I have an OSPi (1.43+). I realize the OP has different hardware but I think most of this would apply. Had an issue with storm transients and some misconnection of an expander board that fried the on board regulator (if I recall correctly – it’s been a LONG time). I elected to remove the damaged regulator and feed the board with an independent 5V regulator so I could feed 12V through the unused ethernet conductors from a supply at the router using a UPS to avoid SD card corruption for short power drops. Not to get too long winded but that’s some back story. I added an in line fuse holder to the 24VAC input- ugly but it works and the fuse is easily replaced. I did build and bench test a solid state AC current limiter that is very simple – just a couple common transistors, some diodes and resistors. My plan was to install it in place of the fuse or possibly in addition to it. Since the fuse only powers the zones now I could easily put this in place of the fuse and only limit current to the zone circuits. Even thought of sensing the current limit and reporting it somehow. I didn’t have further issues so never put the circuit in place but should dig out the details and post it I suppose. My zone expanders have 2.2 ohm resistors in series with the triacs IIRC which just burn up in the case of a short. They burn the PCB making it hard to repair.