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P-Lead wire routing question

Bill Wightman

Bill Wightman

Well Known Member
I'd like to know if any of you have experience running your mag P-leads in the same bundle with other instrument wiring. I'm aware of the voltage spikes (about 170 volts peak) the P-leads carry. The wires I will use are AWG-18, and very well shielded. Shielding will be grounded at the mag end only.

Proposed routing: My RV8 has several firewall forward transducers feeding a VMS-1000C that pass through the firewall in a big bundle together. Wanting to keep the mess to a minimum, I'm considering routing my Slick mag's P-leads through the same firewall grommet, where they'll remain bundled up with the VMS stuff for about 18" or so before diverging to the mag switches. Is this OK? The VMS manual only states not to bundle *ignition* wires with the transducer wiring, but this is a bit vague so I'm poking around for some feedback here.

I'm concerned about possible interference with the VMS transducer wiring if they're bundled together.

Bill
 
No problem after 2.2 hrs

I ran the p-leads in the same bundle with all my other wires (EGT, CHT, oil pressure, gas pressure, oil temp, alt. field) and no issues after the first 2.2 hrs. The P-leads were shielded. I did run the bus power from the battery through a different hole. Wish I had more hours to report more conclusively.
 
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I don't have a VMS in my instrument group, but have had no issues (of which I am aware) with the Dynon wiring etc. all of which goes through the same hole as the P-leads. P-leads are shielded of course. This after 33 hours.

greg
 
Greg Arehart said:
I don't have a VMS in my instrument group, but have had no issues (of which I am aware) with the Dynon wiring etc. all of which goes through the same hole as the P-leads. P-leads are shielded of course. This after 33 hours.

greg
Click to expand...

My P-leads are grouped with a many other wires coming through the fire wall and so far all is OK - including the radio, it sounds the same as before when there were no P-leads. (I mention this relative to having installed the P-leads with #18 wire to and from the mags with no shielding, I forgot they should be shielded. Again, so far, so good. The radio sounded good once I got the squelch under control.)

New flap motor installed, should be ready to launch again in a day or so. :)
 
In general if your P-Leads are properly assembled with shielded wire you shouldn't have any problems. That being said, on any RV that we finish, we will always run them separately through their own small grommet. It helps for future maintenance, and just is a bootstrap to ensure the system will be quiet.

Either way I think you'll be fine, but my personal preference would be to run them alone.

Cheers,
Stein
 
Thanks for the answers!

OK, I guess I'm gonna take the easy way out and run them together with the other wires. If I have any problems, I'll separate the P-leads out.

Frank, Greg, David and Stein: thank you for taking the time to help out. :D
 
Any more follow-up?

I'm wondering if running senor wires for my AFS (oil press, oil temp, fuel flow, CHT, EGT, etc.) with my left mag P-lead and other misc. 14v power wiring FWF will cause issues. Right ign is LS and P-leads come from VP-200 switch panel.

Also, should I run the wiring from my LS direct crank sensor by itself? Or is this a relatively 'quiet' harness to the LS ignition module? I'd like to run it with my right-side CHT/EGT wires.

I'm thinking the only 'really noisy' wires that run through the firewall are my LS primary ignition wires, which I will run completely separate from everything else. It sure would keep things tighter if I could run everything else as a single bundle through the firewall, then routed where it all needs to go. Is that a really bad idea, all things considered?

Like everybody here, I'd rather avoid issues now than have to change it later! And as always, thanks for any input you may have.
 
EGT and CHT sensor wires with Spark Leads

Another similar question for my installation. I have seen a few pictures of installations with the CHT and EGT sensor wires bundled with spark plug leads along the end of the cylinders. Is this OK or should it be avoided?

Thanks,

Rob
 
Since thermocouple...

justplanecrazy said:
Another similar question for my installation. I have seen a few pictures of installations with the CHT and EGT sensor wires bundled with spark plug leads along the end of the cylinders. Is this OK or should it be avoided?

Thanks,

Rob
Click to expand...

...outputs are in the millivolt range, and the sparks are in the kilovolt range, I would avoid this. It's a far greater variation than the earlier P-Lead discussion, and there is usually no need to do it...:)
 
EGT and CHT wire Routing

Does anyone have any good photos of how they routed and terminated their CHT and EGT's to avoid this scenario?

cheers,

Rob
 
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