Magneto P-Lead Shielding

[nobubbles63]

i am in the process of dealing with a possibly poorly left mag. In checking mags, wiring and ACS ignition switch, I have a related question...I have seen various schools of thought on the shielding of the p-leads. I believe Aeroelectric and others suggest that in addition to being connected to the mag (done) that the p-lead shield is attached to the GND at the switch. The switch GND is NOT then connected to the aircraft frame.
Mine is not, the shields are not attached at the switch, and GND is to airframe as per ACS switch instructions. I didn't do the build.
I'm going to change it to the alternative and hoping this is the "better" arrangement..any advice to the contrary?

[RV6_flyer]

Originally Posted by nobubbles63

i am in the process of dealing with a possibly poorly left mag. In checking mags, wiring and ACS ignition switch, I have a related question...I have seen various schools of thought on the shielding of the p-leads. I believe Aeroelectric and others suggest that in addition to being connected to the mag (done) that the p-lead shield is attached to the GND at the switch. The switch GND is NOT then connected to the aircraft frame.
Mine is not, the shields are not attached at the switch, and GND is to airframe as per ACS switch instructions. I didn't do the build.
I'm going to change it to the alternative and hoping this is the "better" arrangement..any advice to the contrary?

I like to have the shield attached to the mag (ground) and then to the switch. The only ground on the switch is the shield back to the mag. IF the shield connection breaks at either end, the mag will NOT shut off.

IF you also tie the shield at the switch to the airframe ground AND at some point in the future have the ENGINE GROUND path open up, all the current will go through the shield (burning up the wire) and the shield will act as a fuse. The worst case is the ignition P-lead shield acting for ground path of the starter with a large amount of amps trying to flow through the path. The alternator could also use the P-lead shield as its ground path with whatever current it is producing having its return path through the P-lead shield.

Just my opinion and it may only be worth what you paid for it.

[DanH]

Isolated circuit, no airframe connection. And for goodness sakes, support the wires at the mag end.
.

[nobubbles63]

Thanks for the replies...looks like what I have read is the way to go...ground shield at both ends but remove the switch ground to airframe.
Derek

[lr172]

Originally Posted by nobubbles63

Thanks for the replies...looks like what I have read is the way to go...ground shield at both ends but remove the switch ground to airframe.
Derek

Just to clarify, the shield goes to the mag grd on the mag side and on the switch side, the shield goes to the second pole of the switch, not a ground.

[Cannon]

Grounding the p-lead to the airframe can also lead to comm issues. I had pretty bad static on both comms of my Cessna. The p-leads were grounded both through the shields AND to the airframe. Once I removed the wire that grounded the mags to the airframe, the problem was 100% eliminated.

[nobubbles63]

Thanks for the suggestions....will be re-wiring the switch and grounding the shields as suggested and have clips on order to support the p-leads.
Derek