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P Lead Shield Ground

ntspdy

Active Member
During sound routine maintenance I noticed the shielding for the P leads on both of my slick mags isn’t grounded. Magnetos are still a bit of a magical box for me but my understanding was the shielding is supposed to be grounded at the mag side and floating at the switch. Is this correct and if so is the fix as simple as stripping back some sheath exposing the shielding then adding a ground strap to the ground screw next to the p lead on the mag?
 
Standard magneto wiring connects the points terminal to the magneto case via a panel switch. When the switch is closed, the points terminal is grounded. So, tie the center conductor to the points terminal and one switch terminal, and the shield braid to the case screw and the other switch terminal.

It's good practice to fixate the shielded P-lead at the magneto end. Easy to do with an adel. The case screw does double duty.
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The advantage of the method Dan noted is that in the event the engine ground strap fails, the P-lead won't become an engine ground.
 
I picked this tip up from Dan in 2012. it's a good practice. no issues. very robust. 996 flight hours.
 
iF YOU GROUND THE SHIELD AT THE MAG AND THE SWITCH, YOU WILL HAVE A LOT OF RADIO NOISE!!! Trust me on this... Ground the shield only at the Mag, not the switch. A rule of thumb... ground the shields nearest the point of power.

Regards,

DAR Gary
 
Radio Noise

iF YOU GROUND THE SHIELD AT THE MAG AND THE SWITCH, YOU WILL HAVE A LOT OF RADIO NOISE!!! Trust me on this... Ground the shield only at the Mag, not the switch. A rule of thumb... ground the shields nearest the point of power.

Regards,

DAR Gary

No radio noise whatsoever here using the Bob Nuckols Aeroelectrc Connection method like Dan posted above.

Skylor
RV-8
 
iF YOU GROUND THE SHIELD AT THE MAG AND THE SWITCH, YOU WILL HAVE A LOT OF RADIO NOISE!!! Trust me on this... Ground the shield only at the Mag, not the switch. A rule of thumb... ground the shields nearest the point of power.

Regards,

DAR Gary

Correct, shields should be grounded at one end only. With DanH's suggested solution, when the aircraft is running, the switch is open. That means that the shield is only grounded at one end, as you and most people recommend. All good.
 
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