Open Neutral- ( Not concerned with proper semantics or nomenclature to relate the story)
Had two occasions when rainwater or melting snow got into the crimped incoming neutral connection on residential service entrances, and froze which expanded the crimped connection and caused a loose connection.
One was missed by the utility co. on their first visit when they barely left the seat of their truck. I Told the home owner ( my bro-in-law) "call them back and tell them what I said to look for". He lost his well pump motor and a freezer with his deer meat. He saved the deer meat.
The second time, it was my buddy's two-story garage, same thing, the connection froze and expanded. He did not loose any machinery.
Had another occasion, a drunk driver coming home to his neighborhood hit a utility pole. And of course according to Murphy's law it is always the most expensive pole to hit, that is, the one with the cans on it.
The surge affected a few houses. One house, with white siding had a vertical burn mark where the telephone and cable TV wires used to be. The township electrical inspector was also a cop, and he confirmed the incident when he inspected my work. How he was a cop and an electrical inspector is another interesting story. ( Air National Guard Civil Engineers )
My customer across from the white house lost his service and had several problems. This is why a good trouble shooter has to double as a detective. The ground connections to the water pipes burnt open. The customer had more than one ground to copper pipe, and it could have easily been overlooked. The, clothes dryer, dishwasher, a TV or two, the cordless phone chargers and other items were ruined.
Of course when I installed a new service, I had to bring everything else associated with the service, panel and grounding up to code.. including at the time, two ground rods.
I am also an HVAC building engineer an in-house electrician. For my own pleasure I enrolled in a two semester HVACR class.
The question asked earlier; could a surge have affected the condenser unit on a split system. Don't rule out a surge passing through any metal connection. The copper lines to the unit are attached to metal of the evaporator fan coil which is most likely located in the heater/furnace. The A coil sits in a metal box which has a single pole circuit to the heater with a ground and neutral. There's one or more capacitors and control elements out in the condenser unit, The wires between the thermostat and control boards are what, #18 solid copper, may be brittle from exposure to outside moisture and degraded, takes little effort to bend back and forth a few times and break.
Could the seal-tight used to connect the outdoor safety switch to the condenser steel cabinet have a metal core. Could there be 10-2 Romex from the main panel to the safety switch for the condenser that has a "ground wire" bonded to the safety switch if it's metallic. A utility line surge just like a lightening hit can have some amazing results that can be the topic of conversation at coffee breaks.
Early on in trouble shooting lessons a wise teacher said to us students, "eliminate the obvious, go from simple to complex"
