I’ve wired four campervans from bare metal to fully functional electrical systems. The first one took me six weeks of weekend work and involved three complete rewires after I realised I’d cocked up the cable sizing. The fourth one took me eight days and passed inspection first time.

The difference wasn’t better tools or more expensive components. It was understanding the actual system architecture before I crimped a single cable.

This is the guide I wish existed when I stood in my 2017 VW Transporter surrounded by a pile of cables, batteries, and components, wondering where the hell to start. It’s going to be long – really long, because there’s no shortcut to understanding campervan electrics. But by the end, you’ll know exactly how every component connects, why it connects that way, and how to avoid the mistakes that cost me hundreds of pounds across those first two builds.

This guide will also help you with campervan wiring to ensure a seamless electrical system in your vehicle.

The Big Picture: How a Campervan Electrical System Actually Works

Before we touch a wire, you need to understand what you’re building. A campervan has three separate electrical systems that all work together:

The starter system – Your van’s factory 12V system that starts the engine and runs the headlights, indicators, and dashboard. You’re not rewiring this. Leave it alone.

The leisure system – The 12V system you’re building that powers lights, water pump, fridge, USB sockets, and anything else you want to run. This is powered by a separate leisure battery that’s kept charged by solar panels, the alternator, or shore power.

The 230V mains system – An optional system that lets you plug into campsite hook-up (shore power) and run 230V appliances like a toaster or laptop charger through standard UK plug sockets. This requires an inverter to convert 12V DC from your leisure battery into 230V AC.

These three systems are connected at specific points (we’ll get to those), but they’re fundamentally separate. Understanding this separation is critical. Your leisure battery doesn’t start your engine. Your starter battery doesn’t power your fridge. They’re independent systems with controlled connection points.

Here’s the flow of electricity through a typical system:

Charge sources (solar panels, alternator, shore power) → Charge controllers/chargers → Leisure battery → Fuses/circuit protection → Loads (lights, fridge, pump, etc.)

That’s it. Everything else is just detail.

Component Breakdown: What Each Part Actually Does

Let me walk through every major component you’ll need, what it does, and why you can’t skip it. I’m using components from my four builds as examples, with real part numbers and prices where relevant.

Leisure Battery

This is your power storage. Everything you run on 12V draws from this battery. When it’s depleted, you’ve got no power until it recharges.

The big decision: lithium or AGM?

I ran AGM batteries (absorbed glass mat, a type of sealed lead-acid) for my first three builds. First build had a 110Ah AGM that cost £175 and lasted three years. Second build stepped up to a 230Ah AGM – massive thing, weighed 61kg and cost £340 and gave me four years of service. Third build used the same 230Ah AGM.

Current build i switched to lithium. Specifically, a 200Ah LiFePO4 battery that weighs 23kg and cost £649.

Here’s what I learned across those four builds:

AGM batteries work perfectly fine. You can absolutely wire a campervan with AGM and have a reliable system. The 230Ah unit in my second build powered my fridge, lights, water pump, USB charging, and diesel heater for extended weekends without issue. Three days off-grid in summer was achievable. Winter was tighter because the diesel heater drew more current.

The limitation: you shouldn’t discharge AGM below 50% regularly or you’ll shorten its lifespan dramatically. That 230Ah AGM gave me about 115Ah of usable capacity. When the battery monitor showed 50%, I needed to recharge or risk damaging the battery.

Lithium batteries give you more usable capacity from the same Ah rating. My 200Ah lithium can safely discharge to 10% (180Ah usable) without damage. That’s 65% more usable energy than my old 230Ah AGM, despite being nominally smaller.

Lithium also charges faster. The AGM would accept maybe 25A charging current maximum. The lithium takes 50-60A happily, meaning it recharges in half the time when I’m driving or getting good solar.

But, and this matters – lithium costs 2-3 times more upfront. That £649 battery vs £340 for AGM. Over 2,000+ charge cycles, lithium works out cheaper per usable amp-hour. But if you’re doing a budget build and don’t have £650 to spend on a battery, AGM will serve you well for 3-5 years.

Battery mounting is critical. Batteries are heavy. My 23kg lithium becomes a projectile in an accident if it’s not properly secured. The 61kg AGM from the second build could literally kill someone if it broke free and hit them at motorway speeds.

I mount batteries in a plastic battery box (about £35 from motor factors) that’s bolted to the van floor with M8 coach bolts through the chassis. The battery itself sits in the box and is secured with heavy-duty ratchet straps rated for 800kg. This might seem overkill. It’s not. In a 40mph crash, that 23kg battery experiences forces equivalent to 460kg trying to keep moving forward.

Never mount batteries on their side. Never mount them where they could shift. Never mount them directly against heating systems or external van walls where temperature extremes can reduce performance.

Solar Panels

Solar panels convert sunlight into electricity to charge your leisure battery. I didn’t have solar on my first build (couldn’t afford it on a £3,000 total budget). Second build i got a single 100W panel. Third build i had 175W. My current build has two 175W panels (350W total).

Here’s what actually happens with solar in the UK:

That 100W panel never actually produced 100W. On a perfect June day, parked in full sun at midday, I might see 85W. On a cloudy October day, maybe 15W. On a rainy day parked under trees, bugger all.

But averaged over time, that single 100W panel gave me about 30-40Ah of charge per day in summer, 10-15Ah in winter. Enough to offset my LED lighting and water pump usage, but not enough to run a fridge or recover from running the diesel heater overnight.

The two 175W panels on my current build average 60-80Ah per day in summer, 20-30Ah in winter. This is enough to run my compressor fridge continuously and still have surplus going into the battery. Game-changer for off-grid capability.

Panel types matter less than you’d think. I’ve used monocrystalline (slightly more efficient, black appearance) and polycrystalline (slightly less efficient, blue appearance with visible crystal pattern). In real-world UK conditions, the difference is maybe 5%. What matters more is total wattage and how you mount them.

I mount rigid panels flat on the roof using aluminium brackets. The brackets create about 50mm air gap between panel and roof, which improves efficiency (hot panels are less efficient) and allows water to drain. Each bracket gets sealed with Sikaflex 252 – the same stuff I use for window installations. Four brackets per panel, eight penetrations through my roof, all sealed properly. Haven’t had a leak in 18 months.

The panels connect to each other using MC4 connectors (weatherproof push-together connectors that can only go one way). Then 6mm² solar cable runs from the panels, through a cable gland in the roof, down to the MPPT controller inside the van. Total cable run is about 3 metres on my Ducato.

I’ve seen people use household electrical cable for solar installations. Don’t. Household cable isn’t UV-resistant. I made this mistake in my first build and used some leftover twin-core I had lying about from a house job. Eighteen months later, the insulation was cracked and brittle from sun exposure. Had to replace the entire run with proper solar-rated cable.

Solar Charge Controller (MPPT)

This manages the electricity coming from your solar panels and feeds it to your battery at the correct voltage and current. Without it, your panels would overcharge the battery on sunny days and potentially damage it.

There are two types: PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking).

I used a cheap PWM controller (£35 from eBay) on my second van. It worked. But when I upgraded to an MPPT controller on my third build, I measured 22% more charging current from the same 100W panel in the same conditions. The MPPT is more efficient at extracting power, especially in low-light conditions common in the UK.

Current van uses a Victron SmartSolar MPPT 100/30 (£140 from Amazon). The “100” means it handles up to 100V from solar panels. The “30” means 30A maximum charging current to the battery. For my 350W of solar, this is properly sized: 350W ÷ 12V = 29.2A theoretical maximum.

The Victron has Bluetooth, which sounds like a gimmick but is genuinely useful. I can see exactly how much power the panels are generating, what charge state the battery is at, and historical data showing yesterday’s harvest. When I parked under trees for three days and wondered why my battery wasn’t charging, the app immediately showed “0W from solar” and I knew I needed to move the van.

Nohma stocks the full Victron range and their technical documentation is excellent if you want to understand the algorithms in detail. But for most people, an MPPT rated for your panel wattage plus 25% headroom is all you need.

The MPPT mounts somewhere with decent airflow—these units generate heat when charging. Mine is on the van wall near the battery, secured with self-tapping screws. Solar cable connects to the PV input terminals. Battery cable connects to the battery output terminals. There’s also a small temperature sensor wire that sticks to the battery case—this lets the MPPT adjust charging voltage based on battery temperature.

Battery-to-Battery Charger (B2B)

This charges your leisure battery from your vehicle’s alternator while you’re driving. Critical for avoiding flat batteries after long drives.

My first build used a basic split charge relay (VSR – Voltage Sensitive Relay, about £18). This is just an automatic switch: when it detects voltage above 13.3V from the alternator, it connects your starter and leisure batteries together. When voltage drops below 12.8V, it disconnects them.

This worked fine in my 2007 VW Transporter because it had a traditional alternator that maintained constant voltage.

My second build was a 2019 Ford Transit with a “smart alternator.” Smart alternators vary their output voltage based on engine load and battery state to improve fuel efficiency. The basic VSR spent the entire journey connecting and disconnecting as voltage fluctuated between 12.8V and 14.2V. My battery got partial, interrupted charging. Useless.

From the third build onwards i use a proper B2B charger. This is an active DC-DC converter that takes whatever voltage the alternator provides (could be 12.5V, could be 14.4V) and converts it to the correct charging voltage for your battery type. It doesn’t care what the alternator is doing—it manages the charging profile independently.

I use a Victron Orion-Tr Smart 12/12-30 (£185). It provides 30A of charging current when the engine is running. On a 3-hour motorway drive, this puts about 90Ah back into my battery, which is enough to recover from a weekend’s worth of off-grid usage.

The B2B needs thick cable from your starter battery because it’s drawing high current. I run 25mm² cable over the 4-metre distance from starter battery (under the bonnet) to B2B charger (mounted in the living area near the leisure battery).

Here’s a mistake I made in my second build: I initially used 16mm² cable because “the manual says minimum 16mm².” Four months later, I was getting half the expected charging current. Diagnosis took three weekends of testing. Eventually measured voltage drop: 0.8V lost over the cable run due to resistance. The B2B couldn’t maintain proper charging voltage with that much loss.

Ripped it all out. Replaced with 25mm² cable (cost about £35 for 5 metres from an auto electrical supplier near Chelmsford). Problem immediately solved. Now I always oversize B2B cables – 25mm² minimum for 30A over any distance beyond 2 metres, even if the manual says smaller is acceptable.

The B2B also needs an ignition trigger wire. This is a thin wire (1.5mm² is fine) that connects to an ignition-switched 12V source in your cab. When you start the engine, this wire goes live, which triggers the B2B to start charging. When you turn the engine off, the wire goes dead, B2B stops charging. Prevents your leisure system from draining the starter battery overnight.

Inverter

This converts 12V DC from your battery into 230V AC so you can run household appliances. Optional – I didn’t have one in the first two vans.

In the third van i got a 1000W modified sine wave inverter (£65 from eBay). Modified sine wave creates a stepped approximation of AC power rather than smooth sinusoidal power. It worked for charging my laptop and phone, but my partner’s MacBook charger made a horrible buzzing noise and got hot. Some LED lights flickered. The electric toothbrush charger wouldn’t work at all.

My Ducato uses a pure sine wave inverter (Victron Phoenix 12/1200, £340 from Amazon). Everything works properly. No buzzing, no flickering, no compatibility issues. The extra £275 over modified sine wave is worth it for actually being able to use modern electronics without problems.

1200W output means I can run my laptop (65W), charge two phones (20W total), and still have headroom for more gadgets and appliances. I chose not to run a kettle (2000W) off the inverter because that would require a bigger, more expensive inverter and would hammer the battery – 3 minutes of kettle use pulls about 17Ah from the battery. I use the gas hob for hot water instead.

The inverter connects directly to the battery with 25mm² cable because it can draw over 100A at full output (1200W ÷ 12V = 100A). This cable has a 150A maxi fuse within 300mm of the battery positive terminal to protect it.

I control the inverter with a manual rocker switch mounted on my kitchen unit. When I need 230V power, I flip the switch. When I don’t, it’s off. This matters because even with nothing plugged in, inverters draw 0.5-1A just being turned on. Leave it on for 24 hours and you’ve wasted 12-24Ah for no reason.

The inverter also has an earth terminal that connects to the van chassis with 6mm² cable. This is important for safety—if there’s a fault in a 230V appliance, the current has a path to ground rather than through you.

Consumer Unit (For Shore Power)

If you’re adding 230V shore power capability (so you can plug into campsite hook-up), you need a consumer unit with RCD protection. This is legally required and will save your life if something goes wrong.

I use a 2-way consumer unit from Screwfix (about £48) with a 30mA RCD. It has two MCBs (Miniature Circuit Breakers): one 16A for the ring main that powers 230V sockets around the van, one 6A for a dedicated socket that powers my battery charger.

The consumer unit sits between your shore power inlet and everything else. When you plug into campsite hook-up:

Shore power inlet → Consumer unit RCD → MCB 1 (16A) → Ring main sockets
→ MCB 2 (6A) → Battery charger socket

The RCD monitors for current leakage. If it detects any current going to earth (like you’ve drilled through a cable or a fault has developed), it trips in 40 milliseconds and cuts all power. This prevents electrocution.

I tested this accidentally in the third van. I was drilling a hole for a coat hook and went straight through a buried 230V cable I’d forgotten was there. Big spark, RCD tripped instantly, circuit breaker on the campsite post also tripped. Scared the bollocks off me but I wasn’t injured. Without the RCD, I might have been part of the circuit. That £48 consumer unit potentially saved my life.

Fuse Box and Circuit Protection

Every 12V circuit needs overcurrent protection. If a wire shorts out and tries to draw 100A through a cable rated for 10A, you need a fuse to blow before the cable melts and sets your van on fire.

I use a Blue Sea Systems blade fuse block (about £68 from Amazon). It has 12 individual fused circuits, each with its own blade fuse. One thick cable connects the fuse box to battery positive (via a 100A maxi fuse). All the individual circuits branch off from there.

My fuse allocation on the Ducato

• LED ceiling lights: 5A fuse (actual draw 1.8A)
• LED reading lights: 5A fuse (actual draw 0.6A)
• Water pump: 10A fuse (actual draw 5A peak)
• 12V sockets: 15A fuse (could draw 10A with something plugged in)
• USB sockets: 10A fuse (actual draw maybe 4A with multiple devices)
• Fridge: 15A fuse (draws 4.5A continuous, 8A surge on compressor start)
• Combi Boiler: 15A fuse (draws 8-10A during startup, 0.5-1A running)
• MPPT solar controller: 10A fuse (for the small cable from MPPT to battery)
• Spare circuits: 10A fuses

The high-current stuff (B2B at 40A, inverter at 150A) have separate maxi fuses close to the battery rather than going through the fuse box. You can’t run 150A through a standard blade fuse—they’re only rated to 30A maximum.

Common fuse sizing mistake: People look at their cable size and match the fuse to it. Wrong way round. You size the cable for the load (with voltage drop considered), then size the fuse to protect the actual load, not the cable capacity.

Example: My LED lights draw 1.8A. I used 2.5mm² cable (rated for 20A) because it was a 6-metre run and I wanted to minimize voltage drop. But I use a 5A fuse, not a 20A fuse. If there’s a short in the lights, I want a 5A fuse to blow, not wait until current reaches 20A and potentially starts a fire.

Battery Monitor

This tells you how much power you have left. Without it, you’re guessing.

First two builds had no battery monitor. I’d look at the battery voltage and make assumptions. 12.6V means full, right? Not necessarily. Voltage under load is very different from resting voltage. I ran my battery flat twice because I thought I had more capacity than I actually did.

From the third van onwards i use a Victron SmartShunt (£115 from Amazon). This is a current-measuring device that sits between your battery negative terminal and everything else. It measures every single amp-hour going into or out of the battery and calculates state of charge.

The SmartShunt shows me:

• Battery voltage: 13.2V
• Current draw: -2.8A (negative means discharging)
• State of charge: 76%
• Remaining capacity: 152Ah
• Time to empty: 54 hours (at current draw rate)

This is transformative for actually understanding your power usage. Before the SmartShunt, I didn’t know my fridge drew 2.8A continuously. I assumed fridges cycled on and off like household ones. They do, but the “off” periods are short. Over 24 hours, my fridge uses about 67Ah. Knowing this means I can plan solar capacity and battery size accurately.

The SmartShunt connects via Bluetooth to the VictronConnect app. I can check battery status from bed without getting up. Sounds lazy – it is but it’s also genuinely useful for monitoring how quickly battery drains overnight with just the fridge running.

Installation is straightforward: one thick cable (25mm²) from battery negative terminal to SmartShunt “Battery” terminal. Everything else that needs a negative connection goes to the SmartShunt “System” terminal. This ensures all current flows through the measuring device.

Switches and Controls

Every circuit needs a way to turn it on and off, but not everything needs a manual switch.

Always-on circuits (no switch required):

• Battery monitor – needs to measure 24/7
• Solar MPPT – charges whenever there’s sun, no reason to turn it off
• Fridge – runs continuously, though mine has its own internal on/off

Switched circuits:

• All lighting – obviously needs switches
• Water pump – switched via a small rocker switch on the kitchen unit
• Inverter – manual rocker switch because leaving it on wastes power
• Diesel heater – has its own control panel with thermostat

The B2B charger doesn’t need a manual switch because it’s triggered automatically by the ignition wire.

I use illuminated rocker switches (Blue Sea Systems, about £8-9 each from Amazon) for main systems like the inverter and water pump. They’re sealed against moisture, rated for 20A, and light up when on so you can find them in the dark.

For individual LED lights, I use cheap 12V touch switches (£5.50 for a 5-pack from Amazon). They’re surface-mounted, draw virtually no standby power, and my lighting circuits only pull 1-2A so the switch quality doesn’t matter as much.

Cable and Terminals

This is where most DIY installations fail. Wrong cable size causes voltage drop, overheating, and potential fire. Wrong terminals cause intermittent faults.

Cable sizing isn’t optional. Thicker cables have less resistance. Less resistance means less voltage drop over long runs. Less voltage drop means your equipment gets the voltage it needs to operate properly.

I use a voltage drop calculator (Victron has a free one online) for every cable run. I aim for less than 3% voltage drop on any circuit.

Real example from the Ducato:

• Water pump draws 5A
• Cable run from fuse box to pump is 8 metres
• With 1.5mm² cable: 6.7% voltage drop (unacceptable)
• With 2.5mm² cable: 2.4% voltage drop (acceptable)

I used 2.5mm² cable. Cost an extra £4 over using 1.5mm². The pump now operates at proper voltage and the motor doesn’t work harder than necessary.

My cable inventory:

I buy automotive cable, not household wire. Automotive cable has stranded cores (flexible, handles vibration) rather than solid cores (rigid, will work-harden and break in a moving vehicle).

• 25mm² cable (red and black): Battery to B2B, battery to inverter, starter battery to B2B input. High current, relatively short runs.
• 16mm² cable: Solar panels to MPPT, B2B output to battery. Medium current, medium runs.
• 6mm² cable: Fuse box to high-draw loads like fridge and heater. Medium current, medium-short runs.
• 2.5mm² cable: Most 12V circuits from fuse box to lights, pump, USB sockets. Low-medium current.
• 1.5mm² cable: Very light loads, trigger wires, LED lighting in short runs.

For 230V AC wiring, I use Arctic flex (3-core flexible cable designed for outdoor/low-temperature use). The blue colour makes it easily distinguishable from 12V wiring. I use 2.5mm² for ring mains and 1.5mm² for lighting circuits, which is standard domestic practice.

Terminals and crimping:

Every connection uses proper crimp terminals. No twisted wires shoved into terminals. No solder joints (solder is rigid and will crack under vibration). Proper crimps with proper tools.

I use:

• Ring terminals for bolted connections (battery terminals, busbar connections)
• Spade terminals for push-on connections (switches, some fuse holders)
• Butt connectors for joining two cables end-to-end
• Heat shrink tubing over every crimp to prevent corrosion

The first build, I used a cheap £12 ratchet crimper from Screwfix. Three connections failed in the first year as they were not fully crimped, worked loose with vibration, caused intermittent faults that drove me mental.

Third build onwards, I use a hydraulic crimping tool (cost about £89 from Amazon). It applies consistent pressure every time. I’ve crimped probably 300+ connections with it across two builds and haven’t had a single failure. The extra £77 over the cheap crimper has saved me countless hours of troubleshooting.

After crimping, I slide heat shrink tubing over the connection and shrink it with a heat gun. This seals against moisture and provides strain relief. In a van environment with condensation and vibration, exposed crimps will corrode. Heat shrink adds maybe 30 seconds per connection and prevents problems down the road.

The Actual Wiring Process: Step-by-Step

Right. You’ve got your components. Now you need to connect them without creating a short circuit or a fire hazard. This is the order I follow, developed over four builds to minimize mistakes and rework.

Step 1: Mount Your Battery

Start with the battery because everything connects to it. Choose a location that’s:

• Accessible for checking connections and water levels (if using flooded lead-acid)
• Secured against movement in a crash
• Protected from temperature extremes
• Away from sources of sparks or open flame
• Ventilated (batteries produce hydrogen gas when charging)

My battery sits in a plastic battery box under the offside seating area. The box is bolted to the van floor with four M8 coach bolts that go through the floor and bolt to spreader plates underneath (40mm × 40mm × 3mm steel plate that distributes the load). The battery sits in the box and is secured with two heavy-duty ratchet straps rated for 800kg each.

This might seem excessive for a 23kg battery. It’s not. In a crash, that 23kg experiences forces of 20G or more. That’s 460kg of force trying to break free. The straps and bolts need to handle that or the battery becomes a projectile.

Before connecting anything: Put a piece of tape over the battery positive terminal. You’ll be working near the battery for the next few hours with metal tools. Accidentally bridging positive to the van body with a spanner creates a dead short that’ll weld your spanner to the van and potentially start a fire. The tape is a visual reminder. Remove it last.

Step 2: Install the Battery Monitor (SmartShunt)

The SmartShunt (or whatever battery monitor you’re using) must be the first thing connected to your battery negative terminal. This is critical for accurate current measurement.

Connect the SmartShunt’s “Battery” negative terminal to your battery negative terminal using 25mm² cable (about 300mm length) and a ring terminal. This should be the ONLY connection to the battery negative terminal.

Everything else—all loads, all chargers, all grounds—connects to the SmartShunt’s “System” negative terminal. This routing ensures all current flows through the measuring shunt.

If you connect things directly to the battery negative terminal, bypassing the SmartShunt, the monitor won’t measure that current and your state-of-charge reading will be inaccurate.

Step 3: Create Your Negative Busbar

A busbar is a connection point where multiple cables meet. You need one for negative connections because you’ll have 10-15 different negative wires that all need to connect to the SmartShunt’s “System” terminal, and you can’t fit 15 ring terminals on one M8 bolt.

I use a Blue Sea Systems negative busbar (12-position, about £28 from Amazon). It’s a brass bar with 12 screw terminals, mounted on an insulating base. This bolts to the van wall or floor near the battery.

One thick cable (25mm², about 500mm length) runs from the SmartShunt’s “System” terminal to this busbar. All other negative connections attach to the busbar terminals.

What connects to the negative busbar:

• Fuse box negative feed (6mm² cable)
• Inverter negative (25mm² cable)
• B2B charger negative (6mm² cable)
• Solar MPPT negative (6mm² cable)
• Mains charger negative (2.5mm² cable)
• Any 12V loads that need direct negative connection rather than going through the fuse box (like my fridge and heater)

Label every cable where it connects to the busbar. I use a Brother label maker (about £40, worth every penny) to print heat-shrink labels that go on each cable. “FRIDGE NEG” “MPPT NEG” etc. When you’re troubleshooting at 11pm because something isn’t working, these labels save enormous amounts of time.

Step 4: Install Maxi Fuses on High-Current Positive Feeds

Before connecting anything to battery positive, install fuses on the high-current cables. These fuses must be within 300mm of the battery terminal to protect the cable if equipment shorts out.

The inverter cable (25mm²) gets a 150A maxi fuse. I use an inline maxi fuse holder (about £12 from Amazon) that accepts standard maxi blade fuses. The fuse rating is based on the maximum current the inverter can draw: 1200W ÷ 12V = 100A, plus surge allowance = 150A fuse. The 25mm² cable is rated for 170A continuous, so the fuse will blow before the cable overheats.

The B2B cable (6mm² on the output side) gets a 40A maxi fuse.

The main fuse box feed (6mm²) gets a 100A maxi fuse to protect the cable and act as a master cutoff for all fuse box circuits.

These fuses install close to the battery. On my Ducato, there’s limited space around the battery box, so I mounted a small panel (150mm × 200mm × 6mm plywood) to the van wall with the three fuse holders bolted to it. Cables from battery positive run 200mm to this panel, through the fuses, then continue to their destinations.

Step 5: Connect the Positive Distribution

Now you can remove the tape from battery positive and start making connections.

Three cables connect to the battery positive terminal:

1. Inverter positive (via 150A fuse, 25mm² cable, about 1.5m run to inverter)
2. Main fuse box positive (via 100A fuse, 6mm² cable, about 0.8m run to fuse box)
3. B2B charger output positive (via 40A fuse, 6mm² cable, about 0.6m run to B2B)

I don’t use a positive busbar. Instead, I stack the three ring terminals directly on the battery positive terminal post with washers between them, secured with the terminal nut. This keeps the connection simple and low-resistance.

Make sure each ring terminal is the correct size for your cable. A 25mm² cable needs an M8 or M10 ring terminal. A 6mm² cable needs an M6 or M8 ring terminal. Using oversized terminals means loose connections. Using undersized terminals means you can’t crimp properly.

Torque the battery terminal nut to about 10-12 Nm. Tight enough that the terminals can’t rotate, not so tight that you deform the battery post (especially important with lead-acid batteries where the posts can crack).

Step 6: Wire the Fuse Box

The fuse box now has positive feed from the battery (via 100A fuse) and negative feed to the negative busbar. Time to add individual circuits.

For each circuit, determine the maximum current draw, choose an appropriate fuse (typically 1.5-2× the maximum draw to allow for startup surges), and select cable size based on the cable run length and voltage drop calculation.

My LED ceiling lights draw 1.8A total across six lights. The cable run from fuse box to the first light is 2.5 metres. Using a voltage drop calculator: 2.5mm² cable gives 0.8% drop (acceptable). I installed a 5A fuse and ran 2.5mm² cable.

My water pump draws 3-4A normally, 5A peak when the accumulator tank is empty. Cable run is 8 metres. 2.5mm² cable gives 2.4% drop (acceptable). I installed a 10A fuse.

My fridge draws 4.5A continuous. Cable run is 3 metres. 6mm² cable gives 0.6% drop. I installed a 15A fuse to allow for the 8A startup surge when the compressor kicks in.

Don’t install fuses until you’ve tested the circuit. Run the positive cable from the fuse box output terminal to the load. Run the negative cable from the load back to the negative busbar. Connect everything. Test with a multimeter that you have correct voltage at the load and no shorts. Then and only then install the fuse.

I learned this the hard way in my first build. I installed all the fuses first, then connected all the loads. Somewhere I’d crossed positive and negative on an LED light. When I connected the battery, instant dead short, fuse blew, but I didn’t know which circuit was the problem. Spent two hours disconnecting circuits one by one to find the fault.

Now I test every circuit before installing its fuse. If there’s a problem, I find it immediately.

Step 7: Wire the Solar System

Solar panels on the roof connect to the MPPT controller. The MPPT controller connects to the battery.

Panel to MPPT wiring:

I use 6mm² solar cable (UV-resistant, typically black with a red or blue stripe). This runs from the panels on the roof, through a cable gland in the roof (IP68 rated rubber gland, about £8 from Amazon), down into the van interior, to the MPPT controller.

My two 175W panels are wired in parallel (all positive terminals connected together, all negative terminals connected together). Parallel wiring means the voltage stays the same (around 18-22V per panel) but the current adds (10A + 10A = 20A total).

The panels have MC4 connectors already attached. I use MC4 Y-branch connectors (about £12 for a set from Amazon) to join them: two positive MC4 connectors join into one positive output, two negative MC4 connectors join into one negative output.

The joined cable runs to the roof penetration. The cable gland creates a weathertight seal where the cable enters the van. Critical: the gland must clamp tightly on the cable sheath. If it’s loose, water will track down the cable into your van.

Inside the van, the solar cable terminates at the MPPT controller’s PV (photovoltaic) input terminals. These are screw terminals designed for 2.5-6mm² cable. Positive to positive, negative to negative.

Before connecting solar to the MPPT: Cover the panels with a blanket or park in shade. Solar panels are always generating voltage when exposed to light. You don’t want them powering up during installation—this can damage the MPPT or give you a shock.

Once everything is connected and checked, uncover the panels. The MPPT will detect the voltage and start charging.

MPPT to battery wiring:

The MPPT has battery output terminals. These connect to your positive and negative busbars with 6mm² cable (about 1-2 metre run on most vans).

Positive from MPPT goes to a small 10A inline fuse, then to the positive busbar (or directly to battery positive if you’re not using a positive busbar). This fuse protects the cable from the MPPT to the battery.

Negative from MPPT goes to the negative busbar.

The MPPT also has a temperature sensor cable (thin two-wire cable) that should be stuck to the side of your battery with adhesive. This lets the MPPT adjust charging voltage based on battery temperature—critical for lithium batteries which shouldn’t charge below 0°C.

Configure the MPPT for your battery type using the settings (either via buttons on the unit or via Bluetooth app for smart controllers). AGM, Gel, and Lithium all need different charging profiles. Get this wrong and you’ll either undercharge (battery never reaches full capacity) or overcharge (battery gets damaged).

Step 8: Wire the B2B Charger

The B2B charger has two sides: input (from starter battery) and output (to leisure battery). The trick is routing the input cable from under the bonnet into the living area.

Finding the cable route:

Every van is different, but most have rubber grommets in the bulkhead (the metal panel between engine bay and cab) where factory wiring looms pass through. I look for the largest grommet with some spare space.

On my Ducato, there’s a 60mm grommet on the passenger side with the main wiring loom. I carefully made a 12mm hole through this grommet (using a step drill bit to avoid tearing the rubber) and fed my 25mm² cable through.

Seal around the cable with silicone to keep water and fumes out.

Input side wiring (starter battery to B2B):

Run 25mm² cable from your starter battery positive terminal to the B2B input positive terminal. This cable should have a 60A maxi fuse (in a fuse holder) within 300mm of the starter battery terminal.

On most vans, the starter battery is tucked under the driver’s seat or in a box under the bonnet. You’ll need to remove trim panels to access it. The positive terminal usually has a red protective cover.

I crimp a ring terminal on the cable end, add the fuse holder, then connect to the positive terminal. The terminal post probably already has the main starter cable and possibly other connections (factory wiring for cab electrics). Add your ring terminal to the stack, making sure all terminals sit flat against each other.

Run the cable along the factory wiring routes where possible. Secure it every 300-500mm with cable ties or proper automotive cable clips. Keep it away from hot engine components (exhaust manifolds, turbochargers) and moving parts (drive shafts, steering linkages).

The negative cable runs from a chassis ground point (or starter battery negative terminal) to the B2B input negative terminal. Same 25mm² cable, same routing. I prefer chassis ground because it’s a shorter run—any clean bare metal bolting point on the chassis works. Sand the metal to bright surface, bolt the ring terminal down tight, add a smear of petroleum jelly to prevent corrosion.

Output side wiring (B2B to leisure battery):

Much shorter run. 6mm² cable from B2B output positive to your positive busbar (via the 40A fuse you installed earlier in step 4). 6mm² cable from B2B output negative to the negative busbar.

Ignition trigger wire:

The B2B needs to know when your engine is running. It has a “remote” or “H” terminal (varies by manufacturer) that expects to see 12V when ignition is on.

I use 1.5mm² cable for this. Run it from the B2B remote terminal to your cab fuse box. Most fuse boxes have at least one circuit that’s only powered with ignition on—often labeled “ACC” (accessory) or similar.

I use a piggyback fuse adapter (about £9 for a pack of 10 from Amazon). This clips onto an existing fuse in your cab fuse box and provides a connection point for your trigger wire. Much cleaner than splicing into existing wiring.

When you start the engine, the trigger wire goes to 12V, the B2B powers up and starts charging. When you turn off the engine, the trigger wire drops to 0V, the B2B shuts down. Simple and effective.

Test by starting the engine and checking with a multimeter that the B2B output shows charging voltage (around 14.2-14.6V depending on your settings). If the B2B doesn’t activate, the trigger wire isn’t connected properly.

Step 9: Wire the Inverter

The inverter converts 12V DC to 230V AC, which means you’re working with potentially lethal voltage on the output side. If you’re not confident with 230V wiring, get a qualified electrician to do this part.

DC input (12V side):

Already connected in step 5. The inverter has positive and negative terminals (usually M8 or M10 bolts) that accept ring terminals. Your 25mm² cables (positive via 150A fuse, negative to busbar) connect here.

Make absolutely certain of correct polarity. Positive to positive, negative to negative. Reversing these will destroy the inverter instantly and possibly spectacularly.

Most inverters have a remote on/off terminal. I run 1.5mm² cable from this terminal to a rocker switch on my kitchen unit, then from the switch to battery positive (can tap into any 12V positive source). When the switch is on, the inverter powers up. When off, the inverter is completely isolated except for a tiny microamp drain for the remote circuit.

AC output (230V side):

The inverter has live, neutral, and earth terminals. These are usually screw terminals that accept 2.5mm² or smaller cables.

I run 2.5mm² three-core Arctic flex cable (brown = live, blue = neutral, green/yellow = earth) from the inverter to a double 13A socket mounted on my kitchen unit.

Live terminal to brown wire, neutral terminal to blue wire, earth terminal to green/yellow wire. Every connection gets checked and double-checked. 230V mistakes can kill you.

The socket installation uses a proper back box (25mm or 35mm deep metal or plastic box) screwed to the van wall. The Arctic flex cable enters through a rubber grommet in the back box. The socket front plate screws to the back box.

Earth connection:

The inverter’s earth terminal also needs a connection to the van chassis. This provides fault protection. If a 230V appliance develops a fault and the live conductor touches its metal casing, the current flows to earth through the chassis connection, which blows the fuse or trips the RCD rather than staying live and waiting for you to touch it.

I use 6mm² green/yellow earth cable with a ring terminal. One end bolts to the inverter earth terminal. The other end bolts to a clean bare metal point on the van chassis. I sand the metal to bright surface, bolt down the ring terminal with an M8 bolt and lockwasher, then cover the connection with petroleum jelly to prevent corrosion.

Test the inverter with a low-power appliance first. I use a phone charger (10W). Plug it in, switch on the inverter, check that the phone starts charging. Then try progressively higher loads to make sure everything works.

Step 10: Wire Shore Power (230V Input)

Shore power lets you plug into campsite hook-up to run 230V appliances and charge your battery. This is optional but useful if you use campsites regularly.

Shore power inlet:

I use a standard caravan shore power inlet (about £25-35 from Just Kampers or Amazon). This is a weatherproof socket that mounts flush on the van’s exterior wall and accepts a standard caravan hook-up cable.

The inlet should be mounted on the side of the van you typically park nearest the campsite electrical post. On most UK sites, this is the passenger side (offside). Height is typically 400-600mm from ground—high enough to avoid mud splashing in heavy rain, low enough that you’re not reaching up to plug in.

Cut the hole carefully. The inlet comes with a template showing the required cutout size. I use a jigsaw with a metal-cutting blade. Cut 1mm inside the line, test-fit, then file or sand to final size. Better to go slightly undersize and enlarge carefully than cut too big and have gaps.

The inlet has screw terminals inside (accessed after removing the socket cover). Live, neutral, and earth. From these terminals, run 2.5mm² Arctic flex cable to your consumer unit.

Critical: This cable run must be continuous with no joins or junction boxes. Electrical regulations require unbroken cable from the exterior inlet to the RCD protection. If your cable isn’t long enough, buy a longer piece rather than joining two shorter pieces.

Consumer unit installation:

The consumer unit (about £48 from Screwfix for a basic 2-way unit) mounts on the van wall somewhere accessible but out of the way. Mine is on the wall behind the driver’s seat, about 1.6m high.

The shore power cable connects to the consumer unit’s input terminals (usually at the top of the unit). Live to L terminal, neutral to N terminal, earth to earth bar.

From the consumer unit’s output side (after the RCD and MCBs), you run cables to:

1. Ring main circuit (16A MCB): This feeds standard 13A sockets around the van for running appliances when on shore power. I have two sockets—one in the kitchen area, one near the seating area. The cable runs in a ring: consumer unit → socket 1 → socket 2 → back to consumer unit. This is standard UK domestic practice. Use 2.5mm² Arctic flex.
2. Battery charger circuit (6A MCB): This feeds a single socket that’s dedicated to your battery charger. When you’re on shore power, you plug the charger into this socket. The charger then charges your battery. I use 1.5mm² cable for this circuit because the charger only draws 3-4A.

Testing the RCD:

Once everything is wired, you must test the RCD before using the system. Every RCD has a test button (marked with a T). Press it. The RCD should trip immediately (you’ll hear a click and the switch will move to the off position). If it doesn’t trip, something is wrong and you need to find out what before using the system.

Also test with actual fault conditions: with the system live, deliberately create a small earth fault by touching a piece of wire from live to earth (inside a properly isolated test setup). The RCD should trip in milliseconds.

I tested mine accidentally, as mentioned earlier—drilled through a buried cable. Big spark, RCD tripped instantly, I wasn’t injured. That’s the RCD doing its job.

Step 11: Cable Management

Now you’ve got cables running everywhere. Time to make it not look like a disaster.

I use:

• Plastic cable trunking (D-Line from B&Q, about £8 for 2m) for visible cable runs along walls and under furniture edges
• Cable clips (small plastic clips that nail or screw into place, £5 for 100 from Screwfix) for securing cables to van ribs and hidden areas
• Spiral cable wrap (£7 for 10m from Amazon) for bundling multiple cables together where they run the same route
• Heat-shrink labels (made with a Brother label maker, £40 for the machine plus label cartridges) on every cable end
• Cable ties (hundreds of them, £6 for 500 from Toolstation)

The goal is twofold: make it look tidy and prevent cable damage from vibration.

Route cables away from sharp metal edges. Van bodies have exposed metal ribs, spot welds, and stamped edges that will chafe through cable insulation over thousands of miles of vibration. I use rubber grommets (about £4 for a mixed pack from Amazon) anywhere a cable passes through a metal hole.

Keep 12V and 230V cables separated where possible. They don’t have to be in different areas of the van, but bundle them separately and label clearly. If you’re troubleshooting a fault at midnight, you don’t want to accidentally grab a 230V cable thinking it’s 12V.

Secure every cable at least every 500mm. Unsecured cables will vibrate, work-harden, and eventually crack internally even though the insulation looks fine. I’ve diagnosed mysterious intermittent faults in Build #2 that turned out to be broken conductors inside cables that weren’t properly secured.

Use proper cable clips designed for automotive use, not household cable clips. Automotive clips have rounded edges and rubber cushioning. Household clips are sharp plastic that will cut into cable insulation over time.

Label everything. I label at both ends of every cable: “FRIDGE POS” at the fridge connection, “FRIDGE POS” at the fuse box connection. When you’re tracing a fault, this saves enormous time. Heat-shrink labels are waterproof and won’t fall off like adhesive labels.

Step 12: Testing and Commissioning

Do not assume everything works. Test systematically, starting with the simplest tests and building up to full system operation.

Visual inspection first:

Walk through every connection with a torch and a checklist:

• All ring terminals tight on bolts?
• All crimp connections fully seated?
• All heat shrink in place?
• All fuses correct rating?
• All cables secured and not chafing?
• All polarity correct (red to positive, black to negative)?

I find at least 2-3 issues during visual inspection on every build. Better to find them now than after you’ve connected the battery.

Continuity and resistance testing:

With the battery still disconnected, use a multimeter to check:

1. Continuity: Every circuit should have continuity from positive to its load, and from the load back to negative. Set multimeter to continuity mode (symbol looks like sound waves). Touch one probe to fuse box positive output for a circuit, other probe to the positive terminal of the load. Should beep. Repeat for negative side.
2. Insulation resistance: There should be NO continuity between positive and negative (except through loads like lights or pumps). Set multimeter to resistance mode (Ω symbol). Touch probes to positive and negative of each circuit with the load disconnected. Should read infinity or very high resistance (megaohms). If you read low resistance (less than 1kΩ), you have a short circuit somewhere.
3. Earth continuity: Check that all earth connections have good continuity to chassis. Touch one probe to the earth terminal or cable, other probe to bare chassis metal. Should read less than 0.5Ω resistance.

Initial battery connection:

This is the moment of truth. Double-check everything one last time. Then:

1. Connect the negative cable first. This means connecting the SmartShunt “Battery” terminal to battery negative. Nothing should happen because there’s no complete circuit yet.
2. Connect the positive cables. Have a mate standing by with a fire extinguisher (not joking—if you’ve made a serious mistake, there could be sparks or fire). Touch the first positive terminal to battery positive briefly, watching for sparks. If there are big sparks, stop immediately and find the short.

If there are no sparks or just tiny ones (small sparks are normal from capacitors in electronics charging up), make the connection permanent.

3. Measure battery voltage. Should read normal battery voltage (12.8-13.2V for lithium, 12.6-12.8V for AGM). If it reads something else, investigate before proceeding.

System function testing:

Go through each circuit systematically:

Solar charging:

• Uncover panels (if you covered them earlier)
• Check MPPT shows input from panels
• Verify charging current appears on battery monitor
• Confirm MPPT is in correct mode for battery type

B2B charging:

• Start engine
• Check B2B activates (LED indicator or check voltage at B2B output)
• Verify charging current appears on battery monitor
• Let engine run for 5 minutes, check B2B doesn’t overheat (should be warm but not too hot to touch)
• Turn off engine, verify B2B deactivates

Fuse box circuits: Test each individually:

• LED lights: Switch on, all lights illuminate, check current draw matches expectations
• Water pump: Activate, pump runs, check current draw
• 12V sockets: Plug in a phone charger, verify charging works
• Fridge: Turn on, compressor should start within 1-2 minutes
• Heater: (if fitted) Activate, should start up normally

Inverter:

• Switch on
• Plug in low-power device (phone charger)
• Verify 230V output with multimeter or device works
• Try progressively higher loads
• Check current draw matches expectations (watts ÷ 12V ÷ efficiency)

Shore power:

• Plug into shore power source (or test with a generator)
• Verify RCD doesn’t trip immediately (if it does, there’s a fault)
• Test ring main sockets with appliance
• Verify battery charger activates when plugged in
• Press RCD test button, should trip immediately
• Reset RCD, system should work again

Battery monitor calibration:

If you’re using a SmartShunt or similar, it needs to know battery capacity to calculate state of charge accurately. Configure it with your actual battery capacity (200Ah in my case) and battery type.

The monitor learns over time by observing full charge and discharge cycles. For the first few days, the state of charge reading might not be perfectly accurate. After 2-3 complete cycles (100% to 20% and back to 100%), it calibrates itself and becomes reliable.

Common Mistakes I Made (So You Don’t Have To)

Across four builds, I’ve made every mistake possible. Here are the ones that cost me the most time or money:

Using household electrical cable for the solar run

I had some leftover 2.5mm² twin flex cable from a house renovation. Thought this’ll be fine.” Ran it from the solar panel on the roof to the controller inside.

Eighteen months later, the cable insulation was cracked and brittle from UV exposure. The conductors were starting to show through. I was lucky I discovered it during a routine check rather than when it failed and potentially caused a short.

Lesson: Always use cable rated for the environment. Solar cable is UV-resistant. Automotive cable is vibration-resistant and low-temperature rated. Household cable is neither and doesn’t belong in a van.

Undersizing the B2B input cable

The Victron manual said “minimum 16mm² cable.” I used 16mm² cable. Job done, right?

Wrong. That minimum spec assumes short cable runs (under 1 metre). My run from starter battery to B2B was 4 metres. At 30A charging current, I was losing 0.8V to cable resistance. The B2B couldn’t maintain proper charging voltage with that much voltage drop.

Took me three weekends of troubleshooting to figure this out. I tested the B2B (worked fine on the bench with short cables), tested the battery (also fine), tested the alternator (working normally). Eventually measured voltage at both ends of the cable while charging and found the massive drop.

Replaced with 25mm² cable (£35 for 5 metres). Problem immediately solved. Now I always oversize cables beyond the minimum spec, especially for long runs or high currents.

Not labeling cables

I wired everything up, tested it, everything worked. Six months later, the water pump stopped working. I needed to trace the circuit to find the fault.

Problem: I had twenty-something cables at the fuse box, none of them labeled. I knew one of them was the water pump, but which one? Spent an hour with a multimeter testing continuity on each cable to find the right one.

From third build onwards, every cable gets labeled at both ends. Takes an extra 10 minutes during installation, saves hours during troubleshooting.

Forgetting the MPPT temperature sensor

The Victron MPPT comes with a small temperature sensor that sticks to the battery. It adjusts charging voltage based on battery temperature. I installed the MPPT, got it working, but didn’t install the sensor because “I’ll do that later.”

I never did it later. Forgot about it completely.

The MPPT charged my AGM battery using a default temperature of 25°C. In the Scottish Highlands in February, my actual battery temperature was about 5°C. At that temperature, AGM batteries should be charged at slightly higher voltage (14.7V instead of 14.4V). Without the temperature sensor, the MPPT didn’t know the battery was cold and undercharged it.

I didn’t realize this was happening. I just knew my battery never seemed to get fully charged in winter. Took me a full year to work out why.

Eventually installed the temperature sensor (5-minute job) and immediately saw improved cold-weather charging.

Using cheap crimp terminals

I bought a bulk pack of crimp terminals from eBay. 100 assorted terminals for £8. Seemed like a bargain.

These terminals were made from thin brass that deformed when I crimped them. The crimp tool barrel was also slightly wrong size for the terminal barrels, so I wasn’t getting proper compression.

Three connections failed in the first year. They didn’t fail catastrophically—they were just high-resistance connections that caused voltage drop and intermittent behavior. The heater would sometimes not start. The water pump would sometimes run slowly. Drove me mad trying to diagnose.

Eventually found that several crimp connections were loose and corroded. Remade them all with proper quality terminals (Durite or similar brands from a proper auto electrical supplier). No more problems.

The £8 I saved on cheap terminals cost me probably 10 hours of troubleshooting time. False economy.

Not testing circuits before installing fuses

I mentioned this earlier but it’s worth repeating. In my fourth build, I wired up all the circuits, installed all the fuses, then connected the battery.

Instant dead short. One of the fuses blew immediately. But which circuit was the problem? I had twelve circuits on the fuse box.

Spent two hours disconnecting circuits one by one, replacing the blown fuse each time, trying to isolate the fault. Eventually found I’d crossed positive and negative on an LED light connection.

If I’d tested each circuit before installing its fuse, I would have found the problem immediately with a multimeter.

Now I never install a fuse until I’ve tested the circuit is correct.

Advanced Topics and Optimization

Once you’ve got a basic working system, there are refinements that improve performance and usability.

Battery Capacity Calculations

Knowing how much battery capacity you need saves money and weight. Too little capacity and you’re constantly worried about running flat. Too much and you’re carrying expensive, heavy batteries you never fully discharge.

I calculate backwards from actual usage:

My daily consumption on current build:

• LED lights (6 hours usage): 1.8A × 6h = 10.8Ah
• Fridge (24 hours): 2.8A × 24h (with cycling) = 67Ah
• Water pump (30 minutes cumulative): 5A × 0.5h = 2.5Ah
• USB charging (phones, headtorch, etc.): 2A × 4h = 8Ah
• Combi boiler (6 hours in winter): 1A × 6h = 6Ah
• Miscellaneous (fans, reading lights): 5Ah

Total: approximately 100Ah per day in summer, 120Ah per day in winter.

For off-grid autonomy, I want 2-3 days of battery capacity (for when it’s cloudy and solar doesn’t produce much). That suggests 200-360Ah battery capacity.

But I can’t discharge AGM batteries below 50% regularly. So if using AGM, I’d need 400-720Ah of battery capacity to get 200-360Ah usable.

With lithium, I can discharge to 10% safely. So 222-400Ah of lithium gives me the same usable capacity.

I went with 200Ah lithium because:

• Two full days off-grid in summer without recharging
• One day in winter with heater running
• My solar produces 60-80Ah per day in summer, so I’m net positive even with full consumption
• Lighter and smaller than equivalent AGM setup

But if budget was tight, a 230Ah AGM battery (£340) would give me 115Ah usable, which covers one day’s consumption. Combined with even modest solar, that’s workable for weekend trips.

Solar Panel Angle and Orientation

I mount panels flat on the roof because angled mounting creates wind noise, increases drag, and looks bollocks. But flat mounting isn’t optimal for winter sun collection.

In summer (June-August), the sun is high in the sky. Flat panels work great. I regularly see 80%+ of rated panel output on clear days.

In winter (November-February), the sun is low in the sky. Flat panels see much less direct sunlight. I’m lucky to get 30% of rated output even on clear days.

Tilting panels towards the sun improves winter output by 40-60%. But the faff of adjustable mounting systems, plus the wind resistance when driving, made me decide flat mounting is worth the trade-off.

If you’re planning to park in one place for weeks at a time in winter, portable panels on adjustable stands make sense. You can orient them towards the sun, adjust the angle throughout the day, and pack them away when driving.

For my use case (moving location every few days), fixed flat-mounted panels are simpler and still provide adequate charging combined with B2B charging from driving.

Cable Routing and Vibration Management

Cables in vans experience constant vibration. Over thousands of miles, vibration causes:

• Work-hardening of copper (makes it brittle)
• Fatigue cracking of conductors
• Loosening of screw terminals
• Chafing of insulation where cables rub against metal

The solution is proper securing and strain relief.

I secure cables every 300-500mm maximum. For runs along van ribs, I use plastic cable clips designed for automotive use (these have rubber cushioning). For runs across open spans, I use spiral cable wrap or split conduit to bundle cables together, then secure the bundle.

Where cables connect to equipment, I leave a small service loop (100-150mm of slack cable) before the connection point. This allows the cable to flex slightly with vibration rather than transmitting all movement directly to the terminal.

For heavy equipment (like the inverter or battery), I use cable strain relief glands if the equipment doesn’t have built-in cable clamps. These are rubber grommets that clamp around the cable, preventing the cable weight from pulling on the terminal connections.

Monitoring and Diagnostics

The Victron ecosystem (SmartShunt, SmartSolar, Orion-Tr) all connect via Bluetooth to the VictronConnect app. This provides real-time monitoring of:

• Battery voltage and current
• State of charge
• Solar panel voltage, current, and daily harvest
• B2B charging status and current
• Historical data and trends

This transforms troubleshooting. In second build (before Bluetooth monitoring), if something wasn’t working right, I’d spend hours with a multimeter checking voltages and currents.

In current build, if something’s wrong, I open the app and immediately see what’s happening. Battery not charging from solar? App shows “0W from PV” so I know it’s the panels or the cable, not the MPPT or battery. Fridge draining battery faster than expected? App shows “4.8A continuous draw” and I know the fridge is the problem.

The data also helps optimize usage. I discovered my fridge uses significantly less power if I run it on its lowest setting (maintaining 4°C) rather than maximum cold (attempting to reach -5°C). The lower setting uses 2.8A continuous. Maximum setting uses 4.2A continuous. That’s 50% more power for maybe 3-4°C colder temperature. Not worth it.

If you’re using non-Victron equipment, standalone battery monitors like the SmartShunt (£115) work with any battery and provide similar monitoring capabilities.

Expansion and Upgrades

I design systems with expansion in mind. Even though current van has everything I need now, I’ve included:

• Spare fuse positions (two unused 10A circuits)
• Oversized cable runs (25mm² to inverter even though 16mm² would technically work)
• Empty conduit runs for future cables
• Physical space near the battery for a second battery if needed

This makes future upgrades easier. If I decide to add a built-in microwave (requiring a bigger inverter), I already have the heavy cable in place. If I want to add a second battery for more capacity, I have space and the busbars can accept additional connections.

Planning for expansion costs maybe 5-10% more during initial installation but saves 50%+ on future upgrade costs compared to retrofitting.

Tools You’ll Actually Need

Let me give you a realistic tool list based on what I actually used across four builds, not a fantasy list of everything that might be useful.

Essential tools (can’t do the job without these):

• Multimeter (£15-40): For testing voltage, continuity, and resistance. I use a Fluke 115 (about £150) but a £20 unit from Screwfix works fine for basic testing.
• Crimping tool (£12-90): For crimping cable terminals. Spend the money on a hydraulic crimper (£85-95 range). The cheap ratchet crimpers work but don’t give consistent results.
• Wire strippers (£8-15): For removing cable insulation without damaging conductors. Automatic wire strippers are worth the extra £5 over basic ones.
• Cable cutters (£12-25): For cutting thick cable cleanly. Side cutters or snips work for small cables but won’t cut 25mm² cleanly.
• Spanners/sockets (£20-50 for a basic set): For tightening battery terminals and mounting brackets. M8, M10, and M12 are most common sizes.
• Drill and drill bits (£30-80 for a cordless drill): For mounting equipment and running cables. Step drill bits (£15-25) are excellent for making clean holes in metal panels for cable glands.
• Heat gun (£15-35): For shrinking heat-shrink tubing. A cigarette lighter works in a pinch but takes forever and often burns the cable insulation.

Very useful tools (makes the job much easier):

• Cable fish tape (£8-15): For pulling cables through cavities and conduit. Saves enormous frustration.
• Label maker (£40-60): For labeling every cable. I use a Brother P-Touch with heat-shrink label tape.
• Torch/headlamp (£10-30): You’ll be working in dark spaces under seats and in cupboards. Hands-free lighting is essential.
• Knife/utility blade (£5-12): For trimming heat-shrink, cutting spiral wrap, opening packages, and a thousand other small tasks.

Nice to have tools (useful but not essential):

• Cable lug hydraulic crimper (£40-60): If you’re crimping large terminals (25mm² cables), a dedicated heavy-duty crimper gives better results than a standard hydraulic crimper.
• Voltage drop calculator app: Not a physical tool but essential. Victron has a free one. Prevents undersizing cables.
• Digital caliper (£15-25): For measuring cable diameters and hole sizes accurately.

Don’t bother buying:

• Fancy wire strippers with multiple adjustments: Basic automatic ones work better
• Insulation testers (meggers): Overkill for 12V systems, useful for 230V but a multimeter on resistance mode is adequate
• Cable pulling socks: Never found a situation where these were better than fish tape or just careful pulling

Final Thoughts: What I’d Do Differently on Build 5

I’m already planning Build 5 (full-time van for the wife and me). Here’s what I’d change based on lessons from the first four:

Go lithium from the start. I wasted money on AGM batteries in first three builds that I eventually replaced with lithium anyway. The upfront cost hurts but the performance and longevity make it worthwhile if you can afford it.

Oversize everything by 25%. Battery capacity, solar wattage, cable thickness—I’d spec everything 25% bigger than calculations suggest. The extra cost is minimal and the headroom prevents problems as usage patterns change.

Install the battery monitor first, not as an afterthought. I added monitoring in my third van and wished I’d had it from the first. You can’t optimize what you can’t measure.

Use Victron components throughout. I’ve mixed brands across builds. The Victron ecosystem with Bluetooth integration and VE.Smart networking (where components talk to each other) is worth the premium for the monitoring and control capabilities.

Plan the 230V system properly or don’t bother. Third van had a half-arsed shore power setup that was barely adequate. Current build has a proper consumer unit with RCD protection and it’s transformed how confident I am using 230V appliances. Do it right or don’t do it at all.

Document everything as you go. I drew wiring diagrams for my current build as I installed each component. When I need to troubleshoot or make changes, I can refer to the diagram instead of trying to remember what I did 18 months ago.

But the single biggest thing? Understand the system architecture before touching a wire. The difference between Build 1 (six weeks, three rewires) and Build 4 (eight days, first-time success) wasn’t better skills or nicer tools. It was understanding what I was building and why each component connected the way it did.

That’s what this guide has tried to give you: not just a wiring recipe to follow blindly, but an understanding of how campervan electrical systems work so you can design and build one that suits your specific needs.

Now go wire your van. And when something doesn’t work (because something always doesn’t work the first time), you’ll have the knowledge to diagnose the problem instead of randomly swapping components hoping for a fix.

Affiliate Disclosure: This article contains affiliate links to Just Kampers and Amazon UK. If you purchase through these links, I earn a small commission at no extra cost to you. I only recommend products I’ve tested across my four van builds or would confidently use in build 5. Your support keeps this site independent and ad-free.