@ninjago - Yes, you’ll need either the isolator or a relay (cheaper). The relay will cost about $15 (including shipping), or less, here is an example -> http://www.ebay.com/itm/MAGNECRAFT-92S11A22D-24A-Enclosed-Power-Relay-30A-24VAC-DPDT-/221561305796?hash=item3396153ac4:g:ZD4AAOSw2gxYtaaX
The one Gene sourced in the linked post is ~$7 and has a light when one side is active.
You don’t want to connect two electrical sourcing (i.e. Rachios) devices together, the current flow can get strange.