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Old 17-Dec-2014, 10:54 PM   #1
Flint Ridge
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"Advanced" Grounding

Ok, here is the situation. I have been on a quest for a taller tower and have picked one up. This additional height will get me above all trees and over the hump from a TVFool report standpoint - hopefully placing me in the sweet spot for reception on a weaker station.

Tower is solid legged, each leg to be grounded via #2 AWG solid copper from the tower leg connection to double bolted 8' grounding rod buried min of 6". My antenna will oddly enough be on the top via a mast, clearing other items on the tower. Tower has a mount for a lightning rod as well, but these are normally 6' max and the antenna will probably peak at 13' above the tower.

Is there any good logic in getting the lightning rod higher as I presume my chances of taking a strike are increased with being one of the higher points for miles around, baring other towers. If I should try this, then how?

I've also read a suggestion that placing a grounding block in front of the amp provides additional protection as it would be then directly grounded to the tower mast - Is there benefit to this? I know I'll introduce some additional loss if this is done, but should have it to spare.

Old-timer was trying to convince me that whatever I do, I need to also take the tower ground and get it mated with the house ground, even if that meant just connecting the ground from the planned outlet to the tower ground.

I'm just looking to reduce likelihood of popping my amp and having to scale into the heavens to replace an expensive item. Thoughts and other ideas would be greatly appreciated, thanks!
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Old 18-Dec-2014, 6:29 PM   #2
GroundUrMast
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I know copper isn't free...

OK, a few random thoughts...

If your chief concern is reducing risk of lightning induced damage to mast mounted electronics, a lighting rod above the equipment (including the antenna) would be worth considering.

I agree with the old-timer, that the tower ground system should be integrated into you existing electrical service grounding system. I would not use a #12 or #14 branch circuit ground lead, it's too small in diameter to deal with the current involved with a lightning hit or even near miss. Also, there are likely many sharp bends in the branch circuit cable run which will add impedance at RF frequencies common to lighting discharges. Do you want to invite lightning induced fault current to follow a path though your existing wiring?

I would use a dedicated run of wire, sized for the purpose. Though it's not prohibited by the NEC, I avoid running antenna and mast grounding conductors into or through a structure if at all possible. If there was no guidance from the tower manufacturer, I would use #6 AWG copper (minimum) based on my lay person knowledge of NEC article 810 & 250. Because the documentation for your tower calls for #2 AWG, I would be inclined to go with #2 as the minimum for the bonding conductor from the tower to the new rods as well as the bonding run back to your electrical service grounding system. If your electrical system uses multiple rods and/or connections to pipes, foundation steel, etc, the NEC or local code may dictate an upgrade of the bonding in the existing electrical service ground system. If I was installing your tower on my lot, would replace the #6 AWG that runs from my service panel to the two existing ground rods with #2 AWG. This would ensure that the path from the existing ground rods to my service panel and ultimately the PUD neutral conductor is capable of carrying the current of a ground fault (due to lighting or any other cause) from the new tower being connected to my existing electrical ground system.

Last edited by GroundUrMast; 19-Dec-2014 at 11:29 AM. Reason: sp. / grammar & clirification re. wire size
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Old 18-Dec-2014, 6:39 PM   #3
GroundUrMast
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re. grounding ahead of preamp

The insertion loss of a simple coax grounding block or even one with protection of the center conductor (see link below) should be less than 1 dB. I'd use the type linked to below, but expect it to need replacement if you get hit by lighting.

http://www.solidsignal.com/pview.asp?p=212ff75f225-21

You can see the lengths to which this can be taken...
http://www.nasa.gov/mission_pages/co...lightning.html
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Last edited by GroundUrMast; 18-Dec-2014 at 6:44 PM. Reason: added link
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Old 18-Dec-2014, 8:59 PM   #4
Tower Guy
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In addition to the excellent suggestions by GUM, you might consider replacing the Lightning rod with a static dissipation array. Commercial arrays are expensive, but you can roll your own with a chimney brush.

The purpose of a static dissipation array is to drain off any static before it builds up to the point that lightning occurs.
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Old 18-Dec-2014, 11:25 PM   #5
Flint Ridge
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Ok, this is exactly the kind of validation and new ideas I was looking for.

Thanks GroundUrMast - I was obviously "hoping" to get your input. And I did spend time last night reading 810 and concluding that I would be taking #6 or thicker from the tower all the way around the house to main electrical ground... But now that I think of it I'll be passing my well/hydrant Metal on the way by. Still should just bite the bullet on the 100' of wire. And I knew, but temporarily forgot about the inline protection. I think that is certainly money well spent and might as well get a stack of them as insurance.

Tower Guy, static dissipation array that is interesting as I had been pondering GroundUrMast's idea of putting a lightning rod on top of the antenna. I've got to do some research there - any way to incorporate the two into one or are they distinctly different concepts? Off to research. If I go lightning rod above, do I use the mast as the conductor or do I take a separate wire to the official lightning rod connection at the top?

Thanks!
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Old 18-Dec-2014, 11:51 PM   #6
Flint Ridge
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Static dissipation array - Tower Guy can you shed some more light on the chimney brush concept? I see examples of this out on the internet, and I compare to commercial units that are "pricey" and see discussions about spacing of wires etc.

I really like the idea just need to get comfy with concept and execution.
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Old 19-Dec-2014, 1:02 AM   #7
Flint Ridge
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Looking at the grounding block with surge integrated, what is the difference between the one you cited (nicely on sale) and the other model? Want to ensure I order the proper one. And I know that you probably linked the right one to begin with.
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Old 19-Dec-2014, 11:56 AM   #8
GroundUrMast
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If it's accessible, I'd bond to a Steel well casing which can be an outstanding connection to earth. But... that's not guarantied. The utility neutral is usually the best source of ground so I would still continue my bonding run from the tower and it's rods though to the PUD electrical service neutral, using the size wire called for by the tower engineer.

I don't have detailed knowledge of the guts of the various surge protection grounding blocks. And if I did, it may change with each production run. Still, the general assumption is that they employ some type of solid state device which will 'turn on', shorting the center conductor of the coax to ground if the voltage between the center conductor and ground rises to a certain voltage level. The amount of energy that can be absorbed and failure mode will depend on the exact solid state device used. If the specification is published by the manufacturer, you would look for a high joule value. It can be assumed that even a nearby strike will have many orders of magnitude more joules of energy than any bit of silicon can absorb.

(please note that I edited my first post for clairity)
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Old 19-Dec-2014, 2:47 PM   #9
Tower Guy
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Quote:
Originally Posted by Flint Ridge View Post
Static dissipation array - Tower Guy can you shed some more light on the chimney brush concept?
The brush should have the thinnest bristles possible. They should be trimmed to a hemispherical shape. A separate insulated ground would run from the brush to the bottom of the tower and then bonded to the tower ground and the wire to the electrical box ground in the house.

Tying all the grounds together is the secret to minimizing damage in the unlikely event of a direct hit. What is more likely is a nearby strike that causes currents in the tower and or ground wire. I once observed a lightning strike about a mile away that caused a 20'-30' discharge off the top of a 750' tower. I was 100' from the tower at the time.
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Old 19-Dec-2014, 8:10 PM   #10
Flint Ridge
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Funny, Solid Signal could not determine the differences between the two available, other than color and one was on sale, hence - I'm cheap. Now to design/build a dissipation array of some sort. And source the cheapest ground wire.
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