The Complete Campervan Electrical System Guide (2025)

A campervan electrical system is what separates a van with a mattress in it from a home on wheels. Done properly, it gives you reliable power for a fridge, lights, laptop, diesel heater, and anything else you need — completely independently of campsites, for days at a time.

Done poorly, it's a fire risk.

This guide is the complete reference for planning, sizing, and building a campervan electrical system in the UK. It covers every component, how they connect, how to size them correctly, what order to install them in, and what to check before you switch anything on. Each section links out to deeper guides on specific topics — come back here when you need the connecting picture.

Understanding What You're Building

Before specifying any components, it's worth being clear about what a campervan electrical system actually is.

The system has four logical layers:

1. Energy storage — one or more leisure batteries hold the electrical energy your system uses
2. Charging — multiple sources (solar, alternator, mains) put energy back into the batteries
3. Distribution — bus bars, fuses, and wiring route power from batteries to loads
4. Loads — the appliances that use the power

Every decision you make — what battery size, how many solar panels, what wire gauge — is made in service of keeping energy flowing reliably through these four layers.

12V DC vs 230V AC:

Most campervan systems operate at two voltages. The 12V DC system (batteries, solar, DC-DC charger, fridge, lights, diesel heater, water pump) is the core. The 230V AC system (inverter output, shore power, mains charger) is an overlay that provides mains power for appliances that need it.

The two systems must be kept properly segregated and earthed. 12V DC is low enough voltage that even a dead short causes a fire but won't directly electrocute you. 230V AC can kill — it requires the same safety standards as house wiring.

Step 1: The Power Audit

Do not buy any components until you've done this. Every sizing decision depends on knowing your daily energy consumption.

List every appliance you want to run, its rated wattage, and how many hours per day you'll actually use it. Be honest — the fridge runs 24 hours a day; the lights run for 5 hours in the evening; the laptop gets used for 4 hours.

Appliance Wattage Reference

Worked example: standard full-time van build

This is your daily energy budget. Everything else is sized around it.

Key notes on the audit:

• Fridge consumption is the biggest variable. It depends heavily on ambient temperature (a fridge works harder in a hot van), contents, and setpoint. The 45W average for a Waeco CFX35 at 20°C ambient is realistic; in summer heat, budget 60–70W average.
• Diesel heater consumption varies enormously by heater, temperature setpoint, and outside temperature. The 20W average is for a mid-level output once the heater has started; startup power (with glow plug) is much higher but brief.
• Don't forget the loads you barely notice: the MPPT controller, battery monitor, and any always-on electronics all draw a small but continuous current.

Step 2: Size Your Battery

With a daily consumption figure, you can size your battery bank.

The formula:

Required capacity (Ah) = (Daily Wh × days of autonomy) ÷ voltage ÷ depth of discharge

Days of autonomy = how many days you want the system to run without any charging. For most UK van builds, 1–2 days is sufficient when combined with adequate charging.

Depth of discharge = how deeply you're willing to discharge the battery. For LiFePO4: 0.80. For AGM: 0.50.

Example: one-day autonomy, LiFePO4: = (1,855 × 1) ÷ 12 ÷ 0.80 = 193Ah → round to 200Ah LiFePO4

Example: two-day autonomy (UK winter buffer), LiFePO4: = (1,855 × 2) ÷ 12 ÷ 0.80 = 386Ah → 2× 200Ah LiFePO4 in parallel

For the full battery guide including chemistry comparison, UK product recommendations, and installation, see our campervan battery guide.

Step 3: Size Your Charging

You need to replace your daily consumption through your charging sources. The three sources are solar, DC-DC charger (alternator), and shore power.

Solar Sizing

Solar panel output depends on peak sun hours — a location and season-dependent figure. For the UK:

• Winter (Nov–Jan): 0.6–1.5 peak sun hours
• Spring/Autumn (Mar–Apr, Sep–Oct): 2.5–4.0 peak sun hours
• Summer (May–Aug): 4.0–5.0 peak sun hours

Formula: Solar array output (Wh/day) = Panel watts × peak sun hours × 0.85 (system efficiency)

For the example system (1,855Wh/day) in spring (3.5 peak sun hours), to cover all consumption from solar alone: = 1,855 ÷ (3.5 × 0.85) = 624W of panels

That's a lot. Most builds don't try to cover 100% from solar — they accept that in winter they'll supplement with driving or shore power. A more practical 300–400W provides good summer coverage and solid contributions in shoulder seasons.

DC-DC Charger Contribution

A 30A DC-DC charger at 12V delivers 360Wh per hour of driving. For someone driving 1.5–2 hours per day, that's 540–720Wh — meaningful, especially in winter.

Shore Power

A 25A mains charger delivers 300W, charging 200Ah LiFePO4 from 20% to 100% in approximately 6 hours. Shore power is the "emergency" source — used when solar and DC-DC aren't keeping up.

Practical Charging Specification for the Example System

For the detailed charging guide — how to wire each source, sizing specifics, and troubleshooting — see our campervan charging systems guide. For the solar system in depth, see our campervan solar setup guide.

Step 4: Specify an Inverter (If Needed)

Not every build needs an inverter. If all your appliances run on 12V or USB, you can skip the inverter entirely.

You need an inverter if you want to run:

• Laptop (some models require 230V, though most modern laptops charge fine from USB-C)
• Nespresso / bean-to-cup coffee machine (1,000–1,600W)
• Hair dryer or hair straighteners
• Induction hob
• Blender, food processor
• Any appliance with a UK 3-pin plug that has no 12V alternative

Inverter sizing:

Add the wattage of the most power-hungry appliances you'd run simultaneously. The inverter must be rated above this figure.

Always buy pure sine wave. Modified sine wave inverters (cheaper) produce a stepped waveform that damages microprocessor-controlled appliances, causes motor inefficiency, and generates buzz in audio equipment. The price difference (£50–£100) doesn't justify the risk of damaging a laptop. See pure sine wave vs modified sine wave.

Battery capacity check:

A 1,000W inverter at full load draws approximately 95A from a 12V battery (more with efficiency losses). Running a coffee machine (1,100W) for 3 minutes, twice daily, draws: 1,100 ÷ 12 ÷ 0.90 efficiency × (6 ÷ 60 hours) = ~10Ah from the battery per day. Manageable.

Running a 2,000W induction hob for 20 minutes: 2,000 ÷ 12 ÷ 0.90 × (20 ÷ 60) = ~62Ah per cooking session. This requires a large battery bank (300Ah+) and limits how often you can cook inductively without shore power.

For the complete inverter guide, see our campervan inverters guide.

Step 5: Design the Wiring

The Bus Bar Architecture

The standard architecture for a campervan electrical system uses positive and negative bus bars as central connection points. Every charge source and every load connects to the bus bars, not directly to the battery.

[BATTERY (+)] ──── [ANL fuse] ──── [POSITIVE BUS BAR]
                                         │
                          ┌──────────────┼──────────────┐
                          │              │              │
                    [MPPT output]  [DC-DC output]  [Blade fuse box]
                    (Solar)        (Alternator)    (All 12V loads)
                                         │
                          [ANL fuse] ─ [Inverter]
                                         │
                                    [230V loads via RCD]

[BATTERY (−)] ──── [SmartShunt] ──── [NEGATIVE BUS BAR]
                                         │
                          ┌──────────────┼──────────────┐
                          │              │              │
                    [All negative returns from loads and sources]
                                         │
                                   [Chassis earth]

This architecture means:

• A single ANL fuse protects the entire system from the battery
• Adding or removing a component is simple — connect to the bus bar
• The SmartShunt on the negative main cable sees every ampere in and out, giving the battery monitor complete information
• All negatives return to a common point before going to battery — no stray currents through the chassis

Fuse Strategy

Every wire carrying current must be fused at the power source end within 300mm. This protects the wire, not the appliance.

Main system fuse (ANL): Sized to the main cable's current capacity (see cable sizing table in our wiring guide).

Inverter fuse (ANL): Inverters draw very high current on the 12V side. A 1,000W inverter needs its own ANL fuse — typically 100–125A — between the positive bus bar and the inverter input.

Individual circuit fuses: The fuse box (blade fuse holders) fuses each 12V circuit individually. Size each fuse to the circuit's cable, not its load.

DC-DC charger and MPPT fuses: Each charger's output cable should be fused within 300mm of the bus bar connection.

Cable Sizing: The Fundamentals

Wire gauge in the UK is specified in cross-sectional area (mm²). The two factors that determine required cable size are current (amperes) and cable length.

Why length matters: Resistance increases with cable length. A wire carrying 10A over 5m has more voltage drop than the same wire over 1m. Excessive voltage drop wastes energy and can cause loads to malfunction (a 12V fridge receiving 11.2V may not run correctly).

Target: Keep voltage drop to under 3% at maximum expected current (0.36V on a 12V system).

Keep inverter cables as short as possible — the high current means every extra centimetre adds meaningful voltage drop and heat.

For the complete wiring guide including the voltage drop calculation formula and a full cable sizing table, see our campervan wiring & safety guide.

Step 6: Plan the 230V AC System

If you have an inverter and/or shore power, you have a 230V AC circuit. This requires:

RCD protection: A 30mA Type A or Type F RCD immediately after the shore power inlet and/or after the inverter output. This is non-negotiable for safety.

Consumer unit: A small consumer unit (or just a standalone RCD+MCB) distributes 230V power to sockets with individual MCB protection per circuit.

Earth arrangement:

The 230V neutral-earth bond must be handled correctly. On shore power, the site provides the earthing. On inverter power, the inverter's output earth must be bonded to the vehicle chassis. Some inverters (Victron MultiPlus) include an internal transfer relay that manages this automatically. For separate inverters and shore power systems, you need to ensure the correct bond is active in each mode — this is where a properly specified consumer unit helps.

230V wiring: Use 2.5mm² three-core (brown, blue, green/yellow) flex for all 230V circuits. Minimum. Never use 1.5mm² for 230V circuits in a campervan.

Socket placement: Keep 230V sockets away from the kitchen splash area and shower. Use non-standard positions (don't put them at floor level where water pools).

The Complete Component List

For a mid-range full-time UK campervan build (1,800–2,000Wh/day):

Energy storage:

• 200Ah LiFePO4 battery (Fogstar Drift 230Ah or Victron SmartLithium 200Ah)
• Victron SmartShunt 500A battery monitor

Charging:

• Victron SmartSolar MPPT 100/30 charge controller
• 300W solar panels (2× 150W rigid, or 3× 100W)
• Victron Orion-Tr Smart 12/12-30A DC-DC charger
• Victron Blue Smart IP22 12/25A mains charger
• 16A CEE17 shore power inlet

Distribution:

• Positive bus bar (Blue Sea, Victron, or custom copper bar)
• Negative bus bar
• ANL fuse holder + 150A ANL fuse (main battery fuse)
• ANL fuse holder + 100A ANL fuse (inverter)
• 12-way blade fuse box (for individual circuits)
• RCD (30mA, double-pole)
• Consumer unit or MCB for 230V circuits

230V AC:

• Victron Phoenix 1000W or 1600W pure sine wave inverter (if needed)
• 230V sockets (2–3)

Wiring:

• 35mm² cable for battery main positive/negative leads (1–2m)
• 35mm² cable for inverter leads (0.5m)
• 10mm² cable for MPPT, DC-DC, and mains charger runs
• 2.5mm² automotive cable for most 12V circuits
• 1.5mm² automotive cable for light circuits
• 2.5mm² three-core flex for 230V circuits
• Ring terminals, heat shrink, cable clips

Tools:

• Ratchet crimper (Knipex or similar) — not a cheap crimper, this matters
• Wire strippers
• Multimeter
• Clamp meter (optional but very useful)
• Drill and hole saws (for panel penetrations)

For detailed component selection by budget, see campervan electrical parts list.

Budget Breakdown

These are hardware costs only; they don't include the shore power inlet, consumer unit, crimping tools, or installation time. Add £100–£200 for those.

The "premium" figure for a full Victron ecosystem build — where every device talks to every other device, monitored remotely via the Victron VRM app — is well justified for full-time van life where the system must be reliably self-managing.

Wiring Order: How to Connect Everything Safely

The order in which you make connections matters. Connecting in the wrong order can cause sparks, blown fuses, or damaged components.

Recommended sequence:

1. Mount all components but don't connect anything yet
2. Run all cables, leaving ends unconnected at both ends
3. Connect all negative cables (no current flows on negative-only connections)
4. Connect all positive cables except the main ANL fuse — connect all positive bus bar feeds, MPPT, DC-DC output, fuse box, inverter, but leave the battery-side connection unfinished
5. Do a pre-power check: verify all connections are tight, polarity is correct, the ANL fuse is NOT yet inserted
6. Connect solar panels to MPPT controller (do this with panels covered if possible; the MPPT won't have a battery to regulate against yet so leave this until battery connection is made)
7. Insert main ANL fuse — the system is now live. The battery connects to everything via the bus bar.
8. Check bus bar voltages with multimeter
9. Switch on each 12V circuit one by one and verify
10. Start engine — verify DC-DC charger starts (Victron Connect app will show "Bulk" or "Absorption")
11. Connect to shore power (if available) — verify mains charger starts, test RCD

Common Mistakes (And How to Avoid Them)

Not doing a power audit first: The most common mistake. People buy a 100Ah battery because it sounds like enough, then discover it runs out in 8 hours. Start with your power audit; let it determine the battery size.

Using the wrong wire gauge: Undersized wires overheat. Oversized wires are wasteful and expensive. Follow the sizing table; don't guess.

Forgetting the shunt: A battery monitor without a shunt is useless. The shunt goes in the main negative cable. If it's missing or bypassed, the monitor can't count amps.

Not fusing close enough to the source: The 300mm rule applies to every positive cable. The fuse must be within 300mm of where it taps off from the bus bar or battery — not somewhere in the middle of the run.

AGM charger settings on a LiFePO4 battery: Setting your MPPT or DC-DC charger for AGM (which applies 14.4–14.7V absorption and an equalisation charge) slightly overcharges LiFePO4 and causes long-term capacity loss. Configure every charging device for LiFePO4 specifically.

Skipping the RCD on 230V circuits: The RCD is what prevents electrocution. A fault in 230V wiring without an RCD is potentially fatal. This is not optional.

Mixing battery chemistries: Connecting a LiFePO4 and an AGM battery in parallel causes dangerous equalisation currents. Never mix chemistries.

Using soldered connections instead of crimped: Solder joints can develop cold cracks from vibration and lose conductivity. Properly crimped ring terminals are the correct method — use a quality ratchet crimper, not a cheap one.

Running inverter cables too long: Inverter cables carry enormous current. Every extra 10cm of cable at 100A or more is meaningful resistance. Mount the inverter close to the battery; keep cables under 1m where possible.

Choosing Your Van: Electrical Considerations

The choice of van affects your electrical build in practical ways:

Roof area: More roof space = more solar. A long-wheelbase high-roof Sprinter or Transit can carry 600–800W of rigid panels. A short-wheelbase low-roof Transit Custom might manage 150–200W.

Alternator type: Check whether your specific model has a conventional or smart alternator. Transits from 2016+, Sprinters from 2018+, and Ducatos from 2015+ typically have smart alternators — use a DC-DC charger.

Battery placement: The location of the existing starter battery affects DC-DC charger cable runs. Some vans (Transit) have the starter battery in the engine bay; others (some Sprinters) have it under the driver's seat, which simplifies the DC-DC input run.

Existing wiring: Some vans come with an OEM leisure battery prep or an auxiliary battery system. These can sometimes be integrated into your build, though they're often limited in capacity. Check what's there before duplicating it.

For van-specific guides:

• Ford Transit campervan electrical guide
• Mercedes Sprinter electrical system guide

12V vs 24V: When to Upgrade

Almost all campervans use 12V systems. 24V is worth considering only when:

• Your battery bank exceeds 400Ah (at higher capacity, the current advantages of 24V — thinner cables, less voltage drop — become meaningful)
• Your inverter exceeds 2,000W continuous (at 24V, a 2,000W inverter draws ~90A; at 12V it draws ~185A)
• You're using a large solar array (400W+) where the 24V string voltage fits MPPT input voltage better

The disadvantage of 24V: all your 12V loads need a DC-DC converter down to 12V. Fridges, diesel heaters, and lighting all run at 12V — at 24V you need an additional step-down converter for each category. This adds cost and complexity.

For most van builds under 300Ah, 12V is simpler and the right choice. See 12V vs 24V campervan systems for the full analysis.

The Victron Ecosystem: Is It Worth It?

Victron Energy products have become the standard reference for quality campervan electrical components. The solar MPPT controllers, DC-DC chargers, inverters, battery monitors, and battery management systems all communicate with each other via Bluetooth and their proprietary VE.Bus/VE.Direct protocols.

What ecosystem integration provides:

• Accurate state of charge: The MPPT knows the battery voltage, the SmartShunt knows how many amps are flowing, and the battery (if Victron SmartLithium) reports its own SoC. Combined, the system knows exactly how full the battery is.

• Adaptive charging: If the battery is cold (below 5°C), the Victron chargers automatically reduce charge current to protect the cells — without you having to intervene.

• Remote monitoring: Cerbo GX (Victron's communication hub) connects to the internet via WiFi and uploads data to Victron's VRM portal. You can see battery SoC, solar production, and charger status from a web browser or mobile app from anywhere in the world.

• Automatic power management: MultiPlus inverter-chargers can automatically switch between inverter and shore power, manage transfer switching, and implement battery protection cutoffs that the system enforces automatically.

The downside: premium pricing. A full Victron ecosystem (SmartLithium battery, SmartSolar MPPT, Orion XS DC-DC, MultiPlus inverter-charger, Cerbo GX) for a 200Ah 12V system will cost £3,000–£4,000 in components alone. A well-specified non-Victron system using quality alternatives (Fogstar battery, EPever MPPT, Sterling DC-DC) costs £1,200–£1,800 and works well.

For full-time van life where you depend on the system daily and want to monitor it remotely, the Victron premium is justified. For a weekend van or budget build, quality alternatives are entirely adequate.

Safety: What Can Go Wrong

Electrical fires: The most serious risk. Causes:

• Undersized wire overheating under load
• A short circuit on an unfused positive cable
• Corroded connections with high resistance generating heat
• A shorted battery terminal touching the van body

Prevention: size every wire correctly, fuse every positive wire within 300mm of the source, use crimped connections with adhesive-lined heat shrink, use battery terminal covers.

Electrocution: Only possible on the 230V side. A 30mA RCD disconnects within 30ms of a leakage current — before it can cause cardiac arrest. Never work on 230V circuits with the RCD removed. Always use a socket tester to verify polarity and RCD function after installation.

Battery gas: LiFePO4 produces no hydrogen gas (unlike flooded lead-acid) and doesn't off-gas under normal conditions. A very serious internal fault in a LiFePO4 battery can produce electrolyte vapour, but this is extremely rare with quality batteries. AGM batteries can produce small amounts of hydrogen during heavy charging or equalisation — adequate ventilation is important.

BMS failure: If a battery's BMS fails, the battery may not protect itself. Signs of BMS failure include: battery that won't accept charge or deliver discharge at all, battery that discharges but doesn't protect against over-discharge. A battery showing these symptoms should be disconnected and replaced or repaired.

See our dedicated safety guide: campervan electrical build checklist for the complete pre-commissioning verification process.

Related Guides

• Campervan battery guide — sizing, types, and installation in depth
• Campervan solar setup guide — panels, MPPT controllers, and optimisation
• Campervan charging systems guide — DC-DC, shore power, and multi-source management
• Campervan wiring & safety guide — cable sizing, fuses, and earthing
• Campervan inverters guide — 230V power from your battery

FAQ

How long does it take to install a campervan electrical system?

For a competent first-timer, a mid-range system (200Ah battery, 300W solar, DC-DC charger, mains charger, inverter, 8 circuits) takes 4–6 full days. The wiring, crimping, and route planning take the most time. Experienced builders complete the same system in 2–3 days.

Do I need 12V or 24V for my campervan?

12V is standard and correct for the vast majority of campervans. Only consider 24V if your battery bank exceeds 400Ah or your inverter exceeds 2,000W continuous.

Can I do this myself, or do I need an electrician?

The 12V DC system is entirely DIY-able with proper research and planning. For the 230V AC system, we recommend having a qualified electrician inspect your work before use — not because it's legally required (campervans aren't subject to Part P), but because a 230V fault can be fatal and an expert's review costs less than the consequences of getting it wrong.

What's the most important safety item?

The ANL fuse within 300mm of the battery positive terminal. A short circuit on an unfused cable connected to a LiFePO4 battery can deliver thousands of amps — enough to melt copper instantly and start a fire. This fuse is what stands between a minor wiring fault and a van fire.

Is a second-hand caravan electrical system suitable for a van conversion?

Caravan electrical systems are 12V DC (usually, with 230V hook-up) and use similar components. However, caravan wiring is often undersized by campervan standards (campervans draw more sustained current), the batteries are often well-used, and caravan chargers may not support LiFePO4. Salvage individual components that are in good condition; don't assume the whole system is suitable as-is.

How much does a campervan electrical system cost?

Budget builds using basic components: £400–£700. Mid-range builds (LiFePO4, MPPT, Victron DC-DC, decent inverter): £1,000–£1,800. Full Victron ecosystem: £2,500–£4,500+. These are hardware costs; add £100–£300 for wiring materials, terminals, and tools if you don't have them.