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Ways to ground roof-mounted Sattelite Dish

Posted by dgeist (My Page) on
Sat, Dec 15, 12 at 9:15

I recently moved the RG6 conductors between my satellite multiswitch and the exterior dish from a path that exited a crawlspace and ran up the side of the house. The new path is shorter and is concealed by using interior framing cavities, then through the attic floor, and up to the eaves. Originally, there was a grounding block with a conductor running down the side of the house to a clamp on an outdoor water spigot (not the best ground, but good for the house since my house electrical ground is still my cold water supply).

I'd like to NOT have a ground conductor running down the side of the house (aesthetics), so I'm thinking of putting a ground block just inside the attic (close to the penetrations in the eaves) and connecting to a ground inside the structure.

If I do this, can I connect it to the ground in an existing lighting branch circuit located in the attic or am I better off running a dedicated conductor down through the house to connect as close as possible to the building ground connection? I.e. would the "lightning ground" for the satellite have different grounding characteristics than your typical conductor in residential branch circuit?

Your thoughts and suggestions are appreciated.

Thanks.
Dan


Follow-Up Postings:

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RE: Ways to ground roof-mounted Sattelite Dish

This is a silly idea. The last thing you want to do is to bring something that's a lightning succeptable inside the house and hook it to some branch circuit grounding conductor. You might as well leave the dish ungrounded. T


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RE: Ways to ground roof-mounted Sattelite Dish

Thanks for your constructive comment... Anyone have any comments that might actually be helpful in some way?


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RE: Ways to ground roof-mounted Sattelite Dish

You are actually required to have TWO ground conductors connected directly to the building's electrical ground bonding system. One, for the mast/support and dish itself, and the other for the coax antenna discharge unit.

They must be unbroken 10 AWG copper, or larger, run in as straight of line as possible, and can be stranded, solid, insulated or not, in whatever color you please, or run in PVC.

Terminating to a bonded water pipe within 5' of point of entry is allowed but attached to a water spigot is not.

And, believe it or not, you can run it inside or outside the building, however just like Ron, I would never even consider it.


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RE: Ways to ground roof-mounted Sattelite Dish

Do not invite lighting to enter as part of its path to ground.

It has a really nasty habit of NOT following the path you intend, especially if there are sharp bends in the down line line.

A direct strike is rare, but nothing you have for grounding the antenna will be there after a direct strike.


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RE: Ways to ground roof-mounted Sattelite Dish

Good info. Thanks.

So it sounds like the primary ground (for the mount and frame of the dish itself) really needs to remain on the outside of the house and bond to the water supply in as straight a path as possible. I would assume that's going to take the lions share of the juice in a direct strike... since the LNBs are encased in plastic and not electrically joined to the frame.

As for the RG6, does it make much difference (other than obviously having the current travel the length of the run) if I put a grounding block for the pair at the end close to the dish or the end close to the multiswitch? It would be much easier to tie it to the building ground at the latter, avoiding using branch circuit grounds unnecessarily.

Dan


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RE: Ways to ground roof-mounted Sattelite Dish

The two grounding systems provide for different types of basic protection, but there is also overlapping protection.

The bonding of the mast/support/dish provides a path for direct lighting strikes, indirect or nearby lighting strikes, and static build-up across the dish caused by wind and clouds.

It also provides protection from high voltage contact such as fallen power lines. It must also be bonded to swimming pool/hot tub ground bonding systems as well if within 5 feet of either.

The coax ADU (antenna discharge unit) mainly provides for depletion of static charges, from the dish and exposed coax, that would otherwise build-up and jump across the dielectric barrier of the coax and directly into your satellite receiver and the rest of your entertainment equipment.

While static can be fun for sticking balloons to things it wipes out semiconductors in your home entertainment equipment in a heart beat.

In addition, the ADU usually eliminates those little sparkly things that appear on your television screen. The ADU will also help dissipate any lightning created energy as well.

Typically the mast grounding is done by a drop from dish/antenna to a bonded ground. The coax usually enters at ground level and the ADU is a short jumper to the building's electrical ground.

What the two DBS companies usually recommend to installers when the coax enters the building up top (with a wink and a nod) is to tie a continuous bonded ground from the mast on over to the ADU. But they also acknowledge it does not technically meet NEC and then add it must be done to any prevailing local code. Most of the installers are 1099 contractors so they face those liability issues themselves. While not proper, at least do that if you must.



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RE: Ways to ground roof-mounted Sattelite Dish

If you think the LNBs being encased in plastic will protect them from a 50,000v lightning strike, you are incorrect.

You don't need to ask me how I know.


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RE: Ways to ground roof-mounted Sattelite Dish

Indeed! Not much would protect it in that case. In a direct strike, I'm going to be more worried about where my fire extinguishers and kids are than if the DVR is still recording ThisOldHouse...

YB, I'm curious about your (paraphrased) "Sat. companies recommend but it's not to NEC" comment. Are you saying that by the strict letter of the code, putting the ADU anywhere other than at ground level is not permitted (where it'd be tied to building ground) just because that's how it's written, or that tying it to the ground used for the sat/antenna frame AT the frame would actually offer less protection? The only thing I can think of why that would not be permitted is that it's functionally a chained connection to ground instead of being unbroken, but I might be missing something obvious.

Dan


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RE: Ways to ground roof-mounted Sattelite Dish

Typically the dish is mounted on the roof and the POE (point of entry) for the coax is near the foundation. The mast ground is run down the outside of the home along with the coax. The mast ground is bonded as required and then an ADU is added to the coax before entering the house, and it is separately bonded.

The grounding of the mast and coaxial ADU are addressed under two separate NEC articles and each require ground bonding. There is a little ambiguity as to whether they "could" use a shared ground but think about what happens when you share that grounding conductor at the mount for a coaxial feed into the attic space.

Lighting will take the path of least resistance - so now you got 15-20 feet from the mast down to the ground bond, or 2 feet to the coax ADU, and then down the coax to the inside of your home.

While this will probably not make much of a difference with a direct hit, as everything will be toast, a nearby strike were a finger of lightening touches the dish may be able to be dissipated through the mast ground.


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RE: Ways to ground roof-mounted Sattelite Dish

Don't even worry about it. If you get a direct hit you had better have prearranged funeral plans. everything is done. Ground or no ground. I had a strick come down across the road. About 1/4 mile away. Lost the TV., Phones,( actually they started ringing ), LNB, receivers, stereo, speakers, computer, microwave, Etc,etc,etc. It also took out one window. and there is a typo in weedman's post. A lightning strick can be up to and over 50,000,000 volts. Another strick came down maybe a few miles away. Didn't know what
one but later on i found my rotor motor and preamp on my
mast roasted. Actually burned and it was grounded by a #4.
Your RG6 and anything connected to it will go up like a cannon fuse if there is a direct hit so i wouldn't sweat the grounding. " I said direct hit ". Even a mile or so away can do serious damage. Been there paid the price.
OH YA. the big one took out the computer in my car. Needless to say this one scared the piss out of me. Yes i was very scared and it set the bush on fire. This was in a rain storm.


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RE: Ways to ground roof-mounted Sattelite Dish

"About 1/4 mile away."

Along with the high voltage comes very high currents.

The currents create a very powerful magnetic field that quickly rises in strength and then decays.

This rapid change allows coupling into ANYTHING conductive that the field passes through, producing current flow and high voltages.

When I had a roof of antennas for electronic warfare work on a 6 story building we had four down wires almost 1.5 inches in diameter (2000 MCM) each of bare stranded copper to deep drilled electrodes.

It took a number of direct hits over the years, usually making the actual antenna disappear (as in gone) and damaging adjacent antennas.

We had to run the down wires since the re-bar in our concrete building had not been specified as welded.
When we had a hit using the concrete as our ground it destroyed all the antennas and most of the receivers and equipment hooked to them.

This post was edited by brickeyee on Fri, Dec 21, 12 at 10:21


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