Can 2 Rachio controllers share a single common wire?

Unfortunately, my yard has more than 16 watering zones. I am using a Rachio 3 to support 16 of those zones. I also have a Rachio 2 that I would like to use for the remaining zones. The two controllers are co-located with each other inside the house and all of the valves are inside multiple valve boxes spread around the whole yard. Each controller has its own AC power supply. Each zone has its own dedicated wire, and there is a single “yard common” wire that is routed to every valve box and therefore each valve. The question is can my single “yard common” wire be connected to the Common terminals of both controllers? I am somewhat concerned because I am measuring somewhere between 2 and 3 volts AC between those common terminals. Is this a problem? I’d like to avoid having to run a separate/unique common wire for all of the zones connected to the second controller. If this is a problem, is there a solution that does not require having to run a new wire? Thanks.

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).

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