I explained to googles AI that I had two lightning rods on a metal roof and a heavy braid that goes across the roof connecting them both to two ground rods on opposite sides of the cabin (separate from the panel ground on the adjacent side). I then told it that my tower is not cemented in and that it is just 20 feet of tower bolted to the cabin. I explained that I had a ground cable running from the tower leg to the heavy braid and that the lightning arrestor is also attached to the braid via a clamp about 10 inches above the ground.
It said that was terrible and extremely dangerous. I wasn't expecting that. It said I need to give the lightning arrestor its own cable down to the common point on the grounding rod because even that little 10 inches of braid from the rod up to the lightning arrestor represents a lot of inductance at RF (which lightning is composed of) and that I would have a situation where about 20kv would come back through my coax, into my radio, and then hunt down household ground from there.
When I said that the coax shield was bonded to the tower at the feedpoint and mentioned the tower physically touches the metal roof, it went into full panic mode. It told me that it was going to flash through my metal roofing and start a fire and that the arrestor is doing nothing in that case since the location it is clamped to will be at a similar potential as what comes down the coax and therefore have nowhere to go but down the center conductor.
Just when I think I have it all fairly well grounded, AI comes along and says its all wrong. I guess I need to dig down to the top of the rod and add a dedicated cable for the tower leg and for the arrestor. I had no idea that something like 10 inches of shared ground could be an issue.
edit: yea i better make sure that house ground ties in with the roof ground too. If the lightning brings the ground up several thousand volts at the roof rods and not the mains rod, there's an opportunity for the arc to jump from device to device. I guess I have work to do.
It said that was terrible and extremely dangerous. I wasn't expecting that. It said I need to give the lightning arrestor its own cable down to the common point on the grounding rod because even that little 10 inches of braid from the rod up to the lightning arrestor represents a lot of inductance at RF (which lightning is composed of) and that I would have a situation where about 20kv would come back through my coax, into my radio, and then hunt down household ground from there.
When I said that the coax shield was bonded to the tower at the feedpoint and mentioned the tower physically touches the metal roof, it went into full panic mode. It told me that it was going to flash through my metal roofing and start a fire and that the arrestor is doing nothing in that case since the location it is clamped to will be at a similar potential as what comes down the coax and therefore have nowhere to go but down the center conductor.
Just when I think I have it all fairly well grounded, AI comes along and says its all wrong. I guess I need to dig down to the top of the rod and add a dedicated cable for the tower leg and for the arrestor. I had no idea that something like 10 inches of shared ground could be an issue.
edit: yea i better make sure that house ground ties in with the roof ground too. If the lightning brings the ground up several thousand volts at the roof rods and not the mains rod, there's an opportunity for the arc to jump from device to device. I guess I have work to do.
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