Finally, I can put "THE END" on the great electric arc story, the one that caused the SPOCS garage node to go offline for a few days, because the Modicon PLC at node 11 was complaining of random CRC errors.
It turns out that not only did the zap take out the main RS-232 to RS-485 converter, but it also damaged the communication cable leading from the Penguin farm to the garage. I finally ran a new cable, and everything is back to normal.
Finally! Now I can get back to wiring new SPOCS inputs to accommodate our new heating & air conditioning system. I got the new temperature sensor put in the day the air conditioning was installed. As you can see, the heat pump system keeps pretty tight control over the house temperature. My installer said that a deviation of 0.6 degrees F. was OK, and that's about what the system has been doing.
The control system for the furnace / heat pump is 24 volts AC. I have to wire several relays to connect to SPOCS Optomux-clone inputs, so we can monitor the system. That's next up on the workbench.