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GTP59 Shield Wire

TASEsq

Well Known Member
Patron
Planning my wing wiring and notice that the G3X manual on page 21-3 calls for the sheild of the GTP59 wire to be attached to a 16 AWG wire and then the backshell.

I would like to split this cable at the wing root with a CPC connector - but the 16AWG wire will mean it needs to go into large pin connector.

I notice the power wire to the temp probe is not anywhere near this big - does anyone know why i cant use a 22AWG wire for this shield pass through the connector (and at the dsub end to the AHARS)?
 
That has to be a misprint. There is no electrical reason for a 16 AWG wire for the shield drain wire. That?s pitot heat size! 22 AWG would be fine.
 
My harness

I had my wing harness built by a top shop who advertises on here and they did not use 16awg; they used something smaller. If I had to guess, it would be 22awg
 
Weird...but..

I agree - this is a shield wire, not a DC return or common.

However, instead of a single 16AWG to carry the shield - use two 20AWG (or 22AWG) wires in your connector.

Just a thought.


Cheers!
 
Best not run it through a connector at all, the shield on the GTP is a heavy double shield probably for good reason.
 
And...

And it is a factory cable.

According to the avionics shop, lots of people cut/extend/shorten this cable...
 
Best not run it through a connector at all, the shield on the GTP is a heavy double shield probably for good reason.

The other reason for this question, is i was thinking of putting the probe in the left wing - where the pitot tube hole will be in the skin. I wanted to be able to run the cables in the wing now, to save fishing it through the wing later. I was figuring a connector at the probe would be a good idea anyway in case the probe ever needed to be removed?

In the install manual they talk about extending the cable up to 25ft is fine, and it calls for “three wire twisted shielded cable” - but unfortunately doesn’t recommend a gauge.

The gtp59 isn’t listed in the current draw table on page 2-14 but I would imagine it doesn’t draw anything. I was thinking a 22awg would have been fine? https://www.steinair.com/product/22-ga-3-conductor-shielded/

Here’s one from a citrus g1000 install - looks like 20 or 22 awg maybe in that little connector?
s-l640.jpg
 
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The other reason for this question, is i was thinking of putting the probe in the left wing - where the pitot tube hole will be in the skin. I wanted to be able to run the cables in the wing now, to save fishing it through the wing later. I was figuring a connector at the probe would be a good idea anyway in case the probe ever needed to be removed?

In the install manual they talk about extending the cable up to 25ft is fine, and it calls for ?three wire twisted shielded cable? - but unfortunately doesn?t recommend a gauge.

The gtp59 isn?t listed in the current draw table on page 2-14 but I would imagine it doesn?t draw anything. I was thinking a 22awg would have been fine? https://www.steinair.com/product/22-ga-3-conductor-shielded/

Here?s one from a citrus g1000 install - looks like 20 or 22 awg maybe in that little connector?
s-l640.jpg

When I read the Garmin G3x install manual this morning, I thought it said that all wires are 22awg unless otherwise noted. JMHO YMMV
 
Does anyone know if Garmin has a support email where you can ask these kinds of questions?
 
I suspect why they called out #16 wire for the shield attachment is since they are referring to the crimp terminal attachment. This allows the wire to be crimped onto the wire easily, it?s not due to current carrying capability. #22 wires don?t work to well in crimp ring terminals.
 
I suspect why they called out #16 wire for the shield attachment is since they are referring to the crimp terminal attachment. This allows the wire to be crimped onto the wire easily, it?s not due to current carrying capability. #22 wires don?t work to well in crimp ring terminals.

Interesting thought - but why not use a red terminal instead?
 
GTP 59

The other reason for this question, is i was thinking of putting the probe in the left wing - where the pitot tube hole will be in the skin. I wanted to be able to run the cables in the wing now, to save fishing it through the wing later. I was figuring a connector at the probe would be a good idea anyway in case the probe ever needed to be removed?

In the install manual they talk about extending the cable up to 25ft is fine, and it calls for ?three wire twisted shielded cable? - but unfortunately doesn?t recommend a gauge.

The gtp59 isn?t listed in the current draw table on page 2-14 but I would imagine it doesn?t draw anything. I was thinking a 22awg would have been fine? https://www.steinair.com/product/22-ga-3-conductor-shielded/

Here?s one from a citrus g1000 install - looks like 20 or 22 awg maybe in that little connector?
s-l640.jpg

As Walt mentions, there is a reason the GTP 59 is fabricated the way it is. The use of a heavy gauge shield termination is not a mis-print in the manual. As a small metal appendage to the outside of the airframe, we had to design the connection from the GTP 59 accordingly to prevent the GTP 59 from becoming a HIRF/IEL path to the rest of your avionics. I do not recommend deviating from our guidance on this.

Steve offers some pretty good information in this post that I think is relevant to the discussion on this thread as well, in case you are interested. The discussion specifically mentions a suggestion on how to deal with the wiring of the GTP 59 from the wing to the GSU 25.

Please let us know if you have any other questions. You may reach out to us directly at [email protected] with any questions as well.

Thanks,

Justin
 
Thanks for the info Justin,

By HIRF/IEL do you mean getting struck by lightning?

So would there be any issues with cutting the GTP59 cable at the wing root and soldering on a 16awg pigtail and passing this through a pin? (and same on the other side of the connector?

If i wanted to run the cable before hand, instead of using the one that comes with the probe, can you advise what spec the cable is? (is it some kind of larger AWG shield to require a 16awg pigtial?). The g3X manual says the GTP59 cable can be extended, but does not give any clues as to what to use for this extension.

I had read that forum previously - but in my case i really want to be able to disconnect all wires from the wings easily - so had planned a wing connector in any case, was just trying to put the GTP59 wiring all in the same plug - for a 16AWG for this shield i will have to put it through the same CPC as the power pins for other devices (Series 2 CPC can't handle 16AWG as far as i know).
 
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The GTP 59 is certified on business jets with Garmin Avionics such as the G3000 or G5000 systems. A part must meet the highest level of certification for where it is used. It is not us single engine piston guys driving the design.

Your experimental aircraft is less likely to get struck by lightning than a business jet, but it is still a good idea to follow best practices of maintaining the shielding of the GTP wiring harness. When necessary I use standard MIL 27500 shielded wire to extend the wiring. I typically do not wire through a connector, but splice the shield directly together.

Except for the RV-12, if you have to pull the wings, it is a major project. I personally would rather just have a small service loop of wires in the wing root. If you ever pull the wings off, you can cut the wires and splice, or put a connector on at that point. Remember that any connector is a possible failure point.

-Levi
 
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