Edit post

Edit your reply below.

Post Body
Enter your post below.
It's not about "magnetic" charges - it's "static" electricity - electrical potential - voltage differences - between the cloud and ground. The voltage necessary to generate that huge (3 times hotter than the sun) arc discharge between cloud and ground is hundreds of thousands (or even millions) of volts. Power lines are indeed struck with some frequency - they are often higher than the surrounding conductors, and regardless of what charge the power company puts on them (which is by the way AC not DC so it's neither always positive nor always negative) they are close to ground compared to the charge the cloud is unleashing. They have spark-gap lightning arresters which arc over and take the brunt of the strike to ground (so most of it does not end up coming into everyone's house). Tracks might as well be ground. Whatever signal-activating voltage is there is low (24 volts or less is my guess - kids don't get electrocuted shorting tracks together with a length of wire to see the crossing signals go on) and is not relevant to the attractiveness of them as a ground-like target. They have 6" metal spikes driven into the dirty and wet (it's raining, remember) ties sitting on dirty and wet ballast sitting on ground. It may not exactly be zero ohms from the point of contact on the rail to earth, but the rails conduct and those spikes and ties up and down several hundred yards of the line make a pretty good ground. The lightning struck through a few thousand feet of air so that last few inches of ties and ballast looks pretty good as a conductor by comparison. Put a metal, 16-foot-high, steel-wheeled train on those rails and in open areas it's a juicy target. The anecdotes 2 or 3 others have posted here about lightning-struck engines in their shops within the last few months would seem to indicate it happens a bit more frequently than lottery winning. From NASA... "Typically, more than 2,000 thunderstorms are active throughout the world at a given moment, producing on the order of 100 flashes per second." Clouds are usually negative and the ground under them becomes positive in response so the strokes are "down" but a non-trivial minority of strokes are between positive cloud tops and correspondingly negative ground below. Two good references follow. The first is long but thorough - the 2nd of its 4 pages is particularly descriptive. The second reference is shorter if you don't have patience for the first. <hr noshade size="1"> [url]http://thunder.msfc.nasa.gov/primer/[/url] [url]http://www.lightningsafety.noaa.gov/science.htm[/url] <hr noshade size="1"> - Chuck Somerville
Tags (Optional)
Tags are keywords that get attached to your post. They are used to categorize your submission and make it easier to search for. To add tags to your post type a tag into the box below and click the "Add Tag" button.
Add Tag