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Garmin Heated Pitot wiring

JDBoston

Well Known Member
I have seen a few threads on this, but I still have a question.

I am going to put a Gretz mast in place but plan on closing up the wings over the next week. For a GAP26 Garmin Heated pitot it looks like I have to run 12 AWG wire (or maybe 14) from the mast to somewhere. I would have hoped that they had thought already about this with the wiring bundles but it is not the case.

Does anyone have a description or picture of what they actually did? Is it two wires, and if so where do they terminate? I would assume that is somewhere in the panel so I need to run enough to get to the panel.


Thanks.
 
Well yes it needs to be pretty large guage wire. One should go to your Pitot Heat switch and the other should go to your grounding block which is usually mounted to the firewall.
 
I didn't author this, I copied it from somewhere about one week ago. I pass it along for your perusal.

For pitot heat, you need a separate switch & fuse or circuit breaker along with appropriate wiring for appropriate length & amount of load carried--per advisory circular AC 43.13-1B, chapter 11, section 5. Probe heat requires over 7 amps of power. Use shielded wire to minimize interference with other instrumentation, & route wiring such, that the risk of mechanical damage, and /or damage caused by fluids, vapors, or sources of heat is minimized.

2> Follow installation manual & use AC 43 as discussed in the manual to complete installation.

Again, don't mean to insult your intelligence, I just pass this along in case any of it helps.
 
G3X insatlltion of Pitot - Wiring

You should down load a copy of the G3X installation manual and look at section 4 page 4-2.

1. AIRCRAFT POWER WIRING TO PROBE SHOULD BE MINIMUM 14 AWG UP TO 12 FT, 12
AWG FROM 13 TO 20 FT, AND 10 AWG FROM 21 TO 30 FT. (AC 43.13-1B)
 
On my 10, I ran the power wire from the VPX under the panel out to the pitot mast. It was either 10 or 12 gauge. I ran the ground to a local grounding block that I installed on the last rib of the wing, which is easily accessible with the wingtip off. No issues, no audio noise. I'm also grounding the LED landing lights to the same block, but Nav/strobe lights get a dedicated ground run all the way back to the main grounding block under the panel.
 
with the Dynon/AFS AHRS/magnetometer mounted in the same wing as the heated pitot on the 14, has anyone used shielded wire for the pitot power, like the note above stipulates? Would twisting the non-shielded wires help?
 
Pitot Wire

Garmin recomends sheilding due to the very high current, both on red and black. I used a 2 conductor shieldied wire back to the VPX
 
The shielding typically used on shielded cables is not very effective for magnetic fields. However, running the ground return right next to the power (twisted even better) wire is very effective at reducing the magnetic field radiated.
 
I worried over this exhaustively about a month ago.

The heater control boxes are grounded so when you mount them they will ground to the wing. If you run a separate ground wire back to the battery you will still have current in the wing and in the wire both. This is a feature of the way the controller MOSFET is mounted to the controller box as a heat sink. The wing is likely a larger return path than the wire so a ground wire might not even carry much current in it.

I ran a 12Ga wire in the large bundle out to the pitot location for the 14V, and will be grounding the controller to a bolt in the wing. With a metal wing there isn't a reason to have a separate wire back to the battery. Many people have done this without concern, radio problems, or ??? and it it is recommended to do so in the Nuckoll's literature both online and his book.

My biggest worry is that the current will mess up the magnetometer if the ADAHRS is installed in the wing the way the plans look like is intended. I thought that if I ran both supply and ground wires that there would be a balanced current that would not generate much magnetic field but once I found the controller box was grounded this consideration evaporated.

So I will plan on having a magnetometer somewhere else if this really becomes a concern.

One other thing to note in the Garmin heated pitot. There are two hot and two ground wires. This is because it is sold for both 14V and 28V applications. The wires are parallel for 14V and series for 28V; you don't have to run them all back to the battery.
 
It would be simple to isolate the controller box from the wing and run all grounds back to the panel twisted with the power cable. I'll see if I can get Dynon's opinion on the optimum method
 
There are a few basics that bear thinking about here,

- Shielded cable is used to prevent RF interference and has no influence on magnetic interference (woven iron shielding is required - heavy and not that efficient).
- Taking a ground wire back to a single point is to avoid 'ground loops' and interference on the audio system - typically from AC and high frequency switched devices (doesn't sound like a heated pitot to me).
- Local grounds are used to save weight - sounds useful when a 14 or 12g conductor is required.
- Wire gauge depends if the conductor is bundled or not and the length of the conductor (potential volts drop), use the thinnest conductor to save weight.
- Weight saving in all aspects of the build is key to achieving good overall aircraft performance (in any aircraft).

Use a single conductor of adequate thickness for the length and ground to a wing rib. Position a magnetometer far enough away from the pitot that it is not affected (AP servo same side as pitot with magnetometer in the opposite wing or rear fuselage). I believe Garmin install manual shows magnetometer under the HS fairing? Shielded cable and running a ground back to the forest of tabs is just heavy for no performance benefit.

Pete

PS my (biased) opinion is Safeair 1 produce a better pitot mast than Gretz
 
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to follow up: talked to Dynon and they said both power and ground wires should definitely both be run back to the panel (no local ground). They stated that their controller case is not grounded, (so I guess the current in the ground wire should match that in the power lead). I'll check the case ground to make sure after I get the wiring hooked up.

So I plan on twisting the black and red (14ga) wires together with the white 18ga wire and running them separately (not in a bundle) back to the panel, keeping as far as possible from the AHRS/magnetometer.
 
I guarantee you that the controller box is grounded. 0 ohms between the black ground wire and the box. It is so by design as the mosfet that controls the heater current is heat sinked to the box, and that part of the mosfet is ground.

The controller box ground as the main ground is not adequate, as you would not want to ground the whole board via the mosfet heat sink, hence the separate wire. But grounded it is nonetheless.
 
Just to close the loop on my side, I am going with running two wires back to the panel (three if you include the signal wire for the regulator) vs grounding locally.

I asked Vans and they stated that they have no current options, and that in the future there may be some sort of guidance with the avionics packages but those will be through vendors vs shipped via vans.

Garmin told me that they recommend running a ground wire back to the main panel.

Thanks for all the advice.
 
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