Aircraft Electrical Wiring
Review AC 43.13-1 for wiring selection and load ratings. Based on the electrical component and the amperage draw of the component and the known length of the wire run you can determine the appropriate wire size for the installation of the component. The part manufacturer may also have installation instructions and provide you with the required wire size for the installation. If no wire size is given then you will need to use the charts in AC 43.13-1. While we are all in the bookwork at the moment this would be a good time to start a shopping list of electrical items you will need that are not a part of the basic kit.
Now take a look at a basic electrical system such as position lights. All power first starts from the battery. The battery has a + or power side and a - or negative side. The negative goes to ground (the aircrafts metallic structure) and the positive "sends out" power. When we install our cool position lights we are placing them between the + and -. The lights are mounted in their appropriate locations and the instructions will show that we need a ground. This ground can be connected directly at the mount location if the structure is a conductive metal. Keeping runs of wire as short as possible reduces additional wire weight. The common ground for the aircraft is the aircraft structure itself. With our lights in position and a ground installed we have completed one half of the electrical sytem for our lights. We need to get power to the lights. We need a means to control the lights and we need a means to electrically protect the circuit from shorting out and starting a fire. After looking at the installation print we see that the lights draw a maximum of 5 amps so we get a five amp switch and resettable circuit breaker also of this rating of 5 amps and the appropriate gauge wire. We have already checked our aircraft electrical system rating and selected a terminal strip that will meet our requirements. The terminal strip is located near the instrument panel but out of the way from getting damaged. The proper size wire is run from the battery to the terminal strip. The terminal strip is now our little 12 volt power supply that we can tap off of for all our other systems as well as our position lights. We mount the circuit breaker and switch. Now select the proper size wire and run from the terminal strip to one side of the circuit breaker then run a wire from the other side of the circuit breaker to one side of the switch. From the other side of the switch we run a wire to our position lights. We now have completed the power side of the circuit and completed the position light installation. Go ahead turn them on and see if they work.
The hypothetical system we just created was to give you an idea of what can be expected when planning and installing electrical wiring and components. It's hoped your electrical juices are now flowing and you are thinking of all the different types and sizes of wires that you will need. With each system you choose to protect you will need appropriately rated circuit breakers and switches. Why not break this down a bit for you?
You will need some type of terminal bus to split the batery power off to the different electrical systems. There are a few different ways this can be done and are shown in AC 43.13-1. Pick a set up that best fits your kit and accessories installation. Your usual options are terminal blocks, terminal strips, or a bus bar.
You will also need ground points to finish off the circuit. On most small kits a single point may be sufficient or you may need more with a larger kit or gyroplane with more options installed. In any case you will need some common hardware for use as the ground points.
I am sure you are saying, "I had know idea I would need all this". Now to be fair to the kit manufacturer- they have no idea of what you plan to install and how you will install your electrical system. I will also be very honest with you and say that electrical installations can be very tedious but they are not difficult either.
It should also be mentioned that wiring that should be used for your communication should be a different type of wire than used in most other applications. Wire used in communications should be shielded wire, which is more expensive and has some unique installation requirements to be effective. The purpose of shielded wire is to provide a ground for any stray signals or voltage can find instead of getting into your comms. and headset. This stray RF can cause static or even make communication impossible if not properly compensated for.
Another form of wire that is also shielded is coaxial wire and is used to connect your radios to their antennas. Some inexpensive tools can be purchased at the local Radio Shack to prepare your coaxial wires. I know your head is ready to explode from information saturation so get up, grab a cup of coffee or tea and use the little room and then get going again because wiring gets easier from here.
When installing electrical wiring and ground points be sure to do a continuity chaeck to make sure you have good contacts as you progress with the installation. A bad ground point can cause some real headaches if you have to troubleshoot when the kit is fully assembled.
On that note let's consider something. It has been my personal experience that corrosion causes more electrical system failures then just about anything else. This corrosion is usually found at the contacts or terminals. If you live near salt water your corrosion issues are going to be magnified. I suggest using an anti-corrosion film to protect these areas. Spray protectants such as Corrosion X or ACF-50 and the like will help prevent the formation of corrosion. It really is cheap insurance to keep your electrical system in shape. Be aware that you do not want these types of products on natural rubber compounds like hoses because the product can breakdown the rubber. Silicone rubber dust and moisture boots can be installed over studs and are highly recommended in areas exposed to the elements, such as starters and alternators.
Installation of bonding straps will also help in two ways. Bonding straps are small wire straps that electrically bond large components to each other. This helps even out the electrical potential throughout the airframe. In laymans terms this will help ensure your electrical items will operate without interference noise and reduces the effects of corrosion. The engine and any electrical motors should be bonded as a minimum. Imagine a two hour flight with an electrical fuel pump whining in your headset or helmet.
It is highly recommended to purchase an aviation grade terminal crimper. I know they are expensive but you can be certain the crimp is good and will not fail prematurely. The wire behind the crimp may fail but rarely will the crimp fail. This tool is so simple to use and will save you a lot of future problems.
To further help you get that wire laid in we will next look at terminal connectors. But take as much time as needed to make sure you have all the wire you will need, jot it down on your shopping list then move on to Terminal Connectors.
East Coast Aircraft Supply (ECAS)
Parts Logistics - Aviation Wire