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I was visiting a customer site who had their equipment fried by lightning and granted they forgot to install surge protection, so that's most likely what did it, however I also noticed they had the transceiver electronics mounted to the outside of the tower and the cable (Ethernet/POE) was routed on the outside of the tower from top to bottom. Since the tower is of course made out of metal I was thinking all the energy of the lightning would go down on the outside because of the skin effect. Looking at pictures of antenna towers I see it done both ways so I'm not sure how significant the effect would be and if I should tell them to move the whole thing to the inside (other than the antenna itself) or if they shouldn't worry about it once surge protection is in place. Any thoughts?

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Without exceptional grounding of each leg of the tower with heavy straps and grounding rods and an unshielded 4ga ground wire from the antennas the Electromagnetically induced surges are severe on any conductor inside or out.

Under direct strikes to the tower/line, the voltage rises quickly at the contact point. Current and voltage propagate in the form of traveling waves in both directions. If the voltage exceeds the line-to-ground voltage of system insulation, it can produce an insulation flashover and a surge.

The primary purpose of ground wires is to shield conductors, capturing the lightning strikes. The degree of protection depends on the location of the ground wires relative to the conductors.

When lightning current travels in both directions along the ground wire and tower, it induces traveling waves in the conductors. When a traveling wave reaches the ground through a high inductance tower and the footing resistance is high, a flashover may occur. Having the signal conducters inside the tower is not going to prevent the damage. Besides the Antennas being disconnected from equipment to prevent the path of current the grounding prevents the flashover

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  • $\begingroup$ I didn't even consider the induced current so that is a good point and you're right it won't matter inside or out. Maybe what this means is that on the inside it is only the induced current which may or may not cause damage but on the outside it is not only the induced current but can also be the actual lightning current or part thereof, would you agree? I did notice heavy grounding wires on each leg, I'd say they were about 0.4 inches thick. At the very least if it's mounted on the inside there probably wouldn't be a direct strike which could easily happen on the outside. $\endgroup$
    – pgibbons
    Jul 25, 2022 at 11:51
  • $\begingroup$ The grounding will bring the near field current away from the inside conductors as well as prevent the flashover that utterly destroys the conductors and any connected equipment. You will notice with the mains power above ground both phases have aground with them. The ground prevents tung destruction. Lenzes law is the whole rule book on this. I believe the frequency of tung strikes are 30mhz if I recall. It's the return strike if the grounding is not substantial enough. 1/2" wire will take a substantial amount of current if each leg is grounded. The feed thru needs grounding too. $\endgroup$ Jul 27, 2022 at 16:05

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