The problem, of course, is that we'll never find out whether all that copper cable helped the 911 tower or not. So many lightning strikes leave no evidence at all; only the rare high-current stroke (are they all that rare?) sets the grass on fire or bends the anchor of the ship.
When I first started working in our artificial lightning lab I was shocked to find that the conductors used there were #20 bare tinned copper wire. You could barely see the stuff, which wasn't handy when you're carrying a ladder. It was explained to me that though the currents were exceedingly high, they didn't last long enough to heat anything up.
The ground resistance of the system is low, and that's fine, but I don't believe that it matters as much as all that. It's the high-frequency AC impedance to earth that matters, and even with that it's only a guess as to what path a stroke might follow. The important thing is that the vulnerable parts of the system are well protected.
Ground resistance is very important in the design of electric power system facilities, but lightning currents are far less predictable, alas. But for all that, I strongly approve of the robust grounding and bonding used here.
One thing we learned in lots of lab research on the subject is that lightning current that goes into the ground doesn't spread out in an orderly manner like the hemispherical distributions shown in much of the literature. In fact, it goes along discrete paths that look remarkably like the paths that it takes in air.
Reply to this comment | 
