Van wiring and electrical will possibly be your biggest expense and biggest frustration during your van build. But with a little knowledge and effort almost anyone can tackle the challenge. This topic is extremely in depth so we’re breaking it into multiple parts. Buckle up we’re about to get nerdy. Remember, it’s perfectly okay to outsource the wiring of your van to a professional or have a professional inspect your work. We are not professional electricians so take our advice with healthy skepticism. This post contains affiliate links, we earn from qualifying purchases at no cost to you.

This post will cover the basic fundamentals you need to know such as how to choose the appropriate wire type and size, how to terminate your wire, how to choose fuses and switches, how to protect your circuits and much more. Use the list below to jump to specific topics. You can find links to all the components we used in our build in the van build shop.


Basic Electrical Terminology

AC/DC

We’re not talking about the rock band šŸ¤˜. AC and DC stands for alternating current and direct current respectively. This has to do with the way electrons move though the conductor and brings up the topic of polarity. All batteries are DC and anything that is directly wired to your battery will be DC such as LED lights, USB outlets, your water pump, etc. Anything that you plug into a typical wall outlet in a house will be AC like an electric kettle, your laptop charger or electric coffee grinder. You will most likely have both AC and DC in your van but this post will mostly cover DC. If you want to learn more about inverters, head to this post.

Credit: http://www.freeingenergy.com

Polarity

In a DC circuit, current flows in one direction only, one pole is always negative and the other pole is always positive. In an AC circuit the two poles alternate between negative and positive and the direction of the current reverses periodically. The positive (+) wires in a DC circuit will be RED and the negative(-) wires will most likely be BLACK but can sometimes be WHITE. It’s important not to cross up the polarity of your wiring. Wire used in AC applications will often have three colors, black, white and green. Black is the phase wire or ‘hot’ and will connect to brass terminals. White is neutral and will connect to silver terminals. Green is earth or ground.

Volts, Amps, Watts & Ohms

Volts (V) measure potential difference. Amps (A) measure electrical current. Watts (W) measure power and Ohms (Ī©) are a measure of resistance. WATTS = AMPS X VOLTS. This is a formula you will need to use when calculating the gauge (size) of wire to use in your circuits. This website has a handy calculator for you to use, just enter two of the known variables to get the others.

Wire Gauge

Gauge refers to the cross sectional area of wire and is standardized by American Wire Gauge (AWG) guidelines. The larger the gauge the more amps the wire can handle. Different electronics will require different gauge wires depending on their amp draw. The gauge is denoted by a number ranging from 000(very large) to 36 (very small). Remember the Watts = Amps x Volts from earlier – this is what we will use to determine the correct wire gauge for your circuit. There is no reason not to over size your wire (besides cost) but under sizing your wire is a good way to start a fire.

Parallel vs Series Circuits

You might remember this from middle school science class. In a series circuit, the different components in the circuit are wired in a daisy-chain so that one inputs negative is connected to the next inputs positive and so on. In a parallel circuit the different components each have their own branch. Every device must function in a series circuit for the circuit to be complete. If one bulb burns out in a series circuit, the entire circuit is broken. In parallel circuits, each light bulb has its own circuit, so all but one light could be burned out, and the last one will still function.

Credit: stickmanphysics.com

In a series circuit the amps are constant and volts get changed based on the individual components in the circuit. In a parallel circuit the opposite is true, voltage is constant and amps are changed based on the individual components.


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Wire Type

Not all wire is created equal and it’s not an area where you want to cut corners in my opinion. When purchasing wire there are a few things to look for. First, for vehicle applications, stranded wire is preferred over solid core wire (such as Romex). Stranded wire is made to handle the vibrations in a vehicle and is more flexible. Second, make sure your stranded wire is OFC (oxygen free copper) wire not CCA (copper clad aluminum). CCA wire is aluminum with an electroplated layer of copper on top while OFC wire is pure copper. Don’t cheap out here, stick with stranded OFC like this.

Stranded vs solid wire – Stranded is better for vehicle applications

Wire Gauge

Correct gauge of wire depends on two things; amp load and length of circuit. For example, your fridge will draw more amps than your lights and therefore will require a larger gauge wire. The distance between your fridge and batteries will also help determine the correct gauge because the farther electricity has to travel the more the voltage drops (this really only applies to DC circuits, and the distance is measured ’round trip’ as an electron is concerned, so you have to double the actual wire length).

Each electrical component you purchase will have an amp rating or wattage on the package or part. Remember to use this calculator to convert from amps to watts and vice versa. For example lets say your water pump draws 7.5 amps when running and that the total length of wire we will need to complete the circuit (switch included) will be 30 feet. Using the chart below we can see that a 14 gauge wire will handle 10 amps in a 30 foot circuit so this will be more then enough in this case.

Credit: http://www.bluesea.com

For simplicity sake, I recommend running only one gauge wire throughout your whole van build. With exceptions for high amp devices such as the fridge, water pump or heater which you want to run a larger gauge for. We found that 16 gauge wire met all the demands of our circuits except our fridge, where we choose to use 12 gauge. Just look at the individual amp draws for each of your electrical components and go from there. We cover how to start designing your wiring diagram here.


Fuses & Circuit Breakers

Fuses are an engineered weak point in a circuit that protect against over current. They are designed to blow when too much current passes though them preventing damage to wires and electrical components. Every circuit in your van should have its own fuse. Fuses are meant to protect the WIRE not the load, so therefore choosing the correct fuse for each circuit is pretty easy, or is it?

If the wire you used is over sized for the circuit, for example 16 gauge for an LED light circuit that will carry 2 amps, and you use a 25 amp fuse because that’s what the wire will handle, the lights will be damaged before the fuse blows in an over current situation. To choose the correct fuse, we need to consider the smallest gauge wire in the whole system, and sometimes that is actually inside the component you installed. For example the puck lights in our ceiling had very thin, probably 20 gauge, wire coming out of them from the box. The fuse for that circuit then should be for 20 gauge wire, not 16. Fuses should be installed on the positive side of your wiring, well talk about fuse blocks in the next section.

There is a formula for working out the fuse rating. First calculate the total amps used by all appliances in the the circuit you want to fuse. Then multiply that number by 1.25. That is the size fuse you should use. For example, if you have a circuit with two strips of LED lights (2.5 amps each) and two USB ports (.5 amps each), this circuit could see 6 amps when operating normally. 6 x 1.25 = 7.5, this is the correct fuse for this circuit.

Circuit breakers do the exact same thing as fuses but they are meant to be reused instead of replaced. Because vehicles are subject to vibration, circuit breakers are not recommenced because a big enough jolt could cause the breaker to trip. Keep it simple and stick to fuses. The only exception to this is on your solar panels, you can find more information here.


Fuse Blocks and Bus Bars

Fuse blocks and bus bars are ways to make power distribution easier. Instead of hooking all your circuits directly to the terminal of your battery, you would instead use a fuse block or bus bar to manage the load. I recommend the Blue Sea Systems fuse block. It can handle up to 12 individual circuits each with their own fuse and it has an integrated ground bus bar. You can also label each circuit on the cover so you don’t forget what’s what.

Fuse block with integrated ground (-) bus bar
Positive bus bar

Protecting Your Wire

Whenever possible, protect your wire with loom or conduit. Try to avoid running bare wire though metal tunnels such as the ribs of your van. Conduit/loom will protect your wire from chafing which could eventually lead to a short. One caveat is you can run direct bury DC wire, it is meant to be buried in the ground without conduit. It has its own sheathing. It is more expensive and harder to work with because it is stiffer but it is great quality wire especially for outdoor application such as exterior lighting.

split plastic loom
conduit

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Grounding

When working with DC you have the option of connect all your negative wires directly to the metal of your van to complete the circuit and this is exactly how the manufacturer of your van does it. Electrons are little gremlins however and we personally do not recommend using the metal of your van as ground when doing your electrical. Instead, run all your negative wires back to the battery compartment and use a bus bar or fuse block to connect them to the negative terminal of your battery. This will insure that your electrical system and the vans electrical system are completely separate from one another potentially preventing issues such as galvanic corrosion while making diagnostics easier.


Terminating Your Wires

Eventually you will have to terminate your wire, this will either be at your fuse block, your switch, or your appliance. For small gauge wire, you will most likely want to use either a ring terminal or spade connector. Ring terminals are great when the wire can be secured with a screw and spade connectors are best for connecting two ends of wire together. Butt connectors are used when you want to join two wires together permanently. Terminals are color coded for the correct wire gauge, seen below.

  • Red = 18-22 AWG
  • Blue = 14-16 AWG
  • Yellow = 10-12 AWG

Crimp vs. Solder

For automotive applications where vibration is a concern, crimping is the gold standard. Soldered joints are prone to breaking because the process of soldering causes the wire to become ridged and brittle. A properly crimped joint remains flexible and easier to perform then a soldiered joint.

How to Crimp and Heat Shrink

To get a proper crimp we recommend investing is a quality crimping tool such as this one, it will serve you for the rest of your life. You want to strip the plastic sheath off your wire so that it fits in your terminal with only enough wire exposed to provide a good crimp. I personally don’t like the colored plastic sleeves that come preinstalled on terminals. It’s impossible to actually see your crimp and they don’t look good after they’ve been crimped. Instead I prefer to remove the sleeve and use heat shrink to cover the exposed crimp like in the images below. This is just a preference but it allows you to have more control over the entire process.

Before you put your terminal on, slide heat shrink up the wire. If you forget to put heat shrink on, you may struggle to get it on after the terminal is crimped. A good crimp will result in a single fused metal so you need to press pretty hard. It is possible to over crimp which causes the metal to break, this is most common with the red 22 gauge terminals and another reason I like to remove the color sheath to visually inspect the crimp. Always check your crimp by tugging on the wire and terminal. If the terminal comes off you need to redo your crimp.

Once you are confident that you have a good crimp, you are ready to heat shrink. Use the appropriate size heat shrink for your wire. Use red heat shrink for positive wire and black heat shrink for your negative wire. The heat shrink should cover any exposed wire and the crimp section of your terminal, only where your terminal is contacting your source should metal be exposed. If at all possible, don’t use an open flame like a lighter when using heat shrink. A flame can burn your heat shrink and leave black residue, instead use a heat gun or, my favorite tool, butane torch. Good heat shrink has an adhesive on the inside with a marine grade sealant which will help prevent corrosion in the future and it looks super pro.

Terminating Heavy Gauge Cable

Large gauge cables, such as the ones you’ll use on your battery, will also be terminated with a crimp connector called a lug. Just like purchasing OFC wire, you want to make sure to get pure copper lugs, instead of aluminum. The lugs shown below are called ‘flared starter lugs’ and you want to make sure the tool used for crimping is compatible with the type of lug you have.

The lugs will be stamped with two sets of numbers. On the photo to the left the numbers are 2-3/8. The number 2 refers to the gauge wire this lug is meant to be used on and the 3/8 is the diameter of the hole in inches. When buying lugs, (which are not cheap) make sure to pay attention to both of these numbers so you don’t end up with the wrong size. Here’s a link to an assortment of lugs.

To crimp these copper lugs the process is the same, it just requires bigger tools. You will need a lug crimper such as the ones below. The first tool on the left is meant to be struck with a hammer. I haven’t used one of these before so I cant speak to its effectiveness, but they seem to have pretty good reviews on Amazon. The tool on the right below is lever action and has a set of rotating dies that will accommodate the most common sizes of lugs. You just need to match the dies to the size of lug you’re crimping and press down on the handle as you would with bolt cutters. This is the style of lug crimper I’m familiar with and it worked well enough, although there is a technique that requires some practice to get right. Just go slow and watch how the die is pinching the lug, you might want to crimp with a larger die first then crimp again with a smaller die. You can also get hydraulic crimpers which seem to get good reviews.

hydraulic crimpers
An acceptable crimp

Make sure to pull really hard on your lug after crimping it. Any movement at all is unacceptable, the lug should be permanently bonded with the wire. Use heat shrink to cover the crimped part of the lug and you’re done.


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Switches and Switch Panels

Switches come in many different forms, but we’ll keep it pretty basic and just talk about your average on/off switch. They will be rated for either DC or AC applications, make sure that you’re using DC rated switches for your DC circuits and not a typical wall switch you’d find in a house. This is important because DC current is harder to interrupt then AC current so the internal contacts of a DC switch will be physically farther apart when the switch is off to prevent the current from jumping the air gap.

All switches will also have a maximum amperage rating which is obviously the maximum amount of amps the switch can handle safely. Just make sure the switches installed on your circuits have a maximum amp rating above that of the appliances in that circuit.


My Two Cents

Electrical is a pain even if you know what you’re doing. My advice is to design your system on paper many times before committing to purchasing anything. Double and triple check your math that determines the wire gauge choices for each circuit. Also make sure you have the right tools for the job, it will remove some of the frustration. Consult online forums and contact manufacturers when you’re unsure about anything and keep notes. Here is an example of our wiring diagram that will help you get off on the right foot when designing your electrical system.

Hope this guide gave you some value and cleared up the confusing world of electrical. You can find links to all the equipment we used in our van build at our van build shop.

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