On Friday, May 20, 2016 at 12:51:45 PM UTC-5, westom wrote:
On Friday, May 20, 2016 at 8:30:13 AM UTC-4, Uncle Monster wrote:
The house is 100 yards from the very highest point on the mountain. The long metal duct in the basement of the house acts as an antenna to pick up the EMP or static pulse from the lightning strike.

Lightning strikes only 50 feet from a long wire antenna. That EMP to a device intended to maximize EMP effects is easily removed by a milliamp current device - one an NE-2 neon glow light. Same bulb also found in lighted wall switches. EMP would not create that arcing. Something more robust created it - such as currents in earth that traveled two miles into the house and probably more miles after the house.

Those current are why both overhead and underground wires must have that same service entrance protection. As even addressed by Mil Std 419.

Same problem is why mines must be carefully earthed. In one case, a lightning strike direct to earth some distance from a mine caused wires inside the mine to arc. Arcing caused a small explosion. Even underground mines must have effective and properly earthed protection from lightning.

It's been years since I was back there but the power is coming in from overhead and now that I think about it, the furnace and metal ductwork could have been grounded to the incoming power line and the arc could have been caused by a difference in potential from the electrical system ground and the steel support poles embedded in the concrete slab and its metal reinforcement grid. I don't recall if the reinforcement was rebar or screen wire. I just remember being in the basement involved in some evil mad scientist stuff when I'd hear a loud crack followed seconds later by thunder. It's been more than 40 years since I was back on the family farm in that basement so I can't investigate with old experienced eyes. ^_^

[8~{} Uncle Potential Monster