Rooftop Antenna Grounding - AVS Forum
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post #1 of 22 Old 03-06-2012, 01:04 PM - Thread Starter
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I understand that, according to NEC code, you need to ground both the coaxial cable and the antenna mast in a rooftop installation. I was curious as to why you need to ground both and not just the coax? My understanding is that there are 2 types of coax grounding mechanisms - a 'grounding block' which grounds the outer shield of the cable and a 'lightning arrestor' which grounds the central conductor of the cable. Do the NEC rules assume you are just using a grounding block and therefore don't have a way to stop a strike getting into the house via the center conductor? Or is grounding the antenna simply a way of taking some of the load off the coaxial cable in the event of a strike?
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post #2 of 22 Old 03-06-2012, 01:28 PM
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My rooftop antenna coax is grounded where it comes into the garage to the cable tv ground connector that was installed when the house was built. This is before the feed goes into the splitter and off to the house. We don't live in a high lightening strike area so I'm not sure how effective that would be in a direct strike but hopefully it would take out the neighborhood cable before seriously affecting us.
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post #3 of 22 Old 03-06-2012, 02:43 PM
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Quote:
Originally Posted by Ferrino View Post

I understand that, according to NEC code, you need to ground both the coaxial cable and the antenna mast in a rooftop installation. I was curious as to why you need to ground both and not just the coax? My understanding is that there are 2 types of coax grounding mechanisms - a 'grounding block' which grounds the outer shield of the cable and a 'lightning arrestor' which grounds the central conductor of the cable. Do the NEC rules assume you are just using a grounding block and therefore don't have a way to stop a strike getting into the house via the center conductor? Or is grounding the antenna simply a way of taking some of the load off the coaxial cable in the event of a strike?

Hi Ferrino,

Search the HDTV Technical forum with the following keywords: "lightning arrestor center conductor" and you'll find some excellent info.

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post #4 of 22 Old 03-06-2012, 03:44 PM
 
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To make things simple, the Antenna & mast can separate at any time, and bonding both the coax and the mast at the common Earth ground, means that you are covering your bases in case either gets separated during a storm, or hit by a tree, and become energized at any time during that situation. If you look at the sections of a antenna, they are held in place by plastic blocks to keep from coming in contact with the main assembly that attaches to the mast.

Pretty much cut and dry, plain and simple. BTW, the mast/antenna should be bonded to Earth ground with a #8 wire in the straightest and shortest path to the ground rod or Ufer bonding point. The coax ground block should be grounded to ground rod or Ufer using the shortest and straightest run possible. You can use #10 for the ground block, also suggest using a Gas Discharge as a extra safety measure.
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post #5 of 22 Old 03-06-2012, 03:52 PM - Thread Starter
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Thanks very much! I'm currently trying to use an attic-based setup, but would like to know what's involved if I move it to the roof. Running a ground wire from mast to ground would be a big effort due to the structure of the house.

2 more questions:

1. Could you avoid the need for a mast ground connection by using a non-conductive mast, for instance PVC?

2. Even if I was to retain an attic installation, is there an advantage to using a coax grounding block? i.e. can the coax line still be subjected to static build-up that may interfere with signal? The way my coax is wired, it would be trivial to insert a grounding block and connect it to the service panel ground.
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post #6 of 22 Old 03-06-2012, 04:36 PM
 
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You still jave to ground the antenna, regardless of the mast material. As for the attic install, it is in the house, you do not have to install a ground block or ground it. Common sense prevails.
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post #7 of 22 Old 03-06-2012, 05:16 PM
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Quote:
Originally Posted by Ferrino View Post

...
1. Could you avoid the need for a mast ground connection by using a non-conductive mast, for instance PVC?

No.

Quote:


2. Even if I was to retain an attic installation, is there an advantage to using a coax grounding block? i.e. can the coax line still be subjected to static build-up that may interfere with signal?

No, a grounding block is not needed in an attic. The static charge builds up outdoors, from the wind blowing across the antenna.
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post #8 of 22 Old 03-07-2012, 06:49 AM
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A nearby lightning strike can still induce a surge in to the attic antenna. Your best bet is to ground the cable, along with a surge-limiting lightning-arrestor.

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post #9 of 22 Old 03-07-2012, 09:28 AM - Thread Starter
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Thanks! The reason I asked about using a ground block is because I read that it can improve a fringe signal. Also, the coax line actually has to run outside for about 20 ft. before re-entering the house.
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post #10 of 22 Old 03-07-2012, 09:49 AM
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The ground can also provide a backpath to your antenna/equipment, when lightning hits something nearby and goes into the electrical ground system.
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post #11 of 22 Old 03-08-2012, 10:15 AM - Thread Starter
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Quote:
Originally Posted by arxaw View Post

The ground can also provide a backpath to your antenna/equipment, when lightning hits something nearby and goes into the electrical ground system.

Are you saying that this would be a reason not to ground the coax in an attic-based antenna installation?

This was the section I was referring to, taken from http://www.hdtvprimer.com/ANTENNAS/basics.html:

Quote:


Indoor antennas (including attic antennas) are not generally susceptible to direct strikes. In such cases a grounding block is not required by the rules, but is probably a good idea when the cable is longer than 30 feet.

My coax line from antenna to TV is in the region of 100 ft (with pre-amp), so I think I'll use ground the coax shield using a grounding block connected to the service panel.
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post #12 of 22 Old 03-09-2012, 11:48 AM - Thread Starter
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Sorry, I have another question about grounding. One of the reasons I have been put off a rooftop antenna (compared to within an attic) is the pain of running a grounding cable to earth (it's a 3-storey home with a very long run from roof to ground). The area where I would install the antenna is actually very close to a solar panel which heats our water system. It obviously has an array of metal pipes that feed into the water tank, which are all exposed and could also serve as lightning rods. How are these pipes grounded and could I ground the antenna through them instead of running a long cable to a grounding rod in the earth?
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post #13 of 22 Old 09-11-2013, 12:35 PM
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What is the correct way to run a mast ground wire across the roof?
My mast on the second story, I understand the ground wire must remain outside of the house to the ground rod.

What is the correct method to secure the wire to the roof, and run it down the wall of the house to the ground rod.
Taking aesthetics into the mix.
Siding is metal.
Thanks.
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post #14 of 22 Old 09-11-2013, 02:26 PM
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The NEC specifically permits the mast's ground wire to be run either inside or outside, regardless of the difference of opinion by internet posters. Reference NEC 810.21(G).
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post #15 of 22 Old 09-14-2013, 05:11 PM
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For my antenna I drilled a ½ " hole through the roof just below the antenna mast. I ran the coax, rotor and ground wires through the roof into the attic. The ground wire is connected to the ground in an electrical box in the attic which I installed just to power the amplifiers and work light. The electrical power is a straight run to the main breaker box. All the amplifiers are just under the roof so the run from the antenna to the amplifiers is about 8 feet.

The ½ " hole in the roof was tarred to make it water tight.

In my climate I sometimes have to shovel the snow from the roof so outside wiring sucks. This is a very neat way to keep the wires out of the way.

The inside cables go from the amplifiers down through the walls to outlets near the TV's. All the wiring was mostly kept in the attic and walls.
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post #16 of 22 Old 09-15-2013, 11:07 AM
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Please note, " grounding" still needs to be the single point. It is against the code, and can cause lethal voltages, to put in a ground rod at the antenna that is not "bonded" which means connected, to the main earth ground where your entrance comes in. US electrical code. Other countries may differ.

Yes, the mast needs to be grounded. The coax shield needs to be grounded, and it does not hurt to put in a spark-gap arrester for the main lead. ( you don't ground the center. If you did, you would get nothing) Another trick is that high voltages do not like sharp corners. I bring my down lead into a loop of about a foot right off the ground. That is also were the shield ground block is. The mast ground comes straight down here next to it into a 8 foot ground rod. That rod is then tied with 10 ga copper back to the main entrance ground rod on the other side of the house. The county inspector liked this install. Then the utility company came by and said they don't care if it passed code, they have their own code and I was a foot too close to the overhead. It seems the Governor threatened the utilities as they had not been trimming any trees for years, to enforce the letter of the law on line clearance. So, instead of a very solid 5 foot mast that has been there for 50 years,, I am about to move it to a flimsy 20 foot mast that if it were to fall over, would hit the lines, but it will be by their code.
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post #17 of 22 Old 09-15-2013, 11:14 AM
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Quote:
Originally Posted by ProjectSHO89 View Post

The NEC specifically permits the mast's ground wire to be run either inside or outside, regardless of the difference of opinion by internet posters. Reference NEC 810.21(G).

Absolutely correct, as long as it is running back to the main entrance ground. I think it is permissible to pick up a water line if they are copper. I believe it is not permissible to just tie to an outlet.

On the inside of almost every audio unit is a nice full picture and description. Seems stupid my DVD payer came with this as it has no antenna, but that is what the lawyers seem to think is necessary. In the vernacular: RTFM.
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post #18 of 22 Old 09-16-2013, 03:55 AM
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Quote:
I think it is permissible to pick up a water line if they are copper. I believe it is not permissible to just tie to an outlet.

There is no substitute for knowing instead of just "believing". Consult a copy of the NEC to see what are the permitted means of grounding. They are all listed there.
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post #19 of 22 Old 09-17-2013, 01:34 PM
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Correct, which is why I did not state it as fact. I don't happen to have a copy and for some reason, they are very hard for a non-licensed electrician to obtain. Even our county code just references the NEC. My library had a copy so old, it did not even cover the arc-fault changes. "Just read the code" is not much help to the average person.
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post #20 of 22 Old 09-17-2013, 04:21 PM
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Here's a tip for getting a free copy as a PDF.

Certain states, counties, and cities incorporate the NEC as part of their laws or building codes regarding electrical work. When they do this, they often include a copy of the adopted NEC in the copy of the law or code. I think you can find a copy of the 2011 version in the applicable law or code from North (or was it South) Dakota.
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post #21 of 22 Old 09-17-2013, 04:44 PM
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Grounding to a cold water pipe is fine from a technical point of view, but not permitted by "the code", because it is not always possible to certify and maintain the integrity of a water pipe ground path since repairs may be made to that pipe with plastic parts. I believe that it was the 2002 code revision that says you can only attach to a cold water pipe if the attachment point is within 5 feet of where it enters the building. At that time, there was an exception for commercial buildings that permitted the attachment to a cold water pipe anywhere as long as the plumbing was substantially exposed and professionally maintained, but when I eyeballed the 2011 revision, I didn't see that exception still being in there. If you are only concerned about safety, rather than accommodating the mattress tag police, and if you know the cold water pipe to be continuous to its point of entry in the building and bonded to the grounding electrode system, then if you ground to it, you would have a ground that is as good as code, but not in conformity with it. If you go way, way back, there are old revisions of the code that permitted grounding to a gas line, and versions that required the downlead to be on standoffs 3" from the side of the house, and there used to be a requirement that the rotor control cable have both of its outer conductors grounded, so old rotors that needed four wires for control actually had to use five conductor wire. Those were the days...
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post #22 of 22 Old 09-18-2013, 06:49 AM
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Agree - using copper piping is actually a better bonding method then 6 awg wire, due to much lower impedance. However as posted the problem is that in the future a section of copper will be replaced with plastic severing the bonding connection.
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