Mag Grounds

[Jim P]

I'm sure this has been discussed but searching the archives didn't produce
a lot, so I wanted to request a clarification.

I'm wiring up two Slick mags with SPST switches. From the Z-13 diagram here
's how I understand the mag wiring:


1) Use 18AWG shielded wire

2) Connect the mag-side ground pigtail to the ground stud on the mag.

3) For switch side, connect the ground pigtail to the ground side of t
he switch, thus when the switch is closed, the mag grounds to the engine vi
a the mag, using the shielding for the ground path and negating a parallel
ground path.

Do I have this correct?

[az_gila]

Originally Posted by Jim P

I'm sure this has been discussed but searching the archives didn't produce
a lot, so I wanted to request a clarification.

I'm wiring up two Slick mags with SPST switches. From the Z-13 diagram here
's how I understand the mag wiring:


1) Use 18AWG shielded wire

2) Connect the mag-side ground pigtail to the ground stud on the mag.

3) For switch side, connect the ground pigtail to the ground side of t
he switch, thus when the switch is closed, the mag grounds to the engine vi
a the mag, using the shielding for the ground path and negating a parallel
ground path.

Do I have this correct?

Jim... that would be the best approach.... Some certified planes also ground the shields at the switch, but that violates a rule of shielding that says to only ground a shield at one end only.

This could be important, since when the engine is running, the P-lead is not connected to anything, but it can act like an antenna, with fast 300 volt pulses on the center wire. A shield here is a good thing....

I would do it the way you describe.

gil in Tucson

PS Try finding the P-lead wiring in a certified planes Maintenance Manual - it doesn't fall under "electrical" and doesn't fall under "engine".. the Piper and Cessna manuals I looked at just didn't show the actual wiring.