Mike:
The whole thing is acting like a transformer in a sence.... The current flowing in the lines overhead is creating a magnetic field around each of the lines ( in this case a very strong one).. The magnetic field in turn is now generating (inducing) a voltage in the metal work of the tent poles and lighting and power cords and what ever was present at the time...
There is no electrical "leakage", its just being in the wrong place period..
Personally I am amazed that Twincitysparky was able to draw a 1/2 arc off one of the poles.. What was I told once,roughly 33,000 volts jumps something like a 1" air gap???? ( depending on conditions) So that would equal about 16,500V present at the poles, albeit the current would be so minimal it would be very uncomfortable to be in contact with, yet still VERY unsafe..
A.D
