How to Wire an Inverter in a Campervan: Step-by-Step Guide

Choosing the right inverter is the first step — wiring it correctly is what makes it safe. An inverter installation that fails usually fails at one of three points: the DC cables are too thin, the fuse is too far from the battery, or the AC output is not properly protected.

This guide takes you through a complete inverter installation from battery to socket. For help choosing the right size inverter first, see our inverter sizing guide and our best inverter roundup.

Before You Start: Understanding the Current Draw

The most important concept in inverter wiring is that a 12V inverter draws far more DC current than the AC watts it delivers. The maths:

DC current = AC watts / (12V × efficiency)

A 2000W inverter at 85% efficiency draws: 2000 / (12 × 0.85) = 196A

That is nearly 200A flowing through your DC cables at full load. This is why inverter cables must be short and heavy — there is no other component in a campervan system that demands this level of care.

Cable Sizing

DC Input Cables (Battery to Inverter)

Size these cables based on the inverter's maximum continuous current draw. Do not use the inverter's rated wattage directly — use the DC amperage:

These assume a cable run of under 1 metre each way. For longer runs, increase by one cable size. See our wire gauge calculator for precise voltage drop calculations.

Cable Length

Keep the DC cables between battery and inverter as short as possible — ideally under 50cm, absolute maximum 150cm. Every extra metre of cable adds resistance, voltage drop, and wasted energy. Mount the inverter close to the battery.

Cable Quality

Use flexible tinned-copper welding cable or purpose-made battery cable. Standard rigid cable is unsuitable — it cannot flex under vibration and will crack at terminations over time. Always use cable with a minimum voltage rating of 600V even though you are working at 12V — the insulation quality is what matters for mechanical durability.

The Main Fuse

The inverter must have its own ANL fuse on the positive DC cable, fitted as close to the battery as possible — within 30cm.

Size the fuse at 125% of the inverter's maximum DC current:

Use an ANL fuse holder, not a blade fuse. Blade fuses are not rated for these currents. Bolt-down ANL fuses make solid, reliable connections that can handle the sustained high current an inverter demands.

Connecting to the Battery

Terminals

Use compression lugs (also called cable lugs or ring terminals) correctly sized for your cable gauge and the battery terminal bolt. Hydraulic crimping is preferred for cables above 16mm² — hand crimpers do not provide sufficient force for reliable large-lug terminations. Some builders solder large lugs, but proper crimping is mechanically stronger and preferred.

Positive and Negative

Connect positive (red) to battery positive, negative (black) to battery negative. Do not connect to a bus bar unless the bus bar is rated for the full inverter current — most standard bus bars are not. The inverter should have its own dedicated direct connection to the battery.

Tighten Properly

Battery terminal bolts and ANL fuse holder connections must be torqued to specification. Loose connections arc under load, causing heat, voltage drop, and eventually failure. Check these connections annually.

Inverter Placement

Location Requirements

• Within 1.5 metres of the battery (cable length constraint)
• Good ventilation — inverters generate significant heat at high loads
• Not in a sealed compartment without airflow
• Not in the cab or near passengers (electromagnetic interference from the switching circuitry)
• Accessible for the remote switch wiring if you are using one

Mounting

Mount the inverter on its side or flat — check your manufacturer's guidance. Most need airflow along the heat sink fins, which are typically on the sides. Leave 100mm clearance on all sides. Bolt it firmly — vibration loosens DC connections at the inverter terminals.

Remote On/Off Switch

Most inverters have a remote on/off connection — two small terminals or a connector that, when bridged, turns the inverter on. This allows you to mount a simple switch in a convenient location (dashboard, kitchen area) and avoid reaching to the inverter itself each time.

Wiring the Remote Switch

Connect a standard 2-core wire (0.75mm² is sufficient — this carries only a signal voltage) from the remote terminals on the inverter to a rocker or toggle switch mounted where you want it. The polarity is usually not critical — check your inverter manual.

Some inverters also accept a 12V signal on the remote terminal, allowing the inverter to be switched on automatically when you press a button elsewhere in the van's 12V system.

Why Use Remote Switch

• Convenience — switch the inverter on/off without reaching behind panels
• Safety — allows quick shutdown from the living area
• Battery saving — inverters draw 10-25W on standby even with no AC load. See our inverter standby drain guide for the full picture.

Connecting the AC Output

The inverter's 230V AC output needs to be safely distributed to your sockets.

Option 1: Direct Socket Connection

For a simple installation, connect the inverter's AC output directly to one or two 230V sockets using 2.5mm² three-core flex (brown live, blue neutral, green/yellow earth). The inverter's built-in protection covers the AC output.

Option 2: Through a Consumer Unit

For a more complete installation — particularly if you also have shore power hook-up — run the inverter's AC output into a transfer switch or changeover switch, which selects between shore power and inverter. Then feed through a consumer unit with RCD and MCBs protecting individual circuits. This gives you proper fault protection on every circuit regardless of whether you are on shore power or inverter. See our consumer unit wiring guide.

AC Cable Sizing

The inverter's AC output operates at 230V, so the currents are much lower than the DC side. For a 2000W inverter at 230V: 2000/230 = 8.7A. Standard 2.5mm² flex is adequate for all but the largest inverters.

AC Fusing

The AC output needs overcurrent protection. If you are connecting directly to sockets without a consumer unit, fit an inline fuse or MCB rated at 13A (for standard 13A sockets) in the live conductor.

Earthing the Inverter

The inverter chassis should be earthed to the van's 12V chassis earth (battery negative). Most inverters have a dedicated earth terminal — connect this with a short length of green/yellow 6mm² cable to your negative bus bar or directly to the chassis earth point. This is covered in detail in our earth bonding guide.

The 230V AC earth from the inverter's output must also be connected — either to the consumer unit earth bar or directly to the chassis earth, maintaining the single-point bonding principle.

Full Wiring Summary

Battery (+) ──── ANL Fuse (within 30cm) ──── Inverter DC+
Battery (-) ──── Inverter DC-
Inverter Earth Terminal ──── Chassis Earth

Inverter AC Live ──── Consumer Unit / MCB ──── Sockets
Inverter AC Neutral ──── Consumer Unit / Neutral Bar ──── Sockets
Inverter AC Earth ──── Consumer Unit / Earth Bar ──── Chassis Bond

Remote Switch ──── (signal wire) ──── Inverter Remote Terminal

Common Installation Mistakes

Using Cable That Is Too Thin

The most common and most dangerous mistake. If your 2000W inverter cable gets warm during use, it is undersized. Warm cable means wasted energy and a fire risk. Replace with the correct gauge before using the inverter at load.

Fuse Too Far From Battery

An ANL fuse holder mounted near the inverter — rather than at the battery — leaves 1-2 metres of unprotected cable between battery and fuse. This cable can carry hundreds of amps if it shorts. The fuse must be at the battery end.

No Remote Switch

Running the inverter with no way to quickly shut it down means it draws standby power around the clock and you cannot isolate it quickly in an emergency. Fit the remote switch — it takes 20 minutes and costs £5.

No Earth Connection

An inverter with no chassis earth cannot safely trip an RCD if a fault develops on the AC output. Always earth the inverter chassis.

FAQ

Can I connect the inverter to my fuse box instead of directly to the battery?

Only if your fuse box and bus bar are rated for the full inverter current, and only if the connection from the battery to the fuse box is also rated accordingly. In most builds it is simpler and safer to connect the inverter directly to the battery with its own fuse.

Does the inverter need ventilation?

Yes. An inverter running at 80% of its rated load generates significant heat. Mount it in a ventilated space and ensure the heat sink fins have airflow. Operating an inverter in a sealed compartment shortens its life and is a potential fire risk.

Can I run the inverter and shore power at the same time?

Not without a transfer switch or changeover switch that physically prevents the two supplies from connecting to the same sockets simultaneously. Connecting inverter and shore power together without isolation will damage both the inverter and potentially the shore power supply.

My inverter keeps tripping on overload — what is wrong?

Either the load is exceeding the inverter's rated capacity, or the DC cable voltage drop is causing the inverter's low-voltage shutdown to trigger. Check: (1) what you are plugging in and its actual wattage, (2) whether the DC cable is the correct gauge, (3) the battery state of charge when tripping occurs.