G3x OAT probe grounding question ?

The instructions say to ground the ring terminal against the bare clean Alclad wing skin interior. I have been running ALL grounds back to the battery bus (tabs) for good practice (No airframe grounds),
My question is, if I run a ground wire to the battery bus, in addition to ring terminal under the probe, will that create a ground loop ?

The airframe (aluminum) is a fine ground/return path. There's no need to run a matching ground wire from the load to the battery (-) in an aluminum airframe.

I would ensure continuity (i.e. very low resistance.... .01 Ohm or less) across major assemblies, e.g. wing to fuselage, engine mount to firewall, etc. Use a grounding strap or similar to connect these items.

It is a resistive temp probe. So there will be no noise so a ground loop is not possible.

Pilot2512 question ?

Please educate me. Why are there three wires plus what appears to be a shield grounded at both ends ( wing skin and Db connector ??

The 3 wires are +, - (gnd) and a sense wire. The signal that is being measured is very small and that is why they are shielded. Garmin likes to ground both ends of the shield unless it is an audio signal.

Larry DeCamp said:

The instructions say to ground the ring terminal against the bare clean Alclad wing skin interior. I have been running ALL grounds back to the battery bus (tabs) for good practice (No airframe grounds),
My question is, if I run a ground wire to the battery bus, in addition to ring terminal under the probe, will that create a ground loop ?

Click to expand...

There is no need. That ring terminal goes to the cable shield, which is likely already grounded to the common ground plane on the other side of teh cable. THey just wan't the shield grounded on both sides. This is no different than ground the shield on the canbus cable locally at each termination point.

Larry

Larry DeCamp said:

Please educate me. Why are there three wires plus what appears to be a shield grounded at both ends ( wing skin and Db connector ??

Click to expand...

It is a two wire RTD thermistor and industry best practice is to use 2, paralleled wires in the connection of the + side of the thermistor and unit. As above, it is a shielded cable and they spec'd it to be grounded on both sides. Yes, your wing skin is part of your airframe ground.

The probe chassis needs to be electrically bonded to the airframe and is the point of the instructions calling for clean contact with the skin. The built-in bonding jumper is a belts and suspenders check to make sure there is good bonding, which also includes the shielding of the probe lead (already done internally). The power ground is also obtained through the probe body bonding to the skin so there isn't really an option to run the ground separately and adding another wire going back to a ground behind the panel will only add weight and is unnecessary. If the probe is mounted in composite structure like a wing tip an extra bonding wire has to be added to the probe chassis that runs to the nearest local grounding point. The actual wires included in the 3-conductor shielded OAT lead going back to the LRU are power, signal Hi and signal LO.