The problem with the pitot heat controller is that the chassis itself is grounded, and this is the same ground as the line that normally bolts to the wing structure. This is done for a few reasons, and is part of the way the MOSFET in the system is grounded to carry the heater current and the heat sink design to the case. So I don't think that it is possible to completely return the ground current via the ground lead. Most might go that way but a very significant portion will return via the chassis mount. The controller case should not be isolated from the mount with fiber washers; it is designed to be grounded. The ground return line exists to ensure there is a good ground return separate from the chassis mounting, and because the resistance to ground via the case is sometimes a little higher because the mounting hardware isn't as reliable for electrical connections. But I haven't checked the differences because I haven't cracked the case to see. A lot of circuits like this have a ground lead on the same connection inside that bolts to the case - the screw that holds the MOSFET down.
I think that putting a larger diameter wire cuts down on impedance as well as reducing overall resistance but is probably a trivial difference for the magnetic field of the power feed.
If it wasn't for the proximity to the magnetometer it would be moot. Nuckoll's book says wire to the chassis don't worry about it and that is correct in general.
Ser 104142, RV-14A
Ready to gas it up!
Last edited by JDA_BTR : 09-04-2017 at 09:57 PM.