I am wondering what would be the correct location to connect the unconnected green ground wire in main panel next to meter. The detached garage has it's own ground rod. It is being fed by the double pole 50 amp breaker in main panel next to meter. I attached photos. The bare aluminum cable in main connects to ground bus bar in breaker box located inside house. The ground rod under meter connects to inside meter box only.
The hanging #6 green wire and 3 other black #6 wires run 60ft underground in conduit to detached garage sub panel. Two black #6 are on each pole of double 50 amp breaker and other black #6 is on neutral bar of main box next to meter.
Best Answer
Fit a ground bar to the main panel, land it there
While, since you're working in a main panel here, you could commingle neutrals and grounds by landing your new ground wire on one of the neutral bars, it's cleaner to avoid that altogether and install a separate ground bar into the main panel instead for the ground wires. Since you have a Square-D main panel, the correct part for your situation is a PK12GTA or PK15GTA -- you should be able to find it at a local electrical supply house or order it online for about $10. Simply mount it to the main panel's cabinet in the holes provided, with the meter pulled for the duration (there should be a set top left or top right -- if not, the install instructions give guidance on drilling a set of mounting holes), then attach the ground wire to the newly fitted ground bar. Once that's done, have the electric company turn the power back on, and enjoy your new subpanel!
(The previous installer committed a bit of a no-no by using a black wire for a neutral and phase-taping it instead of using a white wire, but that can be rectified down the road if it ever becomes an issue. I would suggest phase taping it white at this point, at a minimum, to avoid needless confusion due to the previous installer's non-standard phase-taping scheme.)