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1. 06:06 AM - Re: Re: wire for mags (Charlie England)
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Subject: | Re: wire for mags |
On Tue, Jan 3, 2017 at 9:53 AM, Denny Baber <baberdk@gmail.com> wrote:
> I agree with the wiring description and it is electrically correct. But
> since we have the center conductor attached to the mag, and the mag is
> producing the electrical interference, wouldn't it be safer to connect the
> shield at the switch end so the shield on the cable follows the plane
> ground instead of the mag ground?
>
>
> Respectfully,
> Dennis Baber
> (305) 814-7218
> baberdk@gmail.com
>
> Stay Curious
>
Hi Dennis,
Sorry to take so long to reply; for some reason this entire thread ended up
in my gmail spam folder.
The P-lead shield should *always* be connected to the case of the mag. The
mag is the source of the noise, so you're grounding the shield at the
ground reference of the noise source. But for me, an even more important
point is that the shield is how you turn the mag 'off'; it supplies the
ground path to short out the coil of the mag when you turn the mag off. If
it has to find its ground path through the airframe back to the mag, what
happens if a tech is doing maintenance around the engine and removes the
battery negative lead(s)? Depending on how the ground wires are arranged
from airframe to battery and from engine to battery, it can leave the mags
'hot' without the tech realizing it (he hasn't touched the mags or mag
switches). That can be deadly.
There's also some chance that if you route the shield's ground path through
the airframe, you may inject the noise into the ground path of other
electronics in the a/c, similar to what happens when the strobes'
"whoop...whoop" sound is heard in the intercom.
Charlie
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