Wire For EAB Aircraft

[az_gila]

While I fully agree with the comments above...

From a reliability point of view I would be more concerned by the use of cheap Autozone/Walmart type crimp connectors, which I see frequently on RVs...

[RFSchaller]

Gents,

The point I was trying to make is that for most of our applications the environment and amp loads at not unique to aircraft, and automotive applications are equivalent. Yeah, I wouldn't use TV coax to connect my Nav antenna, but I see nothing wrong with automotive wire for avionics power.

The resale value may be a valid point, but RV owners are spoiled! Many (not even "most") home builts on the maret are completely inferior to RV with regard to quality of parts and use a lot of parts and fasteners that would never meet AN or MILSPEC standards. That sounds like a condemnation, but it's more of an observation that non-aeronautical parts are frequently used in home builts, so unless the wiring is substandard I doubt most buyers would consider it a big deal.

Have a Happy Thansgiving!

Rich

[lrgabriel]

Crappy wiring materials and practices are a huge problem in the experimental world. A lot of lessons learned and lives lost went into developing the current standards for aircraft wiring, and for the sake of saving a few cents, I'm not willing to relearn those lessons. Neither should you.

The point of experimental aviation is to expand the boundaries of aerospace knowledge. We should be taking certified practices and principles and improving upon them--not seeing where we can legally cut corners and reduce cost. If you have an idea for a better type of wire than what the current mil spec specifies, then by all means experiment with it! The community learns nothing, however, by experimenting with crappy wire that we already know is crappy.

The FAA has been on big electrical kick in recent years, with good reason. Here's an interesting read if you'd like to know more.

The operating environment (not to mention consequences) are completely different between the aerospace and automotive industries. There are SEVERAL reasons aircraft wire exists; otherwise we'd all be using the same kind of wire. Even if those reasons aren't important to you, the service life, maintainability, and ease of installation of aircraft wiring should point you in the right direction. Try working with mil spec machined pins, a Daniels crimper, and aircraft wire for a week...then give stamped pins and auto wiring a shot.

[RVDan]

I' m with Gil. Those cheap crimps are a real problem. No strain relief.

[RFSchaller]

Oddly enough the only electrical fire I ever had was in the certified wire harness of my transponder installed by an avionics tech in my Cherokee. Anything can fail. Just because it isn't MILSPEC doesn't mean it's "crappy". EXPERIMENTAL means we get to make the decision. We all have our self imposed limits. I don't criticize those with limits different from mine. I try to see if there is something I can learn from them. In the end the decisions are personal.

[lrgabriel]

Being part of experimental aviation means on some level deciding you can do better than the current standard, which by nature means the standards have room to be improved upon. There have obviously been failures of the best parts we've produced or certified to date. I'm not claiming the specifications are infallible.

What is paramount and universal, though, is understanding the requirements of your situation and how your solution meets them. If you're not going to take the accepted/standard path, then you really need to do the hard math and research behind your course of action before putting butts on the line.

There's a lot of data available to help you decide what gauge wire, what construction and metallurgy, and what insulation properties (heat dissipation, electrical properties, chemical resistance, resistance to chafing, etc) are needed to survive in an aviation environment.

It's entirely possible a niche industry other than aviation makes really good wire that will handle all the shenanigans we throw at it, and do so over the 20 (30? 50?) year life of an airframe.

But...aircraft wire is already built to meet those requirements, incorporating the best knowledge in aerospace.

Choosing another path is entirely up to the experimenter, but it should always be approached with the amount of thought and engineering appropriate for the level of risk/importance. Substandard components and poor wiring practices have caused an engine failure, a cabin fire, and a complete flight instrumentation failure in three E-AB airplanes that I've seen in my short time exposed to the homebuilt world--electrical systems are important, and my vote is to use stuff that we know works well.

[wilddog]

Tefzel wire and mil spec connectors are so much nicer to work with than auto stuff there is no way I would try to save a few dollars there. It is lighter too.

[Walt]

Originally Posted by lrgabriel

Choosing another path is entirely up to the experimenter, but it should always be approached with the amount of thought and engineering appropriate for the level of risk/importance. Substandard components and poor wiring practices have caused an engine failure, a cabin fire, and a complete flight instrumentation failure in three E-AB airplanes that I've seen in my short time exposed to the homebuilt world--electrical systems are important, and my vote is to use stuff that we know works well.

Agree totally. On more than one occasion (many), I've had to repair problems associated with inferior components, wiring and workmanship. The electrical system is a critical element in todays aircraft, give it the respect it deserves.

[epaslick]

Originally Posted by lrgabriel

The point of experimental aviation is to expand the boundaries of aerospace knowledge.

With all due respect, the point of experimental aviation (particularly the homebuilt world) for the vast majority of participants is to be able to partake in a hobby and/or lifestyle that would otherwise be financially out of reach for them. Even in the homebuilt world, aviation is a very expensive pastime. I don't begrudge anyone trying to cut costs as long as they are doing so SAFELY.

So the question is can automotive wire be used safely? I think that depends upon what you are doing with it, although I wouldn't use it because of the weight.

[RVDan]

Originally Posted by epaslick

So the question is can automotive wire be used safely? I think that depends upon what you are doing with it, although I wouldn't use it because of the weight.

I think the answer to the "safely" aspect is how well one understands the limitations of "commercial" wire, automotive or not. While there are commercial wires with similar performance characteristics to AS22759 wire, they end up costing about the same. We are talking about "cheap" wire, so typically PVC or some variant of insulation.

For example if you use wire with 85?C insulation in environments hotter than that, i.e., firewall forward, you can be pretty sure you have compromised the wiring. If the wire is required for continued safe flight and landing, safety for sure. The 85?C rating is not just the environment but the self heating of the wire due to current flow added to the environmental temp. This is why the minimum for aircraft wire is 150?C. The curves published for wire loading in AC43-13-1B are all based on 150?C wire in a 20?C environment. So if you use a lower temp rated insulation you have to derate the wire current carrying capacity and use smaller fuses or CB's for a given wire size. I have conducted actual wiring current carrying capacity testing for aircraft. Temperature is the limiting factor and is the limit is driven by the insulation's ability to withstand the elevated temperatures.

Then look at abnormal conditions- a wire overloaded due to a malfunctioning device or ground faulted in an arcing situation which doesn't blow the fuse or open the CB. Assuming that the wire is not Tefzel or similar material since you are trying to save money, the wire overheats and the insulation first produces copious amounts of noxious smoke, then it catches fire and burns really well. Since the fire is somewhere under the instrument panel or under your seat, you have no idea what fuse to pull to stop it. If the wire is in a bundle now the rest of the bundle is compromised and catches fire.

You are probably saying that this won't happen because you have fuses. But you used the fuses suggested by AC43-13-1B and so your wire is only protected from reaching 150?C. Your PVC wire is melted by then.

If you are IFR this is a serious situation likely to kill you, VFR is no fun either.
I know about a glider that crashed due to an electrical fire and smoke in the cockpit. Cheap commercial wire was used.

Would you say this affects safety?

AS22759/16 or /34 wire will produce limited smoke and will not sustain fire even if overheated severely.

A note on "teflon" wire. Pure TFE insulated wire is bad for general aircraft wiring applications. It resist high temps really well, barely effected by a burner flame, however pure TFE will cold flow when pressure is applied. Simply tying or clamping the wire bundles can cause pure TFE insulation to thin out at the pressure point eventually becoming so thin the insulating value is compromised. I did testing on that also.

Happy Thanksgiving to all.