KA3SGM
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join:2006-01-17
West Chester, PA
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 ·Verizon FIOS
| reply to burner50
Re: The Science of Effective Grounding...
said by burner50  :Guess i never consulted the NEC... never heard of that either... We put in a similar field at my last job except we used 24 rods, but this was for a freestanding structure not an aerial antenna. Edit: A 15x15 structure with about 20 million worth of electronic equipment I think the NEC intent is that a 6 foot spacing between ground rods that are bonded together comprises two separate ground points.
Anything closer than 6 foot is obviously better than a single ground rod, but a cluster of closely spaced rods is considered a single ground point, the 6 foot spacing compensates for differential from one ground point to another.
Many commercial sites have several ground 'test wells' to determine the ground potential differential between different points at the same site.
Still, everything metal above ground is bonded to everything else, and all ground rods are bonded to each other.
This includes towers, buildings, antennas, feedlines, power and telco demarks, even the security fencing.
Everything metallic is connected to ground, and all ground points are bonded to each other.
Ideally, Lightning/Static/EMP flashes over the site uniformly, and finds an effective ground anywhere it touches.
At least that is the theory behind it, not that it always works that way.
Of course when you have 7 to 8 $ figures worth of electronics sitting on the ground, you do what you can to keep everything at an even ground potential, so nothing gets singled out to be 'THE' ground rod.
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