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A campervan electrical system is the lifeline to van living. With the right set up for your needs, off grid living can become a reality.
The need to recharge batteries at expensive campsites dwindles, allowing you to take advantage of wild camping with glorious views and still chill a beer or two.
Undertaking a DIY camper van conversion project is quite a challenge though.
The electrical system isn’t just about getting the right batteries and fitting a few solar panels on your roof.
Having figured out how you’ll charge your batteries and bought your campervan appliances, it’s time to get it all installed and whirring.
But how does it all go together?
Understanding the components of a campervan electrical system is critical to a safe installation and for future maintenance while on the road.
This post takes you through every aspect of campervan wiring.
We’ll start with the basics, explaining each component, why you need it and how to choose the right one for you.
It talks about wiring in detail, including choosing the correct size wires and understanding how cable runs affect the overall efficiency of your set up.
We end with a complete guide on how to wire your camper van electrical system, with a definitive list of the tools and materials you need for the job.
But before we get into the nitty gritty, electricity is a serious matter.
Done right, you’ll have a safe set up.
Done wrong, it could lead to injury or worse. There’s loads of often conflicting information available on the internet. So do your research well.
While we’ve installed our own campervan wiring systems a few times now, we’re not qualified electricians and take no responsibility for your installation.
So if in doubt, stop and ask a qualified electrician.
- Parts of a campervan electrical system
- Electrical circuits for your van
- Power source – campervan batteries
- Campervan wires
- Switches, relays, fuses & breakers
- Earth or grounding
- Other installation components
- Circuit commissioning
- Campervan wiring regulations
- When to start wiring your camper
- How to wire a campervan
Parts of a campervan electrical system
Campervan electrical set ups use the basic principles of electricity circuits.
To help explain this, here’s a simplified diagram of an electrical circuit with each component marked.
Below, we’ll talk through each component in simple terms.
Circuit | A circuit is the path or loop through which electricity flows
Power source | The battery bank providing the electricity
Connectors or conductors | A connector is what the path is made from i.e. the wires
Switches | A switch allows the circuit to be opened and closed. When the switch is closed, the circuit is complete and electricity flows
Fuse | A small strip of wire that protects components on the circuit in the event of an electrical surge or increase in voltage
Load | The load refers to the appliances and devices powered by the power source
Earth | A connection to the ground
Sound simple enough?
Before beginning to install any of your electrical system, design your set up and draw out a campervan wiring diagram.
To do this, you need to understand a little about each of these components and so we’ll look at each in turn now.
Electrical circuits for your van
There’s basically 2 types of electrical circuit:
- DC circuit
- AC circuit
Batteries tend to be the main power supply for campervan accessories and appliances.
With a limited amount of stored energy, they do best powering low voltage appliances, even when recharged by solar and main power.
This is why your campervan appliances should be 12v wherever possible.
So, most of the circuits you need in your conversion will be DC circuits.
A DC circuit works by supplying power from the positive terminal of the battery to the negative terminal, via the appliance.
If the circuit is broken by opening a switch, a blown fuse or a disconnected wire, the power flow stops.
AC circuits run on mains electricity, just like in a house.
They’re engineered to operate huge currents so if not handled properly, can cause serious injury or even death.
If unsure of your electrical skills please, please, please seek professional advice.
If you want to charge your campervan batteries from a mains hookup, you need to install an AC circuit.
The simplest campervan AC circuit will have one device: a battery charger.
If going to the effort of installing a battery charger, it’s worth fitting a separate power socket too.
This way, you can power other devices when you’re hooked up to the main supply that would normally be a heavy drain on your batteries.
This is especially useful if you want to use air conditioning units.
Ring main v dedicated circuit
In a campervan electrical system, most of your components should sit on dedicated circuits with a direct line back to the negative terminal of the battery.
This way, if there’s a failure on the circuit, other appliances are unaffected.
There are instances though where a ring main could be an acceptable installation.
A ring main is basically a circuit with multiple components.
For example, Christmas tree lights typically sit on a daisy chain ring main.
They are fitted in direct series, so the output from one light goes directly to the input of the next light and so on throughout the entire string of lights.
If one bulb fails, the circuit is broken and they all fail.
A more common ring main has multiple components spurred off the main ring in parallel. If one component fails, the circuit remains intact so nothing else is affected.
We only recommend ring mains for extremely low current and non essential services.
We have 3 12v LED reading lights on a mains ring circuit in our van. Everything else is on a dedicated circuit.
A short circuit occurs when there’s a breach in the electrical circuit causing current leakage.
This could be caused by a loose wire or faulty installation.
The electricity takes the path of least resistance to the ground and if that path is through flammable material or a person, the result could be fire, injury or both.
Short circuits happen from time to time and to minimise the impact, a fuse or circuit breaker will effectively shut the power supply off.
Power source – campervan batteries
Deep cycle batteries or 12v leisure batteries are designed to release their energy in a steady flow over a long period.
Leisure batteries can withstand hundreds, if not thousands of discharges and recharging cycles, making them ideal for storing energy for your camper van electrical needs.
Battery technology has been evolving for hundreds of years to the point we can now stream movies on our smartphones, powered by ultra thin lithium batteries.
Van lifers can benefit from these advancements in technology too.
We’ve written a complete guide to campervan batteries. That post covers everything you need to know to help you decide the best battery for your lifestyle.
For the purposes of understanding how to wire your campervan, make sure to read our recommended battery installation tips.
A wire is a flexible strand of metal that conducts electrical energy allowing it to flow from one point to another.
The flow of the electrical energy through a wire is called current, measured in amps. It’s this current that is harmful, even deadly.
When you touch a live wire, you will get an electric shock.
If the wire is on an 240v AC circuit, expect to be blown off your feet and land 6 feet under.
On a DC circuit, injury is still possible, though probably not as severe as the AC supply would inflict.
This hopefully illustrates why you need to take care.
Anyway, back to the case in point.
Wires are covered by a plastic sheath. It protects the wire from damage and any conductive element it comes into contact with feeling the adverse affects of the current.
Sizing wires for your electrical system, buying the correct type of cable and planning your cable runs are critical to a successful installation.
Choosing the correct campervan wire sizes
Wire and cable is available in different sizes and using the right sized wire is essential in your camper van electrical build.
If the wire is too small for the amount of current passing through, it will get hot, possibly melting the sheath and burning the wire.
Without protective fuses or circuit breakers you don’t want that touching the side of your van! Note previous warning about injury & death!
Using a larger or over sized wire than needed is much better.
It reduces the chance of cable burn out and makes the electrical circuit more efficient because there’s less resistance.
The total length of the circuit is important in choosing the correct size campervan wires too.
Anything longer than 1.8 metres or 6 foot, particularly in low voltage circuits like those in your campervan, could suffer as much as a 10% voltage drop.
This means your bunk light at the back of your van won’t burn as brightly as the one in the front.
A slightly larger cable will help reduce the voltage drop.
But wiring can become quite costly and unnecessarily more expensive if you use massive wires everywhere.
How to calculate the right size wire
Cable is sold in rolls of dozens of metres so bulk buying the most appropriate size will help keep your conversion costs down.
Step 1 | Determine the current rating (i.e. amps) for every appliance you expect to use in your campervan.
Some appliances will state their rating as watts rather than amps.
For 12 volt components like your fridge, campervan lights and USB phone charger for example the calculation is:
Amps = Watts / 12 volts
unless your running a 24 volt system when you’d divide it by 24 instead of 12.
Some components you use might be 110v, 220v or 240v – like a microwave, TV or cordless drill battery charger.
To use these on your 12v system, you’ll use an AC to DC campervan inverter.
AC power works differently to DC power so the calculation is:
Amps = Watts / (Voltage x 0.8)
Step 2 | Determine the length of the longest circuit you plan to install.
To do this, measure the total distance you’ll lay your cable from the battery to the appliance and back to the battery again.
It’s helpful to use a ball of string to do this, then measure the string length.
Step 3 | Use the table below to determine the cable size you need.
Choose the maximum cable length on the left based on your measurements in step 2 above and the amps based on the highest number calculated in step 1 above.
The standards of wire size and current load are defined in the US by the AWG size and in the UK & Europe by a mm metric scale.
The table below shows both measurements.
* We’ve only noted lengths common for a campervan build.
** The sizes shown will give approx 3% voltage drop rather than 10% with a smaller cable.
Types of electrical cable
Different cables have different purposes and you need to buy the right type for each aspect of your campervan electrical system.
- For DC circuits, use single core cable. These are simple cables with a single wire inside the sheath.
- For the AC circuits, use multi-core cables with at least 3 cores. These are basically cables within a cable like those attached to a lamp plug.
- Solar panel cables tend to be sold as a specific type though in reality, they’re just heavy gauge cables.
- Battery to battery links are heavy gauge – so too thick and expensive to use in the entire DC circuit.
Planning cable runs in a campervan
Even a fairly simple electrical set up uses loads of cable.
We have over 400 metres of campervan wiring in our Mercedes Sprinter van conversion.
To keep the costs to a minimum, it helps to reduce the length of the cable runs where possible.
You can see from the table above a shorter distance needs a lower rated cable.
For efficiency purposes, the table already accounts for inefficiencies and adds a contingency so you only need expect a 3% voltage loss.
Still, aim to keep everything compact and installed as close to each other as possible to minimise the length of cable and so losses.
Lay cables carefully. Avoid sharp corners or areas where the cable may rub and eventually fray.
For belt & braces, fitting conduit to feed the cables through will help avoid these issues.
Cable colours & numbering
You can buy cable in all sorts of colours. For safety reasons, our advice is to stick to the standard colour convention wherever possible.
For DC circuits, the live wire from the battery to the appliance, use red cable and for the negative cable back to the battery, use black.
Sometime the thicker wires are hard to find in red. In this case, buy black and use red electrical tape or heat shrink to mark each end of the live wire.
The colour coding used in AC circuits for wiring your shoreline hookup, varies across the world.
We recommend you fit the standard based on local regulations (more on that below).
As an example, in the UK and Europe:
- Live is brown
- Neutral is blue and
- Earth is green & yellow
where as in the USA:
- Live is black or red
- Neutral is white and
- Protect Ground (Earth) is bare (uncovered), green or green &yellow
A more professional approach is to individually number all cables in line with your design.
When designing your electrical system, place a unique number on each end of the wire in the diagram or schematic.
Use cable numbering collars or tags to identify each wire as you lay it.
This helps enormously when building because it might be several months between laying a cable and installing a component.
If it’s numbered you will instantly know its purpose once you read your electrical schematic.
It also helps in the future if you have to fault find on a circuit.
Switches, relays, fuses & breakers
Fuses, switches and relays all have a different role to play within your campervan’s electrical setup.
The one thing they all have in common however, is they break the circuit.
- Switches tend to break the circuit for operational purposes. So you flick a switch to turn the lights on, closing the circuit.
- Relays are electrically controlled switches.
- Fuses act as a layer of protection. When they receive an unexpected current, they melt, snap and break the circuit. The resulting open circuit can do no harm so it’s effectively a safety device.
- Circuit breakers act as reusable fuses by opening switches. We’ll explain!
A switch is a mechanical lever, that when operated opens or closes the electrical contact and stops or starts the electrical supply.
As with all electrical components, switches have an amp rating indicating a safe current at which they can operate.
You can buy switches to handle massive currents but they get physically bigger and more clunky with a higher rating.
Therefore, it’s important to understand the current demands of your appliances and get suitably sized switches.
For low current uses below about 10 amps like your water pump or lights for example, switches are ideal.
In circuits that have higher currents, there’s a risk the electricity will try to jump or arc across the contacts as they open or close, a dangerous situation for anyone flicking the switch.
In a campervan, there’s a few high current scenarios where dinky switches just won’t do the job safely. A couple of examples are:
- Turning on/off the power to or from the batteries directly.
- Operating appliances that may have a current rating too high for a reasonably sized switch. A coalescer water heater is a good example. Ours draws 18 amps.
In such cases, we need either a large switch or a relay.
In our van conversion, we’ve installed 2 big battery isolator switches. 1 allows us to switch off all incoming charge power from the alternator, solar panels and 240v battery charger.
The other allows us to isolate the battery from supplying any power to any circuit in the van’s living quarters.
So if we were to store the van or ship the van across the Atlantic to South America, we’d isolate everything.
For our coalsecer water heater, we’ve fitted a relay.
A relay is basically an electromagnetic switch.
A small electric current is sent to the relay by flicking a conventional switch. A coil within the relay becomes magnetic, operating a lever to close the main circuit.
So with our coalescer water heater, we flick a switch which send a small current to the relay which in turn closes the high current circuit.
This helps us avoid electrocuting ourselves or having a huge ugly switch in the van.
In camper van electrics, every electrical circuit has a fuse on the live side of the circuit.
A fuse is simply a thin strip of wire in a plastic holder designed to burn out and melt if a current greater than its amp rating passes through.
This breaks the circuit and the appliance stops working, indicating a problem on the circuit or the component it is supplying.
Fuses protect the battery and people from any electrical failings in a component or the electrical circuits.
When designing your campervan electrical system, you need to understand the current each component will draw and install an appropriate sized fuse on the live side of the circuit.
For example, your 12v portable fridge might draw 5 amps and your LED lighting may draw a fraction of an amp.
Put a 5 amp fuse on your fridge (or whatever the manufacturer’s recommendation are) and a half amp fuse or even smaller if you have them on your lighting circuit.
Sometimes a fuse fails because there was a blip in the current somewhere or the fuse failed through age. Replace them and all is well.
However, if it blows again as soon as it’s replaced or when a component is switched on, there’s a problem that needs further investigation.
It could be a faulty appliance, loose wire or a short circuit.
Do not insert a larger rated fuse. The system will not be protected, the fault will still exist and will appear somewhere else at some point.
Worse case, the failing component or your battery could be seriously damaged to the point it burns, melts or catches fire.
A circuit breaker is like a mechanical fuse.
When it senses a current greater than its amp rating, it operates, opening the internal contacts, like a switch.
This immediately stops current flowing through the circuit. Because they’re electro-mechanical, they can be reset – again, like a switch.
It is possible to get circuit breakers for 12v DC setup though because of their relative high cost compared to fuses, they’re not used so often in campervan installations.
However, in mains AC circuits, these are a mandatory component.
They are essential safety devices and must include a fast acting Residual Current Device, (RCD) to prevent electric shocks.
A single pole stops the power supply from the live cable while a double pole RCD stops it from both the live and neutral lines.
The AC RCD breaker will be contained in its own non-conductive container.
We would install double over single pole for a campervan.
Even though the trip will operate and the circuit opened, you wouldn’t be protected from electrical contact on the neutral side with a single pole RCD.
Do not use fuses for any AC installations. Instead always use an RCD.
If you are not sure, seek the services of a qualified electrician.
Earth or grounding
Electricity is naturally drawn to the lowest voltage point around that it can find a path to.
The largest and lowest voltage point around most of us is the ground. The physical ground upon which we stand.
When we create a circuit, the electricity moves from the positive terminal of the battery toward the negative because the negative terminal has a lower voltage.
By keeping the negative terminal as low as possible, preferably zero, the energy will always flow efficiently towards it.
And living in a van full-time, we love an efficient campervan electrical system!
The best way to do this is to attach the negative terminal of the battery to earth.
Now a campervan sits on at least 4 rubber boots – though we have had Mowgli the Unimog on 2 wheels once!
Anyway, we digress. The rubber boots insulate the van from earth so we need to attach the negative terminal to something else.
The next biggest thing around in a campervan is the chassis. So by attaching our earth to the van’s chassis, we keep the voltage at the negative terminal at zero volts.
Perfect for an efficient electrical setup.
Most vehicles are pre-fitted with an earth point. Check with the manufacturer for your make and model to locate it.
In AC circuits your shore power hook up should use the earth connection from the main electrical supply.
When you install your AC circuit, make sure this is connected for your own safety.
That said, there are some countries we’ve visited where the local supply wasn’t connected to a proper earth in their supply.
We noticed when we got occasional electrical tingles and minor shocks from the metal parts of the van. Sometimes even from our laptops!
When in places we’re a little bit suspect of, we check the security of the supplied earth with a multimeter.
If necessary, we connect our chassis to the ground by connecting our battery jump leads from the chassis to a big steel pin we hammer into the ground.
Other installation components
The installation guide below provides a complete list of tools and materials you need to wire your campervan.
There’s a few items on the list worth talking through separately.
A camper van conversion can easily have upwards of 20 circuits.
As each needs a dedicated fuse, for easy maintenenace and replacement, it’s preferable to have all the fuses located together.
A fuse block allows you to hold multiple fuses attached to their circuits in a single location.
A properly mounted fuse block will hold the fuse in place so they don’t fall out as you drive over bumps in the road.
Some fuse boxes distribute the 12v supply via an internal bus bar.
Rather than attach every circuit directly to the battery, it’s easier to install a bus bar to the battery.
Each circuit is then attached to the bus bar rather than the battery making maintenance, installation and future expansion easier.
To choose the right size fuse box and bus bars:
- count how many circuits you have and
- add up the total current of every circuit you plan to connect (so assume everything will be switched on at the same time).
You need a fuse block and bus bar that can handle a current greater than your total and with more fuse holders and terminal connecting points than you have circuits.
They’re not cheap so it’s best to oversize these component to allow for future expansion.
You can buy a combined fuse block and bus bar for easier installation.
Given that you might have a few switches for various campervan appliances, a dedicated switch panel will keep things tidy.
There are many types of switch panels on the markets.
The more expensive include mini 12v breakers or fuse blocks, volt meters, controls, led read outs to control heaters, fans, TVs etc.
Less complex panels allow you to modify and insert your own switch types and meters specifically for your build.
Terminals / connectors
To install the camper’s electrical components into their circuits, most of the wires will need terminals (or connectors) attaching.
Connectors come in all shapes and sizes. You need to fit the correct terminal to the wire depending on the component it’s to be connected to and the size of the wire.
There’s broadly 3 methods of connecting the terminals to the wires:
- Screwed terminals
Which method you choose is down to personal preference. Crimping is cheaper and easier than soldering but we feel the join is more robust when soldered.
We do use crimping but add a spot of solder to the end of the wire first to make it a little thicker so the join is tighter.
We’ve not had any fail yet, even with driving thousands of miles of track in South America.
In camper van builds, the majority of terminals will be crimped connectors with either a metal eye, spay terminal or wire to wire joint.
There’s a set of common sizes of connectors handy to have in your tool kit.
To attach the connectors to the wires, you need a crimping tool.
For large cables, like those you’ll use on your batteries, you’ll need a hydraulic crimping tool to apply enough pressure to attach the crimp.
A solder is the application of melted lead and tin onto the join to create a permanent connection.
This requires a soldering iron and a roll of solder.
A soldering iron is simply a metal probe that heats up the melt solder.
They are usually run off an AC power supply but there are cordless models that use butane gas.
The gas models are better for on the road repairs.
You don’t need any specialised skills to use soldering iron and a bit of practice will help you achieve neat connections.
Top tip | make sure each surface is clean before you start so the solder sticks properly.
This type of connector is a simple hole to insert the wire into and clamp down using a fitted screw or bolt.
You only need to strip a small amount of wire from its sheathing and insert.
Tighten with a screw driver, small spanner or a spring loaded clamp and it’s done.
They make life simple but sometimes they are difficult to get the wire into the connector, or to get a really tight grip on the wire.
Screwed terminals are prone to becoming loose too.
On smaller connections you need a really small flat head screw drive to fix the wires.
Some crimped and soldered terminals don’t have plastic covers so the bare metal presents a shock hazard.
To cover them, we use heat shrink.
Heat shrink is a plastic tube which when evenly heated with hot air reduces in size (shrinks) around the objects it covers.
They’re not especially cheap though.
You could use electrical tape instead but it doesn’t give a tidy finish, isn’t permanent, waterproof or as strong.
In our installation guide below on campervan wiring, we mention circuit commissioning. To keep the instructions simple, we’ll expand on that here.
While installing the components of your circuits, for safety reasons you do not want any power flowing through the wires.
Therefore, never insert the fuse until you’ve fully tested the circuit and ready to let power flow.
Once all the components are installed, carry out your safety checks:
- Physically inspect all connections on the circuit.
- Using a multimeter, check the continuity of the entire circuit. Make sure the fuse is out, the return cable is not connected to the negative battery terminal and the switch is closed.
- With the multimeter again, or better still use an earth tester if you already have one, check there’s no short to earth.
- Do not proceed until you’ve satisfied these tests.
- Open the switch (so the component is off).
- Connect the return cable to the negative battery terminal.
- Insert the fuse.
- Open the switch.
- Check the voltage levels around the entire circuit to make sure there’s no higher than expected voltage drops.
Campervan wiring regulations
Campervan electrical regulations vary from country to country.
In some places, regulations are mandatory and you may experience restrictions on use unless you adhere to them.
In other places, only guidelines are issued.
Regardless, it’s sensible to have someone check over your DIY campervan build, if only for peace of mind that it’s safe and follows best practice.
In the UK, check guidelines on the British Standards with the Caravan Club.
In Canada, RVs need to comply with electrical regulations laid out in each state.
For both the USA and Canada you can get more information on the RV industry association website.
New Zealand and Australia use these regulations.
When to start wiring your camper
Camper van conversions are big projects so at what stage of the build should you start the electrical installation?
The electrical part of the build will start early and finish late so having well thought out plans is key to avoiding re-work and having easy access during the build.
- Have a plan of all the electrical appliances, devices and sockets you want to install.
- Detail exactly where they’ll be physically located in the completed build. Include in this where your batteries, fuse blocks, switch panels, bus bars and earth point will all be installed.
- Look at the cable runs. You may need to make compromises about trying to get the shortest runs.
- Always aim to keep your cable runs inside the van.
- Preferably start all this before laying floors or insulation.
- Consider standardising your cable sizes and connectors, going up a higher current rating rather than a lower one wherever possible.
- You can then begin laying cables before installing the components, ready for connecting at the right time in your build.
- Leave enough extra cable for contingency purposes.
- Begin fitting common components like the fuse blocks, bus bars and switch panels early on.
- Number or tag every end of every cable so you remember what each are for later in the build.
A detailed installation guide for campervan wiring
Campervan wiring can quickly grow into a complex installation but by breaking it down to its component parts, we can simplify it for easier understanding.
The guide below describes how to install the 12v DC circuits in a DIY campervan conversion.
We have separate installation guides for camper solar panels and batteries. Coming soon, we’ll post guides to installing a battery to battery charger and shore power hookup too.
We might even sneak in something on battery monitoring.
Together, they’ll make for one epic installation guide!
- Make sure you fully understand your electrical schematic, incorporating everything you need with extra capacity for future expansion
- Make sure you have access to all the tools and materials you need before you start
- Ideally, fit all components in their operating locations before you begin, follow the manufacturer’s instructions. This isn’t essential but it makes our instructions simpler!
- Confirm cable and connectors are planned sizes
- Check the location of your primary earth point closest to where you’ll fit the battery
- If you haven’t already fitted your components, physically mark their locations and identify where the cables will connect. In tight spaces, use a cardboard template to ensure components will fit before you wire it up
- Identify the cable runs between each major component, looking for the shortest, practical route.
Cable installation preparation
- Install conduit, securing it with cable ties where necessary
- Fit fuse panel (without the fuses) to its operating position as per the manufacturer’s instructions
- Fit positive and negative bus bars to their operating positions as per the manufacturer’s instructions
- Install switch panel to its operating position as per the manufacturer’s instructions
Install battery tray & earth point
- Install battery tray so it’s secure, preferably with bolts. You do not want this to come loose in the event of a collision
- If there is no pre-fitted earth point near your battery tray, fit a bolt securely. This is your new earth point.
- Bolt the braided battery strap to the new earth point.
- Bolt the other end of the braided battery strap to a suitable and clean point on chassis. This needs to be a bare metal spot with no paint, dirt or rust.
- Use a multimeter to check connectivity between the new earth point an existing known earth point, confirming correct installation of the new earth point.
Install battery return cable
- Run black cable from component’s install point, through the conduit, along the planned cable route and to negative busbar
- Attach cable number tags to both ends of each cable
- Trim and attach the negative cable to the component’s negative output cable with a connector secured by a crimp, solder or screwed terminal
- Trim and attach the negative cable to the negative bus bar with the appropriate connectors
- Run cable from negative bus bar to the location where the negative battery terminal post will be, attaching cable number tags to both ends
- Trim and attach one end of the cable to the negative bus bar and attach a connector to the other end, ready for connecting to the battery’s negative post later
If you’re in the enviable position of having all your components installed, repeat this section for all of them at the same time. You already have the black wire on hand and appropriate connectors on hand.
You’ve now installed the negative side of the circuit (without the battery).
We’ll move on to the live side now. This time, we work towards the components from the fuse block.
Install cable from combined fuse block/bus bar to switch panel
- Run red cable from the designated fuse bay to the component’s switch on the switch panel
- Attach cable number tags to both ends of the cable
- Trim each end of the cable, attaching it to the fuse bay and switch with connectors
- Install cable from the switch panel to the component
- Run red cable from the switch to the component’s input terminal
- Attach cable number tags to both ends of the cable
- Trim each end of the cable, attaching it to the switch and component’s input terminal with connectors
If the component isn’t already installed, leave excess wire at the component end for contingency.
Check circuit continuity
Now we’ll check we have a correctly installed circuit from the output of the combined fuse block/bus bar to the negative battery terminal post.
- Check all physical connections on the circuit
- Double check the route through so the cables are attached from the correct fuse bay to the correct switch to the correct component to the bus bar terminal
- Close the switch to make the circuit continuous between these 2 points
- Using a multimeter, check circuit continuity from the output of the combined fuse block/bus bar to the negative battery terminal post. There should be a low reading
Check circuit insulation
- Using the Megga earth tester, attach one probe to output of the fuse bay and the other end to the earth point you installed earlier. There should be no reading, indicating a fully insulated circuit.
Install the battery
If your design calls for more than one 12v battery, check our post on campervan batteries about wiring them in parallel. For simplicity of explaining the instructions here, we’ll only fit 1 battery.
This post is only addressing the DC circuits and not how to charge the batteries. For completeness, we’ve included this section about installing the batteries but for more information, take a look at our article on fitting camper solar panels.
- Fit battery isolator for battery outputs to its operating positions. This will allow you to switch off the entire 12v DC circuit once operational
- Install an inline fuse holder between the battery isolator output and the combined fuse block / busbar.
- Connect one inline fuse holder wire to the combined fuse block / busbar
- Connect the other inline fuse holder wire to the output of the battery isolator switch
- Connect the input wire from the battery isolator switch to a positive battery terminal post connector
- Install the battery into battery tray and secure with battery straps
- Connect a cable from the main earth point, attaching a negative battery terminal connector to the other end, ready for connecting to the battery’s negative
- Take a deep breath, have a cup of tea & relax
Power up the 12v DC circuit
You’re about to release power into your new electrical set up.
- Re-check there are no live wires hanging in your circuits, all negative return cables are attached to the battery negative busbar and the correct polarity is set up so positive circuits and negative circuits do not cross
- Turn all switches on the switch panel and the components to their off positions
- Make sure no fuses are installed
- Check the battery isolators are off
- Attach and secure the battery isolator to the positive battery terminal post
- Attach the negative battery connector from the negative bus bar to the negative battery terminal post
- Attach the negative battery connector from earth to the negative battery terminal post
- Turn the battery isolator to the on position
- Assuming you’ve installed everything safely, there won’t be any sudden flashes, bangs or sparks
- If there are, turn your battery isolator switch to the off position, before testing everything again until you find the fault
- Turn the battery isolator to the off position
- Insert fuse into inline fuse holder between the battery positive terminal post and the combine fuse block / busbar.
- Turn the battery isolator to the on position
- Using a multimeter, confirm you have a reading > 12v between fuse block and earth terminal. A lower voltage may indicate low charge battery or loose battery post connections.
Commission each component in turn
You've installed a 12v DC system with power ready to use.
You are now working on a live electrical system. Take the necessary precautions.
Now we’re ready to switch on each component or appliance in turn.
- Select component to be commissioned
- Check the component is switched off at the switch panel and on the appliance
- Switch battery isolator to the off position
- Insert correct size fuse to the designated fuse bay in the combined fuse block /bus bar
- Switch battery isolator to the on position
- Turn component switch(es) to their on positions
- Thoroughly check component functions as expected
- During each commission step listen, look and smell for any electrical failures such as arcing, burning or buzzing noises.
- If there are, switch the component off, remove the fuse, investigate and repair.
- Repeat the commissioning steps for all components in turn
- Well done! You’ve now successfully installed your campervan DC circuits.
- If you have no electrical experience, seek professional help with your installation
- Avoid routing cables outsider or underneath the vehicle
- Never route 12v DC and 110/240v AC cables in the same cable run or conduit. They must be at least 50mm apart
- The inline fuse amp rating must be sufficiently large to accommodate the total current rating of the circuits running off it
- Battery cables are fairly chunky so use a hack saw to cut these to the appropriate length
- Battery cables with a crimped terminal requires a specialist tool. Pre-made cables are a more simple choice
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