Shielded cable for power?

Nathan Miller

Nathan Miller

Pre-takeoff checklist
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Nathan
I goofed. I assumed / rushed when I was putting together my order with 'spruce and ordered 2 conductor shielded cable to power my GMU 11 Magnetometer in the wingtip instead of separate unshielded conductors they spell out in the install manual.

So, here is my muddied thinking and I would appreciate advice, please:

-"Back in the day" - it seems conventional wisdom was to run power and ground to the airframe to complete the circuit. I'm tempted... but
-Today, best practices seem to indicate that it's better to run a separate "lo" conductor and ground everything to a single ground bus.

So, -run the shielded 2 conductor because I have it?
or -save the $25 differential and go with a single conductor and ground to the airframe?
-Any problems using a shielded cable when the install manual doesn't call for it?

Thanks for patience with the newb questions,
Nathan
C172N
 
There should be no problem running a shielded pair for power and ground, as long as it is the appropriate gauge and is separate from the CAN Bus. I did a quick search in the install manual and didn’t see anything that said the ground must be run back to the same point, which means it could be grounded locally. However, he manual may say that, I just didn’t find it.
 
If the manual says 2 unshielded wires, do not use aircraft structure for ground conductor. The pair must be isolated to keep out other voltage differences.

Putting the pair in a shielded cable is perfectly OK, as they remain un connected to the air frame. The shield should only be grounded at the instrument end, to keep ground currents from traveling in it.

If you can locally source the correct quality of 2 conductor wire, save the shielded cable for a future use.
 
20200327_203608.jpg
Thanks for the input. Though, just thinking out loud, the "low" pin connects to the airframe ground and they don't necessarily specify whether that grounding should take place at a centralized grounding bus or if it permissible to take place locally near the instrument.

Undecided. Playing devil's advocate, fwiw.
 
Always ground at the device that provides the power.
 
I ran all shielded twisted pairs for all my GMU11s power/grounds (three total LRUs) using 22 gauge no regrets. All three were mounted in wingtips
 
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