Only ONE little drawback...

In my last post, I was extolling the great things about whole-house air conditioning.  It's been pretty good, with one exception.
I was wiring a new plug for power for the condensate pump.  We had it plugged into an extension cord, temporarily.  I was installing a real wall-mounted duplex plug to supply power to the pump.  In the process of connecting the plug - I didn't want to turn off power to the lab, so the wiring was live - I accidentally shorted the "hot" lead to ground.  It was only for a moment, and drew a nice spark.  It didn't even blow the breaker.
BUT - SPOCS immediately started telling me that some communications were down.  Somehow, that arc caused the main RS-232 to RS-485 communications converter to give out.  Even though everything is powered through UPSs or at least, surge-protector electrical plug strips.  The bad part came when I replaced the converter - and discovered that the spare was bad, also!  Fortunately, I have several of them.
Node 11 - on slots 2-4, is still occasionally complaining of occasional communication failures.  I have checked every connection in the network.  I swapped the PLC, which is living in slots 2-4, with another one.  No change.  All other communications are working fine.  Grrr.  I will find and fix this.  It is taking away from getting the new inputs from the furnace / heat pump system.