lightning strike

[hastime]

I was called to an emergency job where lightning hit a house. Sure enough ligtning had hit a metal vent in the attic of the home and started on fire. The fire was contained to the small area of the vent. They lost all the phones, TVs, computers and GFCI receptacles and the next door neighbor lost his GFCIs and phones as well. They have underground service.

I am a little confused on how the house electrical as well as the neighbors electrical was affected. There were some electrical home runs in the attic about 8 to 10 feet from where the lightning hit. I know that the lightning has to go to ground but there was nothing up there except wood. No wiring was damaged but equipment. Can someone help me understand some possibilities on how this lightning strike was able to cause all of these problems with no apparent grounding source even near the damage. Like I said it hit a metal roof vent.

thanks, Don Hastings

 

[LarryFine]

Re: lightning strike

There's a lot more to lightning than DC or 60Hz. Sparks create an enormous amount of RF energy, which can induce electricity in nearby wiring and other metal parts, and lightning is the ultimate spark.

 

[bphgravity]

Re: lightning strike

My guess would be that the vent was not the direct strike. It was probably hit by a flash-over event from a nearby ground strike that entered the service or utility entrance.

 

[charlie b]

Re: lightning strike

Originally posted by hastime: I know that the lightning has to go to ground but there was nothing up there except wood.

What makes you think that wood is not a conductor? Granted, it is not a really good conductor, and will not carry much current without a really strong push. But lightning is a very relentless pusher of electrons, and can make them move through almost anything.

As to the damage in the neighbor's house, it is not a surprise to me. Regrettable, but not a surprise. Lightning is a sudden and rapid event, and can cause voltage spikes anywhere near where it hits. My guess is that, for perhaps a few milliseconds, the voltage of planet Earth in the vicinity of the strike went very high, and then quickly returned to normal.

 

[cripple]

Re: lightning strike

What was the vent for, if it was for the hot water heater or the furnace, and the cold water pipe was grounded to the service, would it not provide a path to ground?
As for the neighbor, if fed form the same utility transformer, would not have thee grounding electrodes on the same system? As lightning current flow in the ground (earth) depending on each of the grounding electrode connection the ground (earth), would you not have a potential to ground between on each system? The insulation on the equipment damaged may not withstand the potential generated from the lightning strike.

 

[celtic]

Re: lightning strike

Lightning strikes homes in Wharton and Mine Hills (07/25/05) MORRIS COUNTY, NJ

 

[charlie tuna]

Re: lightning strike

look for "tracking" on metallic raceways -- looks kind if like a charcoal pencil line and usually runs around the path --- possibly came in on the cable system -- then jumped around the attic attacking anything metallic. this tracking will wipe off if you touch it. i have seen this type of strike many times --- wipes out anything electronic once it gets into the electrical power systems grounding surface. many times you can trace the tracking and then determine where it jumps to another surface??

 

[jimwalker]

Re: lightning strike

Lightning follows it's own rules.Having first been a T V repairman and then electrician i have seen plenty of damage from it.It is able to go right thru a window and circle around the house till it finds ground.Recently seen a house where proof was there that lightning went thru upstairs window and blew up the room.Shattered the framing.2inch hole was in the window.The voltage is in the thousands and can use wood or anything else to go thru.Stop and think ,it just went thru a great insulator AIR