Have you read about the Carrington event? The EM energy was so intense that it caused fires from telegraph transmission lines to telegraph offices. Sure weren't any elecric power grids back in 1859. Apply this to any form of wiring, and realize what the impact will be to general electronics, their hardware, software, and associated controls. If you are an engineer, (as I), then you will realize how this will impact any form of manufacturing that employs computer controls.
“If you are an engineer, (as I), then you will realize how this will impact any form of manufacturing that employs computer controls.”
For manufacturing systems, Small dimensions = small impact from a solar flare
Twisted pairs (you’d better be doing this anyway) = small impact
You are right, any DC telegraph systems will be seriously impacted in a Carrington event.