Ola' everyone.

What is the rule for using shielded vs. unshielded wire?  I understand the EMI and the reasoning behind shielded, but why are some wires in our aircraft unshielded?  To prevent interference, shouldn't ALL wires be shielded?

Example:  Shielded for the strobe/nav lights.  What about landing and taxi lights?  What about flaperon motor?  My Dynon autopilot wires are not shielded.  Why not?

Thanks guys.

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Hi. You could shield every wire, but it is only important for the wires that emit a lot if interference or for the instruments that are sensitive to it.

The power supply of a radio is usually not shielded, there is a voltage regulator that would filter EMI. The wires that gets the comm from the radio to the headset are low power and com signal is sensitive to EMI, you would ear it. These should be shielded.

Landing light is constant, resistive load. This does not cause a problem. Strobe are made to emit pulses of light, so they generate EMI.

Regards,

Francois

Thanks for the reply. 

To quote you: "You could shield every wire, but it is only important for the wires that emit a lot if interference or for the instruments that are sensitive to it."

My question is:  How do you know what wires emit a lot of interference or which instruments are sensitive?  Is there some formula or something?  It's probably obvious, but I don't get it.

Allan,

For EMI think high voltage or large magnetic field. Your first thoughts are probably “In a Zenith? Is he dreaming?” The answer is yes. Aero LEDs call for shielded wire due to high pulse voltage that might impact your comm or other instruments that are rarely found on a Zenith. Their website (somewhere, I read it there) explains why they call for and sell shielded wire for their lights. Not much else on Zenith has high voltage or calls for shielded wire. As a precaution avoid routing your ELT (antenna) or comm wires along side your LED shielded wire. Not much else to worry about. Low amp, 12 volt wires just don’t emit much EMI and that is what most of your wiring is.

If you install a electric artificial horizon instrument it may mess with a nearby compass. Everything seems to mess with compasses.

Ralph

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