HVAC controller grounding by code.

[qcroanoke]

Have a HVAC redundant controller with a installation manual that states, " A reliable earth ground must be connected in addition to any grounding from conduit."
If I use the HVAC unit's equipment ground for this do I have to pull the same size ground that the unit has to the controller or can I downsize it to #12? Any unit we wire is usually a #10 ground.
The controller is all 24 v.a.c. No line voltage is present.
Also, If we run a conduit from a nearby receptacle to the controller and pull only a ground wire through
it are we creating a potential problem? I have heard it's something that you don't want to do.
Thanks!

 

[S'mise]

250.122 says In no case shall EGC be required to be larger than the circuit conductors supplying the equipment. So if your supply (in that panel)is #18 thats all you need.

I would not get too worried about tying in with your #10 in the other panel. This is just for bonding. Just drill and tap a hole in the backplate to bond it.