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Dumb GTX330 Wiring Diagram Question


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Helping my A&P finish up the harness for my 330 and I had a question for you guys and gals.  Looking at the wiring diagram in the manual, see snip below, my interpretation is they want you to run two separate 22AWG wires to the 5A breaker for power.  Same for ground, I am guessing for redundancy?   At first he wanted to splice the two pins together and use one main wire...then suggested using a 2 conductor wire.  He admitted that most of the transponders he has installed, older stuff or the Stratus ESG, only call for one wire each and suggested I reach out to Garmin since avionics are not his specialty.  Since this is the last "stumbling block" to getting the wiring done (the rest of my harness was built by an avionics shop) I thought I'd ask for help here.  Seems straight forward to me (use two, separate wires), but I know there are some avionics experts on here and was hoping to get an answer so we can do this tomorrow. 

Thanks!

 

Note:  Not talking about Power 1 and Power 2.  I take it that is for aircraft, like twins, with dual power sources.  This is just asking about pins 21/42 and 27/43.  

TwuEkA4.png?1

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If you follow the drawing...

You get exactly what the manufacturer has tested...

This removes the chances of making a mistake... causing getting a different result than what the manufacturer has tested...

It may be the same...

Or it could be different....

Great question...

How do you feel about it?  (Or, removing feelings, what does logic provide for you?)

PP thoughts only not an avionics tech...

Best regards,

-a-

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So....I guess I don't do a very good job of conveying the ideas in my head.  My question in a different, more concise way: is running two wires to the breaker, and to ground, what the manufacturer is trying to tell me with this drawing and is that how an avionics tech would read it.  Because that is my gut feeling, but when I ask the three A&Ps on the field I get all sorts of answers....

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You gots to read all the various notes...:) For a 14V system you are going to be drawing more amps than a 28v system so they want you to use 2 of those little pins and either 2 wires as depicted or you could use a larger wire size to the connector and splice the 2 together. What revision of the install manual are you referencing? It looks older. 

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Communication is such a two way street...

Without readbacks and feedback it is easy to miss a subtle mistake... or have a mis-understanding...

In this case... the notes about 14v vs. 28v....

 

Our planes went 24v to save on the weight of wiring...

It is interesting how a dual use (12/24v) device needs to be wired safely for the environment it is attached to...

The fine details that an avionics tech is very familiar with...

 

Even with a modern 24v system... you will probably find some 12v devices on it, with a voltage balancing resistor generating heat next to it... :)

 

We have a few avionics gurus around here...

Best regards,

-a-

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15 minutes ago, JimB said:

You gots to read all the various notes...:) For a 14V system you are going to be drawing more amps than a 28v system so they want you to use 2 of those little pins and either 2 wires as depicted or you could use a larger wire size to the connector and splice the 2 together. What revision of the install manual are you referencing? It looks older. 

^^This.

Only one wire from the device to the breaker is needed, and it's better to just run one wire in several ways.    It can be split right at the connector at the device to go to both the indicated pins.

Often this is due to current limitations either on the input pins or on the circuit board behind it, but the wire from the device to the breaker just needs to be big enough to handle the current.

 

 

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@JimB  I have an old revision, F from 2004, because that's all my Google-Fo could find and Garmin does not have it up on their website from what I can see.  Any other tricks to find newer revisions? But yeah, your comment makes sense to me: sounds like it's more of a pin limitation due to the current needed @ 14V.  

So another dumb question; from my reading, the Garmin High Density D-sub pins can support 22-24 Ga wire.  How would you run a larger single wire (say 18 or 20ga) to that? Run the wire then solder sleeve or butt joint two 22awg wires (with pins) onto the larger wire? 

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No dumb questions. 

25 minutes ago, TCUDustoff said:

Run the wire then solder sleeve or butt joint two 22awg wires (with pins) onto the larger wire? 

That it. This is from a GTR/GNC manual but you get the idea. You can certainly run two separate wires to the connector too if you want. 

image.thumb.png.ecb5eb8f84595df08c217ea5e5bdc151.png

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@JimB Perfection.  Makes total sense to me.  I'll talk to my A&P and see what he is more comfortable with "signing off," but ensure there is enough conductor paths that meet spec in the final "decision."  One last question while I have you....when you look at a Garmin manual for say Canbus, is the idea here to use a two conductor shielded wire? The guys on the field with RVs that did experimental all swear you have to use a separate wire for CAN-H and CAN-L and I'm just here like "did you even look @ the wiring diagram?  Pretty sure it wants you to use a 2-conductor shielded wire...." My wiring  harness was pre-made, but if I ever want to add in the OAT gauge I'd need to modify it hence my question. 

 

6MzSkuv.png

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What does flag notes 3 & 5 say ? I have heard several iterations on what type of CAN Bus wire should be used. It seems that it  changes depending on  if you are installation GFC500 autopilot and what revision of the installation manual that your are using.  One avionics shop told me that  the latest G5 manual  they have gone back from using the expensive 3 to 4 dollar a foot extra shielding cable. I haven't confirmed that.  LPM I believe is the lighting protection module and heard that Garmin was going away from that if I recall my conversation  with Garmin correctly.

I guess my point is that the installation manual is  constantly be revised so you may find several answers  when it comes to which CAN bus cable is the  correct one.

James '67C

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19 hours ago, TCUDustoff said:

Run the wire then solder sleeve or butt joint two 22awg wires (with pins) onto the larger wire? 

FWIW, many prefer crimped butt connectors since solder can crack under vibration.   This goes for any connector or joint.

 

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12 hours ago, TCUDustoff said:

One last question while I have you....when you look at a Garmin manual for say Canbus, is the idea here to use a two conductor shielded wire? The guys on the field with RVs that did experimental all swear you have to use a separate wire for CAN-H and CAN-L and I'm just here like "did you even look @ the wiring diagram?  Pretty sure it wants you to use a 2-conductor shielded wire...." My wiring  harness was pre-made, but if I ever want to add in the OAT gauge I'd need to modify it hence my question. 

You can use either MIL-C-27500 or the 120 ohm Can Bus shielded 2 conductor wire. However if you are planning to install a GFC 500, it is preferred to use the 120 ohm Can Bus wire. In the big scheme of installing things the 120 ohm wire is not that expensive 

https://www.aircraftspruce.com/catalog/avpages/garmin_11-17264.php?clickkey=135505 

G5 install manual

image.thumb.png.2fbd9e9d24a758bd8e5065b7d38712e5.png

GFC 500 manual

image.thumb.png.9ae98a72d5e5d9e70fae348e91426604.png

Edited by JimB
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The most recent manual for the G5 states that twisted shielded pair can be used for the CAN bus with recommendations for 120 ohm CAN bus wire for the following three conditions:

1.  If the maximum CAN bus length of 85 feet is reached.

2.  If there are plans to install a GFC 500.

3.  If there are plans to install a G3X Touch. 

In the middle of 2020, the GFC 500 manual was updated and the 120 ohm CAN bus wiring became mandatory for new installs.

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On 3/14/2021 at 5:09 AM, jamesm said:

 One avionics shop told me that  the latest G5 manual  they have gone back from using the expensive 3 to 4 dollar a foot extra shielding cable. I haven't confirmed that.  LPM I believe is the lighting protection module and heard that Garmin was going away from that if I recall my conversation  with Garmin correctly.

 

Interesting...

I recently bought the G5 and comes with LPM. Flag note 5 references detail wiring of it on separate schematics. As for CAN wire Jim and Warren already explained.

FYI, current Install manual is Rev 24 Or at least it was when I started this install. ;)

Regards,

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TCU,

Wait till you install a GTN 650/750.   There are 4 power and 4 ground wires to pin out.  Of course you can tie together with a larger guage once out of the connector but to get power and ground on the unit its 8 pins. 

 

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  • 4 weeks later...

Sorry for not getting back to the group sooner; I got distracted with my 1941 Taylorcraft project :)

I've been reading up on all the pertinent ACs I can find, including AC 21-99, but have yet to find (or missed) my latest questions; assuming you can run both (in my case) 22 AWG wires into one butt joint to connect to a larger 20 or 18AWG wire to ground / power, how do you size the joint?  I haven't found clear guidance on how you size the joints for MULTIPLE wires vs the single wire range its sized for. 

Same thing applies to daisy chaining wire shields: the Garmin manual states how to do it with multiple solder braids, but what if you are using wires? Can you put two 22AWG ground wires in one solder sleeve, for example, to join three wires/shields?  Just trying to find the source material that calls out these kind of practices because the average A&P sure doesn't seem to know... In this case, knowledge is ALWAYS power (and its good to know so I can apply it to my car projects as well!) 

 

Oh, and some photos of my successful work for bragging rights.  Not bad for a "NASWHOLE" Nasa Engineer :p  100% better than the soldered junk they had before (where they IGNORED the call outs for shielded wiring, installed a resistor across the vox pot pins, and didn't use both grounds *sigh*)

 

XBP1VP3.jpgOTVFUM8.png

 

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3 hours ago, TCUDustoff said:

Sorry for not getting back to the group sooner; I got distracted with my 1941 Taylorcraft project :)

I've been reading up on all the pertinent ACs I can find, including AC 21-99, but have yet to find (or missed) my latest questions; assuming you can run both (in my case) 22 AWG wires into one butt joint to connect to a larger 20 or 18AWG wire to ground / power, how do you size the joint?  I haven't found clear guidance on how you size the joints for MULTIPLE wires vs the single wire range its sized for. 

Same thing applies to daisy chaining wire shields: the Garmin manual states how to do it with multiple solder braids, but what if you are using wires? Can you put two 22AWG ground wires in one solder sleeve, for example, to join three wires/shields?  Just trying to find the source material that calls out these kind of practices because the average A&P sure doesn't seem to know... In this case, knowledge is ALWAYS power (and its good to know so I can apply it to my car projects as well!) 

You can use crimp terminals and crimp butt splices as well, and they're preferred by many over soldered connections since the solder is subject to cracking under vibration and the crimps offer a little better strain relief.   The main thing with crimp terminals and splices is to use the proper ratcheting-type crimper. 

AC 43.13 Chapter 11, section 13, p 11-65 talks about splicing.   It mentions (in par 11-167 (f) ) that a splice can be used to join multiple wires to a single wire, but doesn't really say much about sizing.   For the most part, guidance on many electrical topics gives a lot of room for variations in practices, and you'll see different shops or people do things differently.   Since many splicing technologies (crimped, soldersleeve, etc.) generally size splices to cover a range of wire sizes, it probably won't be difficult to put two smaller wires in a splice sized for the larger wire.   If it is, maybe go up one size.   I don't know of any definitive guidance one way or other.

Edit:   AC 21-99 is Australian CASA, but it does say in Ch 6 Par 41 on Multi-Splicing to reference Table 6-10 for circular mil area of the combined wires.   Using stranded wire I take this to mean that, according to the table, two AWG 22 wires would be 2x754 = 1508, which is between the AWG 20 and 18 cross sections.   Since the red connectors and terminals are sized for AWG 18-22 it seems like two AWG 22 and a 20 or 18 would be appropriate for them.

Edited by EricJ
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Thanks to everybody, BTW, for your help; I have learned a-lot and even impressed the old timer avionics guy on the field when I had him inspect what I had done this morning (he was actually there and not out fishing!).  He gave me some pointers, and helped me tidy a few things up, but its passed muster so far!

I was hoping, however, you guys and gals can help me with one more question; I want to make sure I hook this up to my 430W correctly to ensure future 330ES upgradability later this year.  I have various versions of the 330 and 430W install manual, but none specifically mention the 330ES and they are all old.  Based on how the pre-made 430W/G5 harness came from the avionics shop (two conductor RS-232, two conductor AIRINC, and Annunciate E), and reading into the 430W install manual, I am assuming the following:

  1. I want BI-DIRECTIONAL RS232 between the units.  It's funny, because older versions of the transponder install manual have RS-232 IN from the 430W as the only wire, but the 430W install manual has it reverse (altitude in from the 327/330 as the only RS-232 link).   Anyways, I think the 430W will output WASS GPS position to the 330ES via RS232 (ADSB-Out+ protocol) and the 330 will send altitude info to the 430W (via Icarus-alt protocol).
  2. I have one set of AIRINC wires and Annunciate E. This gives me two choice, I think:
    1. Use the AIRINC as an out from the 430W and an IN on the 330 and use it to auto-start the flight timer and place it into ALT / GND.
    2. Use the AIRINC as an out from the 330 and an IN on the 430W to get TIS-A traffic on the 430W.  This requires using the Annunciate E as TIS Select. 

My understanding is that TIS-A is being discontinued, so I am leaning towards the other option.  Then again, I live in Houston so perhaps its worth while since I am in congested airspace that will probably continue to support it for a while? 

Thanks for the help y'all! 

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RS232 in is required from the 430.  Out is required if you use the “GNS” interface format, not required otherwise.

ARINC out transfers the TIS-A traffic to the 430.  You also need the TIS connect select (Pin 11, P1001 on the 430).

The Air/ground input is not ARINC but a discrete input on Pin 17.

Hope that helps.  Good luck.

Warren

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On 3/13/2021 at 7:49 AM, TCUDustoff said:

Helping my A&P finish up the harness for my 330 and I had a question for you guys and gals.  Looking at the wiring diagram in the manual, see snip below, my interpretation is they want you to run two separate 22AWG wires to the 5A breaker for power.  Same for ground, I am guessing for redundancy?   At first he wanted to splice the two pins together and use one main wire...then suggested using a 2 conductor wire.  He admitted that most of the transponders he has installed, older stuff or the Stratus ESG, only call for one wire each and suggested I reach out to Garmin since avionics are not his specialty.  Since this is the last "stumbling block" to getting the wiring done (the rest of my harness was built by an avionics shop) I thought I'd ask for help here.  Seems straight forward to me (use two, separate wires), but I know there are some avionics experts on here and was hoping to get an answer so we can do this tomorrow. 

Thanks!

 

Note:  Not talking about Power 1 and Power 2.  I take it that is for aircraft, like twins, with dual power sources.  This is just asking about pins 21/42 and 27/43.  

TwuEkA4.png?1

IIRC the GTX330 uses a HD (High Density) connector, so it is difficult / not possible to use 18 or 20Ga wire in the small pins.  There might also be a current limit per pin.  I've seen several installations where they join the two wires with a splice a few inches away from the connector.  Every splice introduces a new point of failure, especially if you don't use high quality splices and crimpers.  I used to like the AMP crimp splices, but my new favourite are the enviro splices.    Make sure you have the proper crimper, and a small butane heat gun.

https://www.edmo.com/product/D-436-0110/multi-wire-splice-red-d-436-0110

 

Aerodon

 

 

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2 hours ago, Aerodon said:

IIRC the GTX330 uses a HD (High Density) connector, so it is difficult / not possible to use 18 or 20Ga wire in the small pins.  There might also be a current limit per pin.  I've seen several installations where they join the two wires with a splice a few inches away from the connector.  Every splice introduces a new point of failure, especially if you don't use high quality splices and crimpers.  I used to like the AMP crimp splices, but my new favourite are the enviro splices.    Make sure you have the proper crimper, and a small butane heat gun.

https://www.edmo.com/product/D-436-0110/multi-wire-splice-red-d-436-0110

 

Aerodon

 

 

Aerodon,

You got it; It's a current limitation for 14V systems.  The newer version of the install manual, that I did not have, points that out.  I ended up doing exactly what you and JimB suggested and used the AMP crimp splices with the correct tool.  

 

3 hours ago, Warren said:

RS232 in is required from the 430.  Out is required if you use the “GNS” interface format, not required otherwise.

ARINC out transfers the TIS-A traffic to the 430.  You also need the TIS connect select (Pin 11, P1001 on the 430).

The Air/ground input is not ARINC but a discrete input on Pin 17.

Hope that helps.  Good luck.

Warren

 

Warren,

Thanks for confirming some of what I read.  Since the wires are already there on the 430W harness I bought, I am going to use both RS-232 wires since I will need to use the ADSB+ interface when I upgrade the 330 to ES.  I also think I am going to use the ARINC OUT from the 330ES to the 430 for TIS-A (with the TIS connect select hooked into Annunciata E per the Garmin 430W install manual) since it appears you can configure the 330 to Autostart your flight timer based on GPS provided speed data.   Might as well take advantage of whatever free traffic info I can get while in the Houston Bravo!  

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