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Wire Type and Fuel Tank Sealant

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  • Wire Type and Fuel Tank Sealant

    I’m almost ready to close up the left wing. I have a heated pitot tube (Dynon), fuel transfer pump and WAT Blaze position/Nav/Strobe lights, and Flyleds Taildragger Pulse landing/taxi lights. The install directions suggest wire and AC 43 has a section to determine gauge based on power and length. I can figure that out I’m just unsure if I need shielded or unshielded. Thoughts?

    Pitot Tube 14v 10 amp CB, approx 20’
    Facet Fuel Transfer, 14v 3-5 amp CB approx 25’
    WAT Blaze, 14v, .4 amps (2.15 amps for the strobe) approx 30’
    Taildrgger Pluse, 14v 10 amp CB approx 35’ - calls for unshielded for the landing lights but doesn’t say unshielded or shielded for the taxi light.

    There is unlikely to be any avionics in the left wing.

    Has anyone put any type of sealant where the filler neck exits the upper skin of the wing? If so what did you use?

    Thanks,

    Nick​
    N750HT - Model 5
    KCNI
    https://eaabuilderslog.org/?blproject&proj=8Fr0X26jS

  • #2
    I would not use shielded wire for any of those. If you are using Dynon, I would also make provisions for a wing-mounted magnetic sensor. Mounting out in the wing can make some distance from the steel fuselage structure. It requires a SV-Network cable. Just as a quick check, if you are using a 5A fuse, you'll probably find something around 22g wire appropriate, or a 7.5A fuse for 20 gauge. The pitot heat will have a bigger wire, possibly as much as 10 gauge but I can't remember for sure. The pitot box probably also has some smaller wires coming off too, in addition to the heating element?

    I use gray RTV sealant from the auto parts store for the fuel filler neck. I absolutely seal that gap, because if the fuel tank vents and it is not sealed, fuel will run down between the top of the tank and the wing skin, and thence into the wing structure. Fuel dripping off the back of the flap is sub-optimal, but fuel collecting inside the wing structure is dire. I would not apply this sealant until your wings are painted. Maybe around the same time you apply the required capacity and fuel type placards.

    Comment


    • #3
      Thanks Jared. You were right 10 gauge for the pitot heat.
      N750HT - Model 5
      KCNI
      https://eaabuilderslog.org/?blproject&proj=8Fr0X26jS

      Comment


      • #4
        Jared is correct that there is no need for shielded wire for the circuits you describe. I'll add a bit of explanation for anyone interested. Shielded wire is used for cables that carry some form of signal (audio, data etc.) and is intended to reduce the likelihood that outside electromagnetic interference will add noise to the signal. The need for shielding depends on how electrically noisy the environment is and the level of sensitivity of the signal/receiving device. Aircraft power wires are carry 12 or 24V direct current - no AC signal component means no need for a shield.

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        • Steve W
          Steve W commented
          Editing a comment
          Even the DC wiring for the facet pumps in the same wing as the GMU 22?

        • gregc
          gregc commented
          Editing a comment
          Flowing DC current does create a magnetic field around the wire. Routing power wires away from a magnetometer is a good idea. However, I'm pretty sure that wire shielding only effects EM fields and has no effect on magnetic fields so shielded wire would not help anyway. To reduce/eliminate the magnetic field you would need some sort of counter current. In practice, as long as you don't have a big loop of extra wire right next to the GMU22, it should be fine.

      • #5
        As Greg mentioned shielding the GMU wiring is needed but not the power and grounds to components such as the fuel pump.

        Grounds are notorious offenders in wiring any vehicle, and running home-run grounds is the best preventative method to ensure good signal quality long term.
        Using airframes as ground connections opens oneself up to issues over time.

        Run all grounds to a bus bar or ground connection direct tied to the battery, or at least closer to the battery than any signal generator.

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