Installing wires in conduits

Hi Everyone,

Like a lot of people, I installed conduits in the wings prior to closing them up and now I'm at the point where I need to install the lights and such. My question is specifically whether or not I need to secure the wires in those conduits somehow? It seems odd to me that a wire bundle needs to be secured at a minimum of every 24 inches (AC43.13 11-146) but that wires in a conduit almost 10 feet long can just flop around.

Could someone offer some insight here? Have I missed something obvious?

Thanks,
-Ross

Only conjecture here, but I believe the idea of a conduit is that a) it makes it easy to pull wires in the future, and b) it prevents them from flopping around, so no need to secure like conventional wiring. I would secure the wire at both ends of the conduit.

Brian

Just me

I am using conduit in the wings because the wings were skinned long before I had decided on all the wiring; and I didnt want to hold off skinning till the end. For the fuselage, I am not doing conduit but rather tying the wires together using lacing tape. I dont worry about the wires flopping around inside the conduit. It seems impractical to tie the wires together inside a conduit. Also, I dont see much need to re wire the wings in the future, but I do see the fuse wiring forever being changed.

Northernliving said:

Only conjecture here, but I believe the idea of a conduit is that a) it makes it easy to pull wires in the future, and b) it prevents them from flopping around, so no need to secure like conventional wiring. I would secure the wire at both ends of the conduit.

Brian

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What Brian said! In addition, run an extra pull string and tie at both ends for future use. But if you forget, a cotton ball tied to a string and a vacuum on the other end will do the trick.

Conduut

10builder said:

What Brian said! In addition, run an extra pull string and tie at both ends for future use. But if you forget, a cotton ball tied to a string and a vacuum on the other end will do the trick.

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Wise words. After a career in Telecom ("wirejock"), I never pull a wire in without an option for the next.
Our General Contractor and Electrical Contractor thought I was nuts. Blue conduit was required all over the house. Almost every one has a wire in it now. Every one with a wire, has a pull string for future use.

AC43.13-1B has some relevant requirements in Section 8 - Wiring Installation. They include:

11.96.a. Wires and cables are supported by suitable clamps, grommets, or other devices at intervals of not more than 24 inches, except when contained in troughs, ducts, or conduits.

11.96.m. Ensure that wires and cables are not tied or fastened together in conduit or insulating tubing.

11.115 Protective flexible conduits should be made of a material and design that eliminates the potential of chafing between their internal wiring and the conduit internal walls.

There's quite a bit more there, but basically the FAA is saying that conduits provide mechanical protection to wires, and their interiors won't themselves damage loose wires. Our aircraft don't need to meet these requirements, but they are based on lots of previous experience and are a good guide unless we have a specific reason for not following them.

It?s an experimental aircraft! Just throw the wires in there and let us know if you get sparks eventually. I?d rather learn from others mistakes than my own.

Seriously though, I put the wires in the conduit without tying them. I secured the bundles on each end of the conduit with plastic wire ties for more of a strain relief than anything. I didn?t put pull strings in the conduits until I was ready to run the wire. Tied a couple of cotton balls on the end of a string and sucked them thru the conduit with a Shop Vac. Worked like a charm! Not necessarily the right way of doing things but it worked for me. I?ve got about 300 trouble free hours so far.

dmn056 said:

AC43.13-1B has some relevant requirements in Section 8 - Wiring Installation. They include:

11.96.a. Wires and cables are supported by suitable clamps, grommets, or other devices at intervals of not more than 24 inches, except when contained in troughs, ducts, or conduits.

11.96.m. Ensure that wires and cables are not tied or fastened together in conduit or insulating tubing.

11.115 Protective flexible conduits should be made of a material and design that eliminates the potential of chafing between their internal wiring and the conduit internal walls.

There's quite a bit more there, but basically the FAA is saying that conduits provide mechanical protection to wires, and their interiors won't themselves damage loose wires. Our aircraft don't need to meet these requirements, but they are based on lots of previous experience and are a good guide unless we have a specific reason for not following them.

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Thanks Dan. I've just installed conduit in one of my wings today, and was going to start pulling wires through later. I had thought of using tape to secure similar bundles - e.g. the wires for pitot heat together, but now I won't bother. I'll just pull them through and secure them where needed, either at the pitot or in the tip for the lights.

BTW I used a tiny coated wire (I think it's the kind of stuff for used for making spinners on the end of fishing line) as my draw-string. It was strong enough that I could just push it through from one end, I just doubled over & taped the end being pushed through so it didn't snag on the way.

I didn’t leave the string in the conduits after completion. I was concerned about moisture collecting in the fibers and couldn’t think of a way to secure the string so it would never come undone and foul the control linkages.

No string necessary gents, ever used a fish tape? They work quite well.

unless...

when trying to push the fish through the conduit it get tangles with the already installed wires...

I used a fish taped on some of my conduits and this happened several times. The end of the tape was curled over and some of the smaller wires ended up getting caught it the end of the tape. I ended up cutting off and rounding the end; helped a lot.

I also used the string method, using Spider Wire fishing line...very small with a very high break strength.

rgmiller1974 said:

I installed conduits in the wings prior to closing them up and now I'm at the point where I need to install the lights and such. My question is specifically whether or not I need to secure the wires in those conduits somehow? It seems odd to me that a wire bundle needs to be secured at a minimum of every 24 inches (AC43.13 11-146) but that wires in a conduit almost 10 feet long can just flop around. Could someone offer some insight here? Have I missed something obvious? Thanks, -Ross

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I don't think we are answering the OP's question. Ross that is a good question. My opinion and short answer is no need to secure the wires running thought the wing conduit. (opinion as follows)

Assuming the conduit is light, thin walled, poly/pvc tube secured to ribs with a 1" or 1.5" diameter, it should provide a safe place for the wires to live without damage to their insulation. Of course use only aircraft quality ETFE insulated silver coated wires. Don't use cheap vinyl insulated copper wire from auto parts store. All the wires I assume are for lights, positive polarity, all fuse/CB protected running the same way. The "worry" I suppose is rubbing, chaffing, shorting? That's pretty unlikely. I assume the wire gauge is 18 awg or 20 awg the wire pretty much just sit there, not move much. Also wire bundles laced together can have wire chaffing especially in high vibration areas. I don't consider wing a high vibration area. Having the wires in a loose bundle in the tube has the Pro of running cooler than a tight bundle...

You do have the option to feed all the wires at the same time and lace them together.... however removing a wire will require you pull all the wires out.