MKGT Campervan 12V Wiring Guide

Campervan 12V wiring at a glance

Every campervan electrical system should be designed for worst-case conditions: all circuits running at the same time, warm ambient temperature and cable routed through panels, insulation or conduit.

01 Introduction — why wiring matters

Incorrect 12V wiring can cause overheating, faults and, in the worst case, fire. The most common problems are undersized cable, missing fuses, poor connections and wrong cable types.

This guide explains the basic structure of a safe 12V leisure system, from the battery to the device. The goal is simple: use the correct cable, protect it with the correct fuse and install it in a way that survives vibration and daily use.

02 Cable selection — stranded vs solid

Never use household twin and earth cable in a vehicle. Household cable usually has a solid copper core, which can work-harden and fail under vibration.

Campervans move, vibrate and flex. For this reason, you should use stranded flexible automotive cable. Stranded cable contains many small copper strands, making it much better suited to vehicle installations.

03 Cable sizing — British Standard cable table

Cable sizing is not only about amps. It is about amps and cable length. Longer cable runs have more resistance, which increases voltage drop and heat.

Current carrying capacity reference

Practical cable sizes for common campervan devices

Use the free MKGT calculator: Cable Size Calculator

04 Fuse sizing — the formula

The fuse protects the cable, not the device. This is one of the most important rules in 12V campervan wiring.

Standard blade fuse sizes commonly include 3A, 5A, 7.5A, 10A, 15A, 20A, 25A, 30A, 40A and 50A. Higher-current circuits usually use ANL fuses.

Use the free MKGT calculator: Fuse Size Calculator

05 Wiring diagram — complete 12V system

A complete campervan leisure system normally starts at the leisure battery, passes through a main fuse, then feeds a distribution board. Each device then has its own correctly fused circuit.

Leisure battery → main ANL fuse → main feed cable → fuse board → individual circuits → negative busbar → battery negative

System walkthrough

• Battery: 12V AGM or lithium leisure battery, kept separate from the starter battery.
• Main ANL fuse: main protection for the feed cable, installed close to battery positive.
• Main feed cable: heavy cable from fuse to distribution board.
• Distribution board: individual fused circuits for each device.
• Negative busbar: all device negatives return to battery negative.
• Individual circuits: each device has its own fuse and correctly sized cable.

06 Cable installation — conduit, grommets and clips

Use PVC conduit wherever possible

Van bodywork has sharp metal edges that can damage cable insulation over time. Conduit protects cables from chafing and vibration wear.

Use grommets at every panel penetration

Wherever cable passes through a metal panel, fit a rubber grommet. This prevents the metal edge from cutting into the insulation.

Clip cables every 300mm

Loose cables move and rub against surfaces. Clip cables regularly to prevent movement and chafing.

Label every circuit

Label circuits at the fuse board and at the device end. This makes future fault finding much faster.

Use proper crimped or soldered connections

Avoid household-style connector blocks. Use automotive crimp connectors with adhesive heat shrink, or soldered joints with heat shrink where appropriate.

07 Most common campervan wiring mistakes

08 Free MKGT calculators

Use these calculators to check cable size, fuse size, voltage drop, runtime and solar requirements for campervan electrical systems.

09 Shop campervan wiring cable

MKGT supplies automotive cable cut to length, including battery cable, 2 core flat cable, 2 core round cable, multicore cable and solar cable.

Electrical installation safety notice

This guide and the associated calculators are provided for general educational purposes only. They show typical wiring layouts and estimation methods commonly used in UK 12V campervan electrical systems.

Every campervan installation is different. Cable sizing, fuse selection, battery chemistry, inverter rating and ventilation requirements should always be checked against manufacturer specifications and the requirements of your specific vehicle.

Where high-current battery systems, DC-DC chargers, inverters or 230V mains hook-up equipment are involved, installation should be completed or inspected by a suitably qualified installer.