
In a 12V campervan, losing even a small amount of voltage can have a noticeable effect. Fridges may perform less efficiently, chargers may not work as expected, and some electronics may see reduced voltage under load.
That is why longer cable runs to the rear of the van, roof circuits, battery charging cables and inverter cables often need more attention. A cable that looks big enough based only on current may still be too small once voltage drop is taken into account.
Useful tools for sizing campervan wiring
The fastest way to get the right answer is to use the calculators together.
Recommended MKGT cable ranges
After sizing your circuit, move into the most relevant cable type for the application.
Frequently asked questions
Can I use the same cable size for all campervan circuits?
No. Lighting, pumps, fridges, charging circuits and inverter feeds all have different requirements.
What cable size should I use for a campervan fridge?
That depends on the fridge current draw and cable run length. Fridge circuits often benefit from a lower voltage drop target than general accessory circuits.
Do longer cable runs always need thicker cable?
In most cases, yes. Longer runs increase resistance and therefore voltage drop.
Should I size cable only by fuse size?
No. Fuse size is only one part of the picture. You also need to consider current draw, cable length and voltage drop.
Start with the calculator
The easiest way to size a campervan cable properly is to calculate it first, then check voltage drop and fuse protection.