Early consideration should be given to how you plan to add electrical wiring to your bus conversion. The first decision is whether you’d like to embed your wiring in the insulation and cover up your electrical wires with your wall and ceiling panels, or if you’d like to run your wiring exposed, in a conduit chase, underneath your bus, or a combination of all of those options. 

While I was anxious about burying my wiring in spray foam insulation this is what we ended up doing with much of our electrical wires. You may decide on the other hand that you need access to your wiring indefinitely to make modifications or repairs and you could plan to have it all exposed or in an accessible chase. If you plan your wiring correctly and well ahead of insulating or covering the walls and ceiling you can do so with confidence knowing that as long as you don’t nail or screw into a wire and have sized your wires accordingly, they are safe and protected behind your finished walls. If however you can’t seem to decide on the locations and power requirements of every outlet, light and appliance ahead of time know that it is absolutely okay to create exposed wiring (preferably in the proper conduit) and you can usually find ways to hide it.  

Regardless of how you run your wires an early and important task is to determine your power needs. You need to establish what electrical appliances you will use, what their power requirements are, and their specific locations. For example an AC refrigerator generally requires it’s own 15 amp circuit, while an electric water heater will need wiring that can handle 20 amps. Luckily for AC circuits there are two common wire sizes that will accommodate all of your power needs. For 15 amp circuits you will use 14/3 (the 14 refers to the gauge or thickness of the wire and the 3 refers to how many electrical wires or conductors are in the wire) and for 20 amp circuits you will use 12/3 which is a thicker wire that will allow more current through it without overheating (and potentially causing a fire). You could in fact decide to use the lazy but more expensive method in wiring your AC outlets and appliances and just use 20 watt circuits with 12/3 wires. I would plan out your AC appliances, circuits, and wiring first, because as you will soon see it is much easier than DC wiring. 

Now having said that DC appliances, lights, and fixtures are generally more efficient than their AC counterparts (when available) especially because they don’t require inverting to AC power which requires additional energy. If you are building a Skoolie that you are maximizing for off-grid energy consumption you should use as much DC power as possible. That means your lighting will most certainly be DC, your exhaust fans will be DC powered, many of your outlets for phone chargers and camera chargers could be DC, and your refrigerator could use DC power as well. The tradeoff is that some of these appliances are more expensive than their AC counterparts and with less options available. If by chance you are building a conversion that will always be plugged in to shore power, then going all AC is absolutely fine as you will always have ample power and no need for a DC system. 

Now with DC fixtures and appliances it is also important that you dial in the specific products you will be installing and find out how many amps they use to determine correct wire sizes. However because power consumption of DC appliances can vary so much it is not quite as simple as choosing wiring for 15 amp and 20 amp circuits as with AC power. The absolute easiest way I’ve found to determine wire size is the following online tool: http://circuitwizard.bluesea.com/ where you will plug in your voltage (which is 12 Volts), the amps that your appliance uses, and the roundtrip wire length to get power from your DC distribution block to your appliance (if your appliance is 20 feet away from your DC distribution then plug in 40 ft). You will quickly find that many DC appliances will require rather large wires even though their power consumption is low, but for almost all of your appliances you will likely end up choosing 12/2 for the more power hungry, and 14/2 for everything else (DC cables have two wires instead of 3). 

Now that you’ve planned out your electrical system and purchased your wires it’s time to start wiring! If you are doing the majority of your wiring before insulating like I did then you’re going to want to start your wiring runs where they will enter your AC electrical panel and your DC fuse blocks. Ideally these will be in the same location and at a centralized location on your bus to reduce wire lengths. This could be in a dedicated closet, or underneath a couch or a bed. Consider that this is likely also where you will house your battery bank, charge controller, inverter etc. so be sure to plan for enough space. Some Skoolie converters choose to have their distribution centers in the living area so that they can access them if breakers trip or fuses break, but choose to house their battery bank and inverter in the undercarriage storage (which may then potentially need to be heated or cooled to maintain temperatures). In our bus we chose to create an entire electrical closet in the center of our bus just after the kitchen to house all electrical components. Once you’ve left ample wire to make connections at that location you can pull your wires to their destination and secure them to the ceilings and walls. To do this we chose to use duct tape, but it was not sufficient when spray foaming to keep wires entirely in place. A better choice would be to use adhesive pads with zip ties attached such as these. Be sure to leave enough wire at the destination for a bit of flexibility when installing your appliance. 

Now that you’ve figured out what size wires and how much to buy it’s time to decide what wires to use as there are a few options. Option number one is regular residential wire generally made by a company called Romex. This wire comes sheathed, is generally yellow, and is made up of solid, rigid copper. This is the cheapest option, however it is not the best for many scenarios. While the validity of this argument has been debated at length, the premise is that vibrations in a vehicle over thousands of miles could actually snap a copper connection in half. If that were to happen the result could be challenging to fix, potentially dangerous, or really of not much consequence. Who really knows. If you don’t plan to drive much and are on a budget I think this might be the right wire choice for you. However this solution is just for your AC wiring. DC fixtures are generally set up to connect to stranded wire with crimp connectors which you will learn about below.

Option number 2 is stranded copper wire which is exactly what is found in automobiles for the reason that I mentioned above. This copper conductor is made up of hundreds of tiny strands of copper which are much more flexible and will not break from vibrations. This is a great solution for both AC and DC wiring. The only issue with this wire is since it’s made for cars which run off of DC power I haven’t been able to find stranded copper wire which is sheathed and bundled together with 3 wires for AC power or 2 wires for DC power. This is absolutely not a deal breaker. All you need is the right conductor to do the job, but as a result you will have to run your two or three wires seperately which makes wire management just a little bit more difficult and the job just a little bit more complicated, but don’t let this stop you from buying automotive wire especially if the price is right and you feel it makes sense for your application. 

The third option is the grandaddy of wires, the tinned copper marine grade wire. This product is top notch, and the least likely to fail in any scenario you could throw at it in a bus conversion. The reason for this is that it is created for humid, salty, and corrosive marine environments. Copper will in fact oxidize eventually in humid environments which means that your electrical connections are at risk of failing someday from corrosion. Will it fail within the time you are using your bus, however? Probably not. If it does fail it is not like your wiring is ruined, but you may have to do some work to reinvigorate electrical connections. If you want to ensure that you won’t have to deal with that labor or risk then the tinning process done to marine wiring delays this failure probably for decades which is why it is used in sailboats. If you are doing a professional school bus conversion I would consider using this wire. If you have the budget for it and want the best I would also consider using it, and this was my reasoning for using it in my bus conversion. It also conveniently comes in sheathed and bundled cabling for ease of use.

While wiring for DC lights and outlets and AC outlets that will be in exposed boxes can be simply left dangling in their appropriate locations, now is the time to install boxes for any outlets that you plan to have inset in your walls and for AC light fixtures at their destination. This will make for a great finished product in any exposed areas in your bus and is required for safety reasons as well (all AC connections must be made inside a box). You can use plastic or metal boxes and screw them straight to your bus walls at the appropriate depth (you may need to install wood blocks behind them) or if your furring strips are thick you can screw them directly to your furring strips. Be sure when installing them to set them to a depth that will allow them to be flush with your finished walls. If your finished walls are ½” deep than the box should extrude ½” from your furring strips for example. In installing your outlet boxes you should also give consideration to your wire management. The wires in your walls may be moving up and down as your bus drives down the road and the sharp edges of the boxes where the wires enter may cause a short or even a fire if wires break. Your wires therefore need to enter the boxes in a safe and secure way such as with Romex wire clamps like these. You can also use outlet boxes for wire management if you need your wires to exit a location such as in a wall but you need them to continue into say a couch. You could have your wires come through a hole in the plywood, but an outlet box with wire clamps would be foolproof long term. 

Now when you are making your final electrical connections to your outlets, lights, DC fixtures, and fuse blocks for standard solid copper cabling you can proceed as you would in residential electrical work which means you can strip, bend, and tighten your cable around screws on the outlets and lights. However for stranded wires this is not an acceptable solution. For stranded wiring you should use crimp connectors which you can buy in a large pack with a variety of gauges and connector types. This will allow your stranded wires to take on different shapes for the final connections. To do this you can use either automotive or marine grade crimp connectors. Either are fine, however one is a little easier and the other is a little more waterproof. For the automotive crimp connectors you will strip back the appropriate amount of insulation on the wire for the connector, twist the wires, push them into the connector, and then crimp them with the appropriate sized crimpers. These crimpers will allow you to crimp several wire types securely and are great for ensuring secure connections  For marine connectors you will do the same, however you have the option of using a heat gun to soften and secure the built-in heat shrink around the connector and the cable ensuring that no water will ever enter that connection. From there you will securely tighten your connector to your outlet or fixture using the provided screw with the correct wire, secure the fixture, and you’re done! You will do this for all of your AC and DC fixtures using the appropriate connector for the application. 

Now if all of that sounds awfully intimidating then consider that you don’t have to be a hero and do it yourself. You can go and hire an electrician to do it for you, but go equipped with your research having read this article maybe a couple of times because there is no guarantee that your electrician will know the ins and outs of wiring both residential, and low voltage, and RV/mobile applications and you MUST check on his/her work and I’d say it’s still your responsibility to know what size wires go to what fixture at the very least, because this is an important decision that all parties must agree on. Having said that I would encourage many of you to have a hand at doing your own wiring. Start simply by doing your research and coming up with a solid plan, continue with the rough-in wiring which can be as simple as zip-tying, and taping wires to the ceiling and walls of your bus. By the time you’ve done both of those, and are equipped with the right tools you will find that making electrical connections is within the scope of capability of almost all of you, and you will not only save money by doing so, learn a new and useful skill, but you will now have most of the troubleshooting skills to know when something has gone wrong and how to fix it, and you won’t have to call for expensive help if/when it does.