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Author Topic: Ground wires through the eave or over the gutter?  (Read 4905 times)
NW6V
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Posts: 10




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« on: April 23, 2013, 07:29:56 AM »

Hi.

I'm putting a Glen Martin 4-1/2 foot tower on the peak ridge of a composition roof surrounded on all four sides by eaves and gutters extending 2 feet past the walls of the home.

That is to say, to get coax, rotor cables, the ground wire etc. off the roof they must either pass over the gutters or through the eave.

Over the gutters can be done (A current thread addresses a workable technique for this). This will certainly work but could be a visual mess and requires the wires to re-curve back to the building wall to be routed to ground and/or shack.

Through the eave cable passage can be accommodated by a flashed, short plastic pipe (like vent pipe) extending a few inches above and below the roof surface. I envision doing separate passages for the tower ground and coax/control cables.

I'd prefer the through-the-eave method because it would give me a better run for the ground wire, as well as being more aesthetically satisfactory.

I've studied over the NEC quite a bit lately, and section 810.21(G) explicitly allows a ground wire to pass inside or outside a building. http://ecmweb.com/code-basics/article-810-radio-and-television-equipment gives a good synopsis of NEC 810. There are others.

So, while I'm not crazy about the idea of passing the ground wire through the eave it seems workable, and in this situation, preferable to the over-the-gutter method.

What would you do in this situation, and why?

73, Chris NW6V
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KE7RNK
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« Reply #1 on: April 23, 2013, 08:29:48 AM »

I had the same problem. Solved it by using rubberhose tubing w/ matching color as the gutter. The flexible tubing was bent 90 degrees  and /or inserted in a hole in the gutter which was surrounded with coax seal. Good luck
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WB4SPT
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Posts: 160




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« Reply #2 on: April 23, 2013, 04:56:08 PM »

If the grounding conductor is of primary interest, consider using at least one thrubolt for the tower, and make it silicon bronze.  Attach the copper ground wire in the attic with a crimp ring terminal and double nuts.   This assumes access is possible inside.  I'd use #6 Cu as the conductor, nothing smaller.  As the conductor gets smaller, it will heat more in a strike and become more of an issue with all the wood that is touching it.  Commercial lightning mitigation uses closer to 2/0, but I recall that code is a function of how many stories the building is. I've read where #6 Cu will survive something like 90% of strikes, certainly not all!
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NW6V
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« Reply #3 on: April 23, 2013, 06:08:27 PM »

Thanks for the input.  I like the idea of the throughbolt - I've seen such things listed in sites dedicated to lightning protection of commercial buildings. I do think Nr 6 is adequate for this installation; here in the Portland Oregon area lightning is a relatively rare occurrence, and a so-called "super strike" that would take out #6 is likewise proportionately less probable.

But perhaps I didn't make myself clear: the ground wire will pass from the tower leg, down the slope of the roof to a point about 1.5 feet from the gutter which is outside the perimeter of the building walls (i.e. over the eaves), where it will pass down in a gentle bend through the roof via a plastic pipe like a plumbing stack (vent) and straight down the side of the building to a ground rod (which is bonded to the electric panel). 

The best alternative is to place a piece of thin ply or plastic under the first row of shingles so that it covers the gutter, then attach the ground wire to the support with a cable tie. Once over the roof it now would have to bend back more than 2 feet to the outside wall, then down to the ground, etc. That bend back to the wall will leave a quite visible loop hanging over the edge of the roof, and creates a more indirect path for a lightning charge to follow.

Whichever technique is used, the coax and control cables will be similarly routed, albeit through a separate pipe to a separate bonded ground rod, where all wire leads will attach to lightning arrestors, and then back up the wall into my second story shack.

KE7RNK suggested a rubber hose through the gutter - another possibility I'm now considering.

BTW, just found out the roofer is coming TOMORROW... so whatever I decide tonight is going to be it.

73, Chris NW6V
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N6AJR
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« Reply #4 on: April 24, 2013, 12:34:35 PM »

I just run my cables over the top of the rain gutter along with the ground wire and rotor cables.  it works just fine and has been laying up there for 7 or 8 years.  remember that most likely lighting strike wil probably hit a street lamp or power pole first as they are much higher than your roof  tripod.
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K5LXP
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« Reply #5 on: April 24, 2013, 02:22:40 PM »

Attach the copper ground wire in the attic with a crimp ring terminal and double nuts.   

The idea of a lightning ground is to keep lightning outside the structure, not invite it inside.


Mark K5LXP
Albuquerque, NM
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WB4SPT
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Posts: 160




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« Reply #6 on: April 25, 2013, 05:57:28 PM »

Attach the copper ground wire in the attic with a crimp ring terminal and double nuts.   

The idea of a lightning ground is to keep lightning outside the structure, not invite it inside.


Mark K5LXP
Albuquerque, NM

 A warm wire inside is better than a flaming hole in the roof!
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