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P-lead wire routing

mdud

I'm New Here
I have a single mag and LSE. I'm running wiring through my firewall penetrations and I have some concern about the routing of the P-lead. I want to keep electrical noise out of engine monitor sensor wiring and the audio. I have a separate firewall penetration for the LSE RG-400 leads to the coils and I am planning on running the P-lead through the same opening. On the inside of the firewall I am not sure I should run the P-lead in the wire bundle routed to the instrument panel or keep it some distance away with a different routing. Any thoughts?
 
Shielded wire?

If you’re running properly shielded wire, you’ll likely be fine regardless of where you run it. Technically there’s little or no current on a p-lead in normal operation, creating little if any field. However, if you can run it away, or run it with high power or otherwise insensitive wiring, it’s lower risk. I ran one firewall penetration with powered stuff and main bus power, and another about six inches away for all the signal wiring FWF. My p-leads were shielded. Another effective practice is if signal and power must cross, route them such that they cross perpendicularly. It might cause the routing to look a little funny/sloppy, but some CAN related vehicle experience has proven it to work really well. Same rules go for audio/radio. YMMV.
 
Flew about 500 hours with two p-leads in the single wiring bundle. No issues with the GRT EIS or the audio.

BTW, no flopping p-leads please.

P%20Lead%20Fixation.jpg
 
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plain metal clamp?

while replacing a mag today I managed to break the ground wire. This was mainly due to improper support of the mag wires, so I searched up this very helpful photo and description by DanH.

I'm curious, however, as to why the clamp needs to be plain metal? Couldn't a normal adel clamp be used there? I've used them in many places around the engine compartment with no issues. I'm assuming there's a good reason in this case for plain metal so I'll appreciate the explanation.

thx

Flew about 500 hours with two p-leads in the single wiring bundle. No issues with the GRT EIS or the audio.

BTW, no flopping p-leads please.

P%20Lead%20Fixation.jpg
 
I'm curious, however, as to why the clamp needs to be plain metal?

It doesn't, strictly speaking. A rubber lined adel will work IF the correct size is selected. The plain one is more compact, and easier to handle when fumbling with the wire and the little magneto ground screw.
 
thanks, Dan. I'll see what I've got in the Big Bag of Clamps.

and I'm just realizing that I'll need to cut off my newly-added ring terminals so I can add the heat shrink as you show in the photo. sigh.
 
thanks, Dan. I'll see what I've got in the Big Bag of Clamps.

and I'm just realizing that I'll need to cut off my newly-added ring terminals so I can add the heat shrink as you show in the photo. sigh.

I'd just wrap it with a little rescue tape rather than cut and recrimpt.
 
Having seen a case where there was an electrical short in a certified aircraft that involved a wire bundle which also contained the P-leads, and which then grounded of both P-leads after the wire insulation melted and caused a forced landing, I would avoid running the P-leads in a bundle.
 
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