Lighting Strike

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Minuteman

Minuteman

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The Sooner Nation
The restoration GC I work for sent me to a 1 1/2 year old house out in the country that was stuck by lighting (2002 cycle). Nice house about, 3000 - 3500 ft/2 with a big burn spot in the roof ridge. Several of the wood members damaged. Drywall nails backed out (not screws?). Computer and older big screen TV zapped. But the ONLY electrical system damage was to one dimmer switch on the same ungrounded as the computer.

Question: Did the Uffer (CEE) and supplemental ground rod make any difference on how well the lighting was dissipated?
 
Minuteman said:
Question: Did the Uffer (CEE) and supplemental ground rod make any difference on how well the lighting was dissipated?
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LIGHTNING

Maybe yes, maybe no. The grounding of the electrical system will not protect against direct strikes to the building or structure. It may assist in diverting surge currents into the Earth in the event the service entrance is struck or induced by a near by lightning strike that enters via the service entrance or from the earth through the grounding electrode system.

It?s possible that appropriate TVSS at the service and at the outlets of the utilization equipment would have been effective in protecting the equipment. The grounding of the system in this particular occasion likely played no significant role.
 
Lightning bolts also can be of varying intensity. That also needs to be factored in, and in my opinion makes the study of the effectiveness of the grounding system at a building a mystical science. In order to measure the true effectiveness of any system, we would need consistancy in the energy level and proximity of the strikes.
 
Minuteman said:
... Computer and older big screen TV zapped. But the ONLY electrical system damage was to one dimmer switch on the same ungrounded [branch] as the computer ...
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This seems to reinforce the value of good grounding/bonding; if everything experiences an equal rise in potential ... damage is minimized.
 
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Originally Posted by Minuteman said:
... Computer and older big screen TV zapped. But the ONLY electrical system damage was to one dimmer switch on the same ungrounded [branch] as the computer ...
Click to expand...

Originall Posted by NoVa Comms Power said:
This seems to reinforce the value of good grounding/bonding; if everything experiences an equal rise in potential ... damage is minimized
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My mistake, I was refering to a "hot" circuit, called an unground conductor.
 
"the ONLY electrical system damage was to one dimmer switch on the same ungrounded as the computer."

Are you sure, that was the only electrical damage, did you breakdown test all the cables in the walls, for insulation breakdown!
 
I would say the grounding system did help, by "directing" the bolt to ground (you can't really contain it with a system this light) and by reducing the voltage spike on the rest of the equip.

I like a 2 pronged tvss approach- an in panel tvss (hi energy, moderate clamping voltage) with short leads, and a good plug strip (lower energy, but protected by it's own breaker and a lower clamping voltage) nearest to protected device, with LV signal protection. Gotta have good bonding of all systems, and I would go to great lengths to make all the entries in the same physical location.
 
satcom said:
"the ONLY electrical system damage was to one dimmer switch on the same ungrounded as the computer."

Are you sure, that was the only electrical damage, did you breakdown test all the cables in the walls, for insulation breakdown!
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I will be at the place Friday, to install an outlet for their new flat screen, so I guess I could Meg Out the wires.

FWIW, I do know how to spell lightning, I'm just testing Brian :D
 
You would be supprised, how many near strike jobs, where the cables in the walls, looked like a spent firecracker, and the circuits were all working, after a few of them, we started to meg all the cables, because most of the time the owner will ask, is it safe, by megging the cables, and getting good insulation results, does not mean the cable is not damaged, we tested some and they measured good. then the wall was open and the cable was damaged, but at least it passed the breakdown test.
 
Had a situation like this recently. The lightening hit the house at the corner of the rain gutter, traveled thru the gutter and out the other end where it blew a hole in the gutter. The TV and computer in the basement were fried. As it turned out this house had old AC cable wiring with two prong receptacles. Yes, the TV and computer weren't grounded and to make matters worse the receptacle was reverse wired. Didn't have a megger but I changed out the receptacle. HO didn't want to go for lightening and surge protection at the panel. Go figure !!!
 
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