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Slick Mag Termination

DarylT

DarylT

Well Known Member
Can someone show me a picture of how to terminate the wire at the magneto side for a slick mag? All I have ever seen is Bendix and it has a connector that the wire slides into and screws down. It would seem to me on a slick to terminate the center wire with a ring connector to go on the Plead lug. Then ground the shield to somewhere on the mag. There is a screw on the mag case. Is that an ok place to attach the sheild to?
 
You have it right Daryl - your P-Lead should be a shielded wire - terminate the core of the lead with a ring connector and attach it to the post on the Mag. Terminate the shield in another ring connector using your favorite method (Knuckoll's has some great pictures), and attach it to the ground screw on the mag. No pictures handy, but you described it well enough that you have it right.

Paul
 
This is what the P-Lead should look like:

SS1.jpg


Cheers,
Stein
 
SteinAir said:
This is what the P-Lead should look like:

SS1.jpg


Cheers,
Stein
Click to expand...

I bought some of these and they are slick. But please note, the other end of the shield has to be grounded to the center pole at the switch to make it work.

Some instructions regarding a shield instruct to gound only one end of the shield. If the shield is being used as the conduit for grounding the mag, it must be grounded on both ends.
 
David-aviator said:
I bought some of these and they are slick. But please note, the other end of the shield has to be grounded to the center pole at the switch to make it work.

Some instructions regarding a shield instruct to gound only one end of the shield. If the shield is being used as the conduit for grounding the mag, it must be grounded on both ends.
Click to expand...

Don't do that!! Don't use the shield as the ground, that is what the center conductor of a P-Lead is for to begin with. There is no good reason that I can think of to terminate both ends of a P-Lead shield when using shielded wire. The center conductor is the P-Lead - the Shield is NOT what you use for grounding the mag!!! If you do it that way Bad Ju-Ju will ensue (and lot's of weird whining/whooping/scratching noises in your electrical system). :)

If you're using the shield for the "ground conduit" David, then what are you using the center conductor for?

Cheers,
Stein
 
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SteinAir said:
Don't do that!! Don't use the shield as the ground, that is what the center conductor of a P-Lead is for to begin with. There is no good reason that I can think of to terminate both ends of a P-Lead shield when using shielded wire. The center conductor is the P-Lead - the Shield is NOT what you use for grounding the mag!!! If you do it that way Bad Ju-Ju will ensue (and lot's of weird whining/whooping/scratching noises in your electrical system). :)

If you're using the shield for the "ground conduit" David, then what are you using the center conductor for?

Cheers,
Stein
Click to expand...
Stein,
He is probably doing what a lot of builders do. Connecting the shield to the ground lug on the ignition switch(s) and to the ground screw on the mag. Thus the shield becomes the ground source for the ignition switch. I have seen many older standard category certificated airplanes wired this way.
I am very much against it not only because of the ground loop noise issues it can cause but because of the danger involved. Many builders just use a pig tail of teh shield to make the connection. With age the shield can be vulnerable to breakage much more than the center conductor wire (even if it has been heat shrinked). If the shield breaks, you no longer have a ground source to disable the mag.
The best way is to do it as shown in Steins photo and only connect the shield
to ground at the mag. end. Source a separate ground for the ignition switch(s).

Oh...and do a safety check on a regular basis. With the engine at slow idle, momentarily switch both mags off to verify they are being disabled. This is best done just before shutdown after a flight...then you know whether something broke during that flight.
 
DarylT said:
Can someone show me a picture of how to terminate the wire at the magneto side for a slick mag? All I have ever seen is Bendix and it has a connector that the wire slides into and screws down. It would seem to me on a slick to terminate the center wire with a ring connector to go on the Plead lug. Then ground the shield to somewhere on the mag. There is a screw on the mag case. Is that an ok place to attach the sheild to?
Click to expand...

The later model slick mags have a ground symbol next to the screw intended for this purpose.
 
alpinelakespilot2000 said:
OK-I thought we just had this discussion last week. http://www.vansairforce.com/community/showthread.php?t=36272&highlight=mag+wiring

Now I'm thoroughly confused. Scott and Stein, are you arguing that Bob Nuckoll's suggestion is wrong, or is it a different point you are arguing?
(See page three, View A, of the link below for Bob's wiring diagram.)
http://www.aeroelectric.com/articles/MagnetoSwitchOptions.pdf
Click to expand...

I wasn't familiar with Bob's suggestion so I took a look at it. Yes, in my opinion he is wrong for the reason I suggested previously. I have first hand experience with a hot mag on a couple different airplanes because of a failure of the shield (no one was hurt though).
I recommend a separate wire between the ground lug on the switch(s) and the common ground connection point of the airplane. I use an 18Ga wire so that it is durable and will have a very low likelihood of breakage.
 
I also strongly 2nd Scott's comments and strongly agree. I too have fixed bad shield that were hooked up this way after people found broken shields. Granted it's more prevalent with the old "crimp a terminal to the woven shield" than the solder splices, but it still happens. Also, given the fact that shields are notorious "gatherers" of electrical noise I'm do not like to see it done that way. Additionally there is a HUGE variation in how people wire up their planes, what brand keyswitches they use, so on and so forth....So, to me the only good way to do it is to use the single point ground, and then only ground one end of the shield.

It's just my 2 cents, and I follow most of Bob's lessons, but in this case I squarely disagree. I guess we each get our own opinion! :)

Cheers,
Stein
 
So does this mean...

SteinAir said:
Don't do that!! Don't use the shield as the ground, that is what the center conductor of a P-Lead is for to begin with. There is no good reason that I can think of to terminate both ends of a P-Lead shield when using shielded wire. The center conductor is the P-Lead - the Shield is NOT what you use for grounding the mag!!! If you do it that way Bad Ju-Ju will ensue (and lot's of weird whining/whooping/scratching noises in your electrical system). :)

If you're using the shield for the "ground conduit" David, then what are you using the center conductor for?

Cheers,
Stein
Click to expand...


...you are relying on just internal, oily metal on metal contact for ground at the magneto end?
Or is there a seperate physical wire link from the magneto ground terminal to some other good ground spot?

As I said in the other thread... you might be introducing more single point failure points in the system as you try to remove a single one.
 
az_gila said:
...you are relying on just internal, oily metal on metal contact for ground at the magneto end?
Or is there a seperate physical wire link from the magneto ground terminal to some other good ground spot?

As I said in the other thread... you might be introducing more single point failure points in the system as you try to remove a single one.
Click to expand...

I'm not trying to argue my point Gil, just offering my opinion from experience.
I have seen failure of numerous P lead wires over the years. It is a small wire subject to engine vibration and other harsh environments. I recommend a heavier than needed switch ground wire to make it durable and unlikely to fail. Considering the much different environment it is routed in and not being connected to an object that is in constant motion, I feel it has an extremely low probability of failure.
As for "just relying on just internal, oily metal on metal contact for ground"...I don't think it is as bad as you imply. Whether it is or not, I would rather take a chance on a ground that has a few ohms of resistance than chance on not having one at all when I need it most.
As always...just my opinion. Everyone should do the research and decide for them self what they are most comfortable with.
 
Point taken....

rvbuilder2002 said:
....
As for "just relying on just internal, oily metal on metal contact for ground"...I don't think it is as bad as you imply. Whether it is or not, I would rather take a chance on a ground that has a few ohms of resistance than chance on not having one at all when I need it most.
As always...just my opinion. Everyone should do the research and decide for them self what they are most comfortable with.
Click to expand...

However, if you are using this method, then the addition of a short wire from the magneto grounding screw to the engine ground braid attachment point would be a worthwhile safety addition for very little extra effort or expense...
 
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SteinAir said:
Don't do that!! Don't use the shield as the ground, that is what the center conductor of a P-Lead is for to begin with. There is no good reason that I can think of to terminate both ends of a P-Lead shield when using shielded wire. The center conductor is the P-Lead - the Shield is NOT what you use for grounding the mag!!! If you do it that way Bad Ju-Ju will ensue (and lot's of weird whining/whooping/scratching noises in your electrical system). :)

If you're using the shield for the "ground conduit" David, then what are you using the center conductor for?

Cheers,
Stein
Click to expand...

I think, Stein, others have pointed out that what I was referring to is an FAA approved method of grounding the P lead to the magneto via the shield wire and the center ground poll in a typical magneto switch. One end of the shield is grounded to the magneto at the ground screw, the other is connected to the center pole at the switch which is connected to the P lead wire any time a mag is supposed to be off.

At one point in my varied and sundry life I had a notion to acquire an A&P certificate and worked as an apprentice in a repair shop toward that end. I too thought that using the P lead shield as the source of ground for the P lead was a rinky dink way to do it, but that's how it was done, 1960-70 vintage Piper Cherokees were wired that way. Part of the annual inspection was to check its integrity and that it worked.

That's why I think your soldier shield devices are so cool - so much better than crimping a connector on to the braided shield material.

I think though at this point, since there is so much consternation over this matter, I will leave my mag wiring as is just to see how much interference there is with no shield wire. I have 18 gauge wire to the P lead and 18 gauge wire from the mag ground terminal back to the center pole on the Van's mag switch.

I will give you-all a report on the interphone and radio noise, if there is any when I crank this thing up. :)
 
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