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post #1 of 16 Old 05-04-2011, 05:33 PM - Thread Starter
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I just had Dish Network installed, and I am going to put my outdoor antenna back up to receive local channels OTA. Looking outside, I noticed that the ground wire that the ground block for the Dish cable was connected to was cut for some reason--probably quite some time ago. It used to connect to the water meter outside my home. I have a 4-foot-long grounding rod that I used when I had the antenna mounted before, but it is quite rusty and corroded. These are my questions:
  1. Can I still use the grounding rod?
  2. Can I ground the cables from the dish and the antenna to the same place?
  3. Can I ground the antenna mast to the same place?
  4. Is a cold water pipe a better ground than the grounding rod?
Thanks for sharing any knowledge you might have about this.
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post #2 of 16 Old 05-05-2011, 05:07 PM
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1. A 4 ft grounding rod will ground an antenna and coax but it doesn't meet NEC specs which calls for an 8ft rod.
2. Yes, but each must have its own wire run and clamp to the rod.
3. Same as 2.
4. A cold water pipe is allowed under certain conditions; see Articles 810 (OTA) and 820 (Cable) of the NEC at your library.

To expand on my answers above, I will combine these posts from the thread Would 30% loss make a difference?:
http://www.avsforum.com/avs-vb/showp...3&postcount=30
http://www.avsforum.com/avs-vb/showp...8&postcount=34

There are two reasons for grounding the antenna and the coax. One is to drain any static charge buildup on the antenna system to reduce the chance of a strike. The second is to shunt any leakage current from your AC powered equipment to ground.

There is always some leakage current on the case of equipment even when it is operating properly, and when you have many pieces of equipment connected together the leakage currents add together. With pieces of equipment that have a 3-wire cord, that leakage current is shunted to ground by the grounding pin. With pieces of equipment that only have a 2-wire polarized plug, the potential leakage current exists on the case and coax ground connection.
http://www.avsforum.com/avs-vb/showt...7#post18772087

The 4 foot grounding rods that are sold by antenna suppliers will the ground the antenna but they are not in compliance with the NEC which requires an 8 foot rod, which is sold by electrical suppliers.

If there is a problem that causes damage, you don't want to give your insurance company any excuse to deny payment, which is why you must consider the NEC. You can read about it in the NEC book at the library article 810.

If you use same ground for your antenna as the electrical power ground, then you can use no. 8 aluminum or no. 10 copper wires from your mast and grounding block to the electrical system ground as shown in Wendell's diagram. If you use a ground rod that is separate from the electrical system ground, then you are required by code to use no. 6 copper wire to connect the two grounds together to minimize any difference in voltage potential between them. The electrical people call that bonding. The setup for using separate grounds is shown in this link:
http://www.hdtvprimer.com/ANTENNAS/basics.html

Scroll down to Grounding outdoor antennas.

What we know as a grounding block is called an antenna discharge unit by the NEC.

Wendell's diagram shows the coax running from the antenna to the grounding block, and it shows the no. 10 copper grounding wire from the grounding block to the electrical system ground, but it doesn't show the coax running from the grounding block to the TV. It assumes that you know that.
Update: Wendell corrected his diagram; see post #7 below.

The NEC requires that the ground wires from the grounding block and the mast be separate runs to the electrical system ground with each having its own clamp. This requirement is often ignored in some dish installations because coax with an extra external messenger grounding wire (no. 17 copper clad steel) is used to piggyback the two grounds into one at the grounding block, which then is connected to the electrical system ground using only one wire.
http://www.dbsinstall.com/diy/Grounding-2.asp

http://ecmweb.com/nec/code-basics/el...io_television/

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post #3 of 16 Old 05-06-2011, 08:42 AM
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one of the problems with "cold water pipe" grounding is the extensive use of plastic pipe for residential water service. Unless you are absolutely sure the water utility pipe to your house (and not just the portion going through the foundation wall) is all copper or galvanized steel - don't ground any electrical system to it.

I have seen a bunch of satellite antenna's and mounts grounded to an outside cold water faucet - and often wonder if there is really any "grounding" going on at all.

The other problem with separate electrical grounds and multiple grounding points is they all should be "bonded" to the main electrical entry point ground for the house electrical system. Also a NEC requirement.
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post #4 of 16 Old 05-07-2011, 07:55 AM - Thread Starter
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Thanks for the info, rabbit. I think I'm going to get an 8-ft rod to ground the antenna mast and OTA coax ground block. I was able to connect the ground wire for the satellite coax grounding block to a ground clamp on my service panel where Time Warner cable was grounded.

Vanmeter, the problem with bonding the ground rod to the service panel is that they're about 30 feet apart. That's why I was going to have the separate ground in the first place. Would that long of a run be okay?
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post #5 of 16 Old 05-07-2011, 11:17 AM
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It doesn't matter if they're 3' or 300' apart, an axillary ground rod MUST be bonded to the structure's ground electrode system by a minimum #6 copper wire using listed connectors in order for the grounding system to be NEC-compliant.
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post #6 of 16 Old 05-08-2011, 08:09 AM - Thread Starter
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I kind of assumed that since the max length for a coax ground wire is 20 feet, then the same would apply for the bonding wire. I guess that's an erroneous assumption.

My brother, who is an electrical engineer, told me yesterday that I should ground everything to the grounding rod I put in. He said that otherwise, I could be creating a ground loop because of different potentials. He also wasn't sure that the service panel is a true "Earth ground," whatever that means.
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post #7 of 16 Old 05-08-2011, 08:21 AM
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Quote:
Originally Posted by paligap View Post

That's why I was going to have the separate ground in the first place. Would that long of a run be okay?

As others have stated, the two electrodes (ground rods) must be bonded together (see insert in the graphic below).

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post #8 of 16 Old 05-08-2011, 08:36 AM
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For greater readability:

HOW TO PROVIDE LIGHTNING PROTECTION FOR YOUR TV ANTENNA AND SET
(For outside mount)

Mount lightning arrestor as close as possible to where lead-in enters house. Ground wires for both mast and lead-in should be copper or aluminum wire, number 8 or larger. Lead-in wire from antenna to lightning arrestor and mast ground wire should be secured to house with stand-off insulators, spaced from four to six feet apart.

In the case of a ground up antenna installation, it may not be necessary to ground the mast if the mast extends four or more feet into the earth. Consult your TV service man for proper depth in your area.

The 1993 National Electric Code sets the requirements for bonding the communication, radio, and television antenna and CATV grounds to the power ground in Articles 800-40d, 810-21j and 820-40d. The code requires a minimum No. 6 copper bonding conductor between these ground electrodes and the power grounding electrode, where separate electrodes are used. Please see these articles and Article 250 of the National Electric Code for further detail on the proper grounding of low voltage electrical systems.
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post #9 of 16 Old 05-08-2011, 01:27 PM
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This is what the NEC meant by a static discharge unit when it was alluded to in the 1993 revision.

http://cgi.ebay.com/TV-FM-Antenna-30...item27b9ad5523

As I recall, that term was dropped from the code starting with the 1996 revision and didn't get re-inserted into the NEC until the 2005 revision, at which time it became a common topic of conversation at installer's conferences, as it was undefined. Somewhere, I have a copy of the 2008 version, but I'm pretty sure without looking it up that it now explicitly says that a block that enables grounding of the outer conductor satisfies that downlead grounding requirement.

There was, and probably still is, a bloated-shaped grounding block that has a gas filled spark gap chamber that facilitates static discharge of the center conductor. I bought a dozen of them back in the late 1990s but never used one. I suspect that its internal design was similar to whatever the old twin lead units like the one I linked above had inside them.

Update: lots of manufacturers and distributors are still making and selling it under the part number GRB-AR and calling it a gas tube, lightning arresting grounding block. Here is an old picture of it from a "cable museum" website

http://theoldcatvequipmentmuseum.org.../index.html#GB

The most recent few revisions of the code permit the mast to be grounded by 8 gauge aluminum, 10 gauge copper, or 17 gauge copper clad steel. For several fairly recent revisions, the code had specified that the outer conductor of the downleads had to be grounded with copper wire that was approximately equal in current carrying capability to the cable's outer conductor, which was not defined by the code or by any authority. One electrical inspector who was a ballbuster made me ground an outer conductor with 6 gauge copper. He said that while it probably had less current carrying capability than did the outer conductor, he could rationalize allowing it because, since supplementary rods could be bonded with 6 gauge wire, it would make no sense to require that the connection to that rod be any larger than the bonding jumper.

Quote:
HOW TO PROVIDE LIGHTNING PROTECTION FOR YOUR TV ANTENNA AND SET
(For outside mount)

... Lead-in wire from antenna to lightning arrestor and mast ground wire should be secured to house with stand-off insulators, spaced from four to six feet apart.

The standoff requirement was dropped long ago. Back then, we used to actually twist the flat lead once every few feet to enhance the effectiveness of "common mode rejection." Though not mentioned in the above excerpt but appearing in other, outdated NEC versions cited elsewhere on the internet, the code no longer requires that rotors be wired with flat cables with the outer two conductors grounded, either.

Quote:
In the case of a “ground up” antenna installation, it may not be necessary to ground the mast if the mast extends four or more feet into the earth. Consult your TV service man for proper depth in your area.

I think that exception was dropped because the conductivity of the contact surface of a "planted" mast could not be relied upon, as it might be painted, or might be ferric and rust, can't be inspected, etc.

If someone has the 2008 NEC handy, they may find that there is now a stipulated gauge for grounding the outer conductor that is maybe 10 or 12 gauge. I know a lot of franchised cable companies have long used 12 gauge insulated for that purpose.

One electrician once told me that if you do use insulated ground wire, you have to use green. I work for myself and always use black, just because I consider it to be a little less of an eyesore when run in an eave of white vinyl siding.

While all revisions of the code I have read stipulated that if a ground rod is installed to facilitate mast grounding it had to be 8' in length, I have never seen a minimum dimension for a rod driven to supplement the coax outer conductor grounding. There is a difference between "Supplemental" and "Supplementary" ground rods. One is used to complete the formation of the ground electrode when the soil conductivity is poor and must meet specs identical to those of the main ground electrode, whereas the other is added to the system rather arbitrarily to make a path to earth a little more direct. In 800s subsections for telephone wiring, for example, the code says (or said) that you could use a five foot rod in that application. Hughes satellite internet installers have long been instructed to use five foot rods, which Hughes furnished.
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post #10 of 16 Old 05-08-2011, 03:59 PM
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Wendell:

Thanks for adding the Antenna Lead to TV in your excellent diagram.

If you can not measure it, you can not improve it.
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post #11 of 16 Old 05-09-2011, 06:28 AM
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Quote:
Originally Posted by rabbit73 View Post

Thanks for adding the Antenna Lead to TV in your excellent diagram.

Your welcome.

----------------------------------------------------------------------------

Anyone: It is possible some of the drawing should be updated. If you know of any such updates, please provide them and the NEC reference section(s) and/or number(s). I will add a Rain Drip Loop on the next incarnation of this drawing .
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post #12 of 16 Old 05-10-2011, 06:10 PM - Thread Starter
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Thanks for the information. From this layman's perspective, there is a lot to digest, and some of it seems contradictory. For example, in the OTA FAQ sticky thread in this forum (sorry, I couldn't figure out how to insert the link), there is a document that advises to never use a separate ground rod. In one of the documents that rabbit linked to, it shows that a separate ground rod must be bonded to the electrical system ground.

In another of rabbit's links, it says that the maximum run for a coax ground is 20 feet. That's one reason I thought I needed a separate ground rod--the entry point for the dish and antenna coax cables is at least 30 feet from my electrical system ground. In addition, the antenna mast is over 30 feet away, and the 17 awg copper-clad steel wire I bought to ground the mast is only 25 feet long.

At any rate, I pounded the rod into the ground, so I intend to use it. I plan on grounding the mast and both coax cables to it. Then I'll bond that rod to the electrical system ground. Is there anything wrong with that plan?
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post #13 of 16 Old 05-11-2011, 07:06 AM
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You are on course to do it right.

99% of the time, the grounding system for an outside antenna is directing built-up static charge to ground. With the static charge at zero potential, your antenna is not as much a target for lightning. Ground rod bonding keeps all electrical grounds at the same potential relative to the ground.

If lightning strikes near by, there is the possibility that an "induced charge" will be built up on your antenna as the huge voltage charge of the moving electricity passes the antenna. It does not have to hit it (that is an entirely different disaster), just pass by to cause serious damage to an ungrounded antenna and everything it is hooked up to in the house.
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post #14 of 16 Old 05-11-2011, 07:36 AM
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Quote:
Originally Posted by paligap View Post

...I couldn't figure out how to insert the link...

One way to learn how to do post formatting is to find what you'd like to do in someone else's post, and then click "reply to" that post, as the formatting notation and technique that they used will usually become apparent.
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post #15 of 16 Old 05-11-2011, 09:31 AM
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Quote:


If someone has the 2008 NEC handy, they may find that there is now a stipulated gauge for grounding the outer conductor that is maybe 10 or 12 gauge. I know a lot of franchised cable companies have long used 12 gauge insulated for that purpose.

I do have the 2008 NEC handy. My comments are below.

Article 810 deals with radio and television receiving equipment in the context of this forum. Article 820 deals with CATV (generally master antenna and cable TV systems).

There is no maximum length of either the mast grounding wire, the ground wire from the ADU/grounding block specified in Art 810. That is a requirement in Art 820 that is not present in Art 810. It's not a bad idea to limit the length of the grounding wire, it's just not in the code.

An ADU is not required if the exception in 810.20(A) is followed: " Exception: Where the lead-in conductors are enclosed in a continuous metallic shield that is either grounded with a conductor in accordance with 810.21 or is protected by an antenna discharge unit". Coaxial cable connected to a properly grounded grounding block fulfills this exception.

Art 810.21(H) "The grounding conductor shall not be smaller than 10 AWG copper, 8 AWG, aluminum, or 17 AWG copper-clad steel or bronze". 12 AWG copper clearly does not meed this requirement in Art 810.

There is no requirement that either the mast or the grounding block ground wire be insulated, much less what color it is as pertains to section 810. That electrician probably hadn't read Art 90.3.

Please note that Art 820 has some different requirements that do not apply to Art 810 systems.

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post #16 of 16 Old 04-25-2013, 09:09 AM
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You are right but you are also wrong. A satellite dish is not an antenna in the traditional sense . the TV antenna is joined to the electronic equipment via a wire/cable of some sort. The dish is not. The dish is a reflector. It is no more an antenna than a stop sign at the corner. In 2011, the NEC finally discusses this and makes an exception for 'non-powered equipment and equipment powered by the coax which is not tied back to a cable plant'. Such equipment, ie the lnb, is considered grounded if the coax shield is bonded to the recepticle grounding prong. See 2011 NEC 820.100 and 820.103. Whether you use a seperate grounding electrode or bond to the house electrode, you are STILL creating a new PATH to ground, with a different potential. And in the case something were to happen to the house ground, the coax still becomes the new defacto ground for the entire house, and if you try to turn on 100 amps of equipment, the coax will burn the house down.
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