Can 2 Rachio controllers share a single common wire?

[Gene]

Yes, sharing a single wire should not be an issue, as long as you share only a single wire (not a master valve as well, etc).

More discussion on this here:

Multiple Rachio Controllers with Shared Command and Master Valve

Perhaps it would be helpful to think of isolation in terms of the bird on a power wire. As long as the bird is touching only one wire, it is safe no matter the voltage within the wire itself. Sharing a single wire (commons) between multiple controllers, is like multiple birds sitting on the same wire. As long as birds are leaving each-other alone, we can have peace and quiet. Isolating commons, such as with your original configuration is like shooing one of the birds away when the second one ne…