We had a lightning strike nearby yesterday that looks to have come inside our facility via a feeder circuit that goes outdoors underground to our facility's gate.
Perhaps there was a "move" of the earth-level relative to the neutral line. I have no idea how neutral-line to earth potential is handled in us, but here in austria we use a so called "nullung". That means that the earth-ground potential line of the building (which includes also the lightning conductor) is connected to the neutral power line where it enters the building, keeping this potential-difference low. Theres also a potential between earth ground and the neutral-phase of the online-ups. The ethernet-cables; utp or stp? pannels correctly earthed? Perhaps a electrician should check the earthing. Also all copper lines that enter the building should be protected by lightning protectors. Kind regards, Ingo Flaschberger