Wire size to my heated pitot tube

Hello all:

Well I have read all there is to read and searched all the forums to only be more confused! Sorta goes with this RV building thing don't ya think?

Anyway I have a 12V heated pitot on my left wing as it gets pretty cold up here in Canada and thought I might need it.

The distance from my centrally located terminal block to the pitot is 8.5 feet and when connected to my multimeter it draws 4.81 amps and gets real hot.

Question:Marc Ausman in Aircraft Wiring Guide recommends a 14 gauge wire for 15amp draw, I intend to use 14gauge wire for this run... would you agree?

Also many say I should twist the wires (both ground and hot) all the way to the pitot to avoid noise..... why not use shielded cable?

Any and all comments greatly appreciated..
Dave

I doubt you'll find shielded 14AWG.

Because your pitot heater is purely a resistive device and not vulnerable to small bits of AC interference, I see no need to twist the wires either.

Since you have a total run length of 17 feet (8.5 from the block to the pitot, and another 8.5 back to ground means total circuit length is 17ft), AC 43.13 recommends 14AWG for anything up to about 10A. Since your pitot draws less than that you'll be just fine.

14g is a good choice. I would twist them to help cancel magnetic fields, especially if you are running near a magnetometer.

As mentioned above, I don't thing you will find that gauge shielded but you are not twisting the wires to avoid noise the way you do for LED lights.

what does your pitot tube manual say to use?

I just went through this exercise adding a heated pitot. Mine actually draws 10 amps, but the calculations for the length of my circuit indicate 14 gauge as well. I get no noise from the pitot wires, but I have noticed that the harder my alternator works the louder background whine is that I get from it.

Thanks a bunch!

Atta boy AX-O.... if I had the manual would I need to ask the question?hmmmm lemme see. In true homeuilding spirit I sourced the pitot in an auction of aircraft parts... alas no manual.

Thanks for the responses it makes one feel better when others review and agree on the game plan, something I treasure VAF for.

The reason I asked was because I bought A Dynon heated tube and missed the fact it called for a specific size wire. So, I did the calculations based on the amps used by the tube and transferred that to the wire chart. I then ran the wire in the wing. A few days later I saw that the instructions called specifically for a wire size. So I had to re do the work.

I was not trying to be an a$$. Just trying to save you from the same mistake I made. You did not state that you bought a used pitot and did not have the instructions.

5A / 60W is a pretty weak heater for a pitot. Plus you need to test at 14.4V, not 12V since these are generally restive. Most are 100W, which is at least 7A. You need to make sure it's not a temperature regulating pitot, because it might draw more current in 200MPH -20C air than at room temp and you need wire size to support that.

Once you know the current and length, AC 43.13 gets you what you need.

--Ian @ Dynon

Good points. When you need it most, it will be sucking a lot of power to melt the ice.

My suggestion was based on 43.13 and the Dynon heated pitot tube installation for an RV-8 and -7A where 14g was suitable.

Thanks again all.

No prob Ax-O and Dynon that is great I should have thought of the volts x amps = watts thing.

So much easier to just buy NEW, maybe I will just get the new AOA Dynon that will send to my Dynon Skyview.

Sadly this project is soooo far from affordable

Thanks all