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Posted by D Sherman [72.47.9.228] on Monday, September 19, 2011 at 19:28:25 :
In Reply to: OT but patriotic posted by mannyc [173.77.231.213] on Monday, September 19, 2011 at 18:47:00 :
From what I've seen of lighting, it doesn't always know the rules that it's supposed to follow. It'll hit a small tree right next to a big tree. It'll it in the bottom of a ravine rather than on the ridge nearby. It'll hit wood, masonry, or metal equally easy. The idea that metal "attracts" lighting is mostly a myth in my opinion. When there's lighting, there's usually rain, and anything that's wet is a good enough conductor as far as lightning is concerned.
If you think about it, the lighting has so much voltage behind it that it will easily arc 1000 feet through the air. With that kind if force, it doesn't really matter if the last few feet are aluminum, fiberglass, wood, or human flesh. It will _usually_ hit the highest thing in the area, and it's definitely "attracted" to pointy things (the things that would glow with St Elmo's fire) since they concentrate electric fields and make the air ionize easier.
The way I see it, it's rare for lightning to hit any particular thing, so I'd just take my chances and maybe put the pole far enough from the house and the power lines that if lightning does it it, it won't jump to the house wiring and do major damage. If you're really concerned and are in an area where you're pretty sure it'll get hit at some point, an aluminum pole would be best, since it will conduct the current without damage, whereas anything less conductive is liable to get blown to pieces like a tree getting hit. I do not think a metal pole is any more likely to "attract" lightning than any other material, though. As for grounding it, anything less than 2/0 copper attached to a ground rod deep enough to go into wet dirt is liable to be insufficient except to establish an arc in a desirable place before it vaporizes. It seems like the old Forest Service lookouts, which got hit all the time due to their locations, would usually run 1/0 or 2/0 solid copper from the peak of the roof, out along all 4 corners, and down to the legs of the tower to the ground, where they were tied together and then run out to multiple ground wires buried in the ground. For a flag pole, I'd probably just let it arc off the bottom of the pole to the ground wherever it wanted to go so long as there was nothing near by to catch fire.
Running electric wires inside the pole won't attract lightning at all, but if the pole got hit, it could send a big surge back into your house wiring. A 12 volt light system on the pole would help isolate the house wiring from any such surges. You can get big beefy surge suppressors that mount in your breaker box to help with that as well. Fuses and circuit breakers themselves are nothing to lighting, which will vaporize them and jump right over the gap like they were solid wires. Remember the lighting has already come clear down out of the sky. Nothing you put in its way will stop it once it hits the ground. All you can do is divert it away from fragile things by giving it an easier way to go. Even then it might have a mind of its own. Lightning can do strange things. I know of one case where lightning hit a tree that had a TV aerial on it. The lightning set up a standing wave in the coaxial cable that ran from the aerial to the house and melted the cable at every high-current node. The result was a pile of coax at the bottom of the tree all chopped up into pieces of equal length.