What Ray is saying is what I’ve essentially done. I have an inline fuse right after the zone ports of the controller/extension boards, for each zone not the common. Amazon has the 5x20mm Fuse Holder Inline Screw Type (wire wire, black holder), those are what I’m using.
Go as low as you can with the fuse, I haven’t had a fuse blow yet on this set up so cant say at the moment (3 years?) about how well its working, but with my understanding tis the best option (Ray is confirming this in my mind). I have a few controllers set up more lazy like with a fuse on each common wire I have, and I’ve had burned out triacs with that set up….no blown fuses so that doesn’t seem to work.
Hope that helps,