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Shielding for pmag wires

tomhanaway

Well Known Member
Do any of the wires (12v or p-lead) require/benefit from shielding? I'm not talking about wires to sparkplugs, only the wires to panel.

No indication of such in emagair's wiring diagram. Nuckolls mentions shielding for magnetos but that's a somewhat different animal.

Thanks,
Tom H.
 
No shielding is required. If you elect to add wires for the comm port into the cockpit, use twisted pair.

You can short the twisted pair together, which is the same as adding the jumper or connect to the P-mags with a PC using Emag's EICAD program to tune them or install an EICommander.
 
Shields

From page 7 of the current manual (114):

Note 1: If you are r
eplacing a magneto, your old P-Lead can serve this
purpose, and may already be wired to a
suitable switch. Take care that
magneto p-lead wire is shielded, and th
e shielded braid is a potential
(unintentional) short to
ground. Keep it clear of
connections and terminals.

I take this to mean that it is ok to use the existing p-lead in an upgrade, but make sure it is not inadvertently grounded.
 
When I replaced my mags with pmags, p leads were shielded. I just used the existing leads. No problems with mag operation or radio noise. So shielded cables work. Can not say about non shielded cables.
 
...

I take this to mean that it is ok to use the existing p-lead in an upgrade, but make sure it is not inadvertently grounded.
Correct.

The way the standard P-mag wiring works is to power the P-mags up when the Master is turned on. Then the ignition switch grounds them, just like a standard mag. Grounded, no spark, ungrounded, spark.

The difference with the P-mag is that when the P-mags are powered up and grounded, they are in "setup mode". Meaning that you can blow in the tube and set top dead center when they are powered up and grounded.
 
Bringing an old thread back from the dead...

I have an audio noise issue on my RV-8, and I've isolated a good bit of it as coming from my dual Pmag power leads, so I've been wondering if I should run new shielded power wires. But, in searching the forums I find posts like this;

No shielding is required.
So here is the conclusion for the books:
1. Spoke to Brad at E-Mag and he say the P-Mag DOES NOT NEED shielded wire.
2. Also spoke to Stein at Stein Air and he confirmed this.

So now I'm undecided whether I should waste my time running new shielded wires... here's the back story; for years my -8 had a caveman panel with a KX-125 navcom and an intercom. That was it... the "audio out" from the radio went to the intercom and all was well for 1500+ hours; mostly quiet with just a wee bit of strobe noise. But, 2 years ago I did a panel upgrade adding a GTR200 com along with a GNX375 GPS/xpdr. I didn't use a true audio panel, but instead used a Flight Data Systems AP-60 audio mixer. Now, I have noise, a crackly static type. I've isolated most of it to the Pmag power leads; in flight, I pull the Pmag power CBs and the noise is much reduced. So, there IS some noise from the Pmags, but is adding shielded wiring there barking up the wrong tree?

I did find one thing yesterday that I did on the original intercom install; I didn't use the isolating wafer washers on the headphone plugs. I did for the mic jacks as the intercom install drawing called for it, but not the headphones. I went ahead and installed new isolating washers for the phone jacks, but I'm unable to ops check it as my engine is currently missing a few (all...) cylinders... so before I tear into running new shielded wires, do y'all think that the noise might be caused by these missing isolators? Could it be that the new Garmin stuff plus the audio mixer bumped up the noise sensitivity of the system and these missing isolators sorta pushed it over the noisy edge?

I hope the new washers fix it, I really don't wanna waste a day running new wires...

Thanks!
 
Hey John - when we first started flying the RV-3 with the dual P-Mags, we had some static that we could make go away by shutting down one of the P-Mags. But it wasn’t the power - it was loose attachment of the plug wires to the plugs. We had a set of BR8-ES’s with the screw-on tips, and those were not tight. We replaced the plugs with the solid-ended ones, and have not had a problem since. not necessarily your problem…but something to check.
 
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