Hello can anyone explain me the example given in this section?
In particular the second figure and why there are different values of 'n' depending on the distance from middle point.
I have used the rolling ball method, but not this. I looked for some science but ended up finding history for lightning protection starting with Franklin. History showed if it worked, great, otherwise make a change. In this case, the result is for determing the distance for sideflash. In an NFPA code write up, there was discussion that n=1 would work as its almost impossible to have other configurations. The idea is that distance and the number of down leads to ground can change the sideflash 'D'. Maybe someone else has better information.
Dear James thanks for your comment!
I wonder why the value of 'n' changes from 2.25 to 1 @ 60 ft from the point of interconnection along the 150 ft overhead wire AND from 2.25 to 1.5 @ 25 ft from the point of interconnection along the 80 ft overhead wire as shown in picture A.220.127.116.11 (b)
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The value of “n” relates to current division of the lightning impulse when multiple conductors are involved. This has been codified in 18.104.22.168 in the description of “n”. At the point of interconnection of the overhead wires there are four down conductors located within 100 feett of that point, leading to a value of n = 2.25. When you move the point of consideration along the 150-foot overhead wire, there will be a point 26 feet from the node where the opposite mast will be greater than 100 feet away so the value of n will be reduced to 1.5. At a point close to a mast on this span, the value of n will be reduced to 1 because there are no other down conductors within 100 feet.
Thanks for your comment Mitchell!
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