Suitable Cable TV ground?

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  #1  
Old 10-05-04, 09:56 AM
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Suitable Cable TV ground?

Reading all these posts about what is adequate grounding and what isn't has me concerned about how the cable TV is grounded in our house. A little background first...

In 2001 we decided to get cable TV. They had to run a cable underground from the street. The installer said the cable had to enter the house within 5 or 10 feet of where the electrical service entered the house to provide a proper ground. This would have been extremely inconvienent since they would have had to dig up a lot of flower gardens, somehow avoid the septic system, and 3 private underground electrical cables that I didn't really know the exactly location of. So instead of coming in the east side of the house, I convinced the guy to come in the North side of the house. I was able to do this based on what is now (in retrospect) a very silly assumption. There was a clamp attached to a cold water pipe in the center of the basement. I assumed that this was a ground for either the electrical or phone service. WRONG...about 6 months after the installation I realized it was an abandoned saddle valve for an old and removed hudmidifier. doh.

Anways, the installer believed this bad advice and mounted the ground (a #18 or #20 insulated conductor) for the cable TV line to a cold water pipe that goes to the hot water heater, and is located on the opposite side of the house where the well pipe enters the house and where the electrical service is grounded. Am I asking for trouble leaving it as it is? Do I have any options other than to have them move the cable to the other side of the house and dig up the rest of the yard?
 
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  #2  
Old 10-05-04, 01:19 PM
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If the cable has a terminal block on the outside of the house, it should have a ground connection. Get a ground rod at R / S or any big box store. Drive it into the ground full depth and attach a ground wire from the terminal block to the ground rod.
 
  #3  
Old 10-05-04, 04:23 PM
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Adding a new ground rod is not the answer. I believe it is also against code.
 
  #4  
Old 10-05-04, 05:09 PM
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Adding an _independent_ ground rod is the worst possible thing that you could do. All of the ground electrodes in your home need to be connected together with sufficiently sized cables.

You have several possible solutions. The important section is NEC 820.40(B)(1).

If you have access (within 20 feet) to properly bonded metal water piping, at a location on the pipe within 5 feet of its point of entrance to the building, then you could bond to this point.

In theory, you could also drive a new ground rod, but then you _must_ connect this ground rod to your home electrical system using copper conductors sized to match your home electrical system. If you do this, then you could connect the CATV ground to the 'grounding electrode conductor'. The important thing here is to maintain a _single_ grounding system.

-Jon
 
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Old 10-05-04, 07:53 PM
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My bad - I guess. I have a dish system and it recommends the ground rod approach I mentioned in my earlier post. I always considered cable as a remote antenna. Having installed a number of ham antennas over the years, they are always grounded via direct earth grounds, not tied to the house grounding system.
 
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Old 10-06-04, 04:42 AM
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You can use the "additional ground rod" approach. The downside of it, is you have to connect the new ground rod to the existing grounding electrode system anyway (which is a heavy conductor). So you might as well run the proper bond conductor from the antenna to your grounding electrode system (within 5' of the entry of your cold water pipe or other).
 
  #7  
Old 10-06-04, 05:27 AM
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There is nothing wrong with a direct earth ground for an antenna...as long as it is properly bonded to your main ground system! (or properly electrically isolated from your main ground system...hard to do if you are running cables between the shack and the antenna.)

It is a common misconception that electricity 'seeks earth', and that the ground rod provides safety as long as it is connected to earth.

In fact, electricity does not seek earth, but instead seeks to return to its source. For reasons of lightning protection and insulation protection (both increasing over-all safety), your electrical system is 'grounded', meaning that the electrical system is connected to an earth electrode. This connection makes it possible for the earth to be a path for electricity seeking its source. (Note: there _are_ ungrounded electrical systems; they are for a separate discussion )

If, for _any_ reason, you have current flowing in the earth, then this current will follow _any_ available parallel paths. This means that if you have two ground rods buried in the earth, electrically connected together, that earth currents will flow through the wire connecting the two ground rods. This is not a problem if the two ground rods are well bonded with a thick copper conductor.

But if one ground rod is connected to one system (say your CATV or telephone system) and the other ground rod is connected to your electrical system, then this current could end up flowing through very thin ground conductors tying these two systems together. And if there are no good ground current paths, then you can get extremely high voltages present between the two 'grounded' system.

I am sure that in the ham antenna that you've installed, you not only placed ground rods at the antenna, but also ran some beefy ground wires between the shack and the antenna!

-Jon
 
  #8  
Old 10-06-04, 08:20 AM
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Thank you for the replies. What would be the problem with extending the current #18 insulated ground wire another 40 feet accross the house and connecting it to the pipe near the water well entrance?

To me it seems that because they use such a small conductor to ground the entire CATV system, they aren't really protecting against lightning strikes. Is this a bad assumption?
 
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Old 10-06-04, 08:23 AM
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Grounding of your electrical service, your cable TV line, and your phone line is not to protect against lightning strikes.
 
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Old 10-06-04, 08:31 AM
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I believe the minimum size for the grounding conductor is #10 copper or #8 aluminum. NEC 810.21(H)
 
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Old 10-06-04, 09:03 AM
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DIYnovice,

If I am reading the NEC correctly, you have to make the connection between the CATV system an one of a number of allowed grounding points. There is an entire list of the allowed grounding points. The connection has to be within 20 feet of the CATV entrance. So running the skinny grounding wire 40 feet across the basement is not an option.

I believe that your only option is to extend your grounding system (following the rules of article 250 of the NEC), until some portion of the grounding system is 'in reach' of the CATV entrance.

However at this point I have to concede that I am swimming beyond my experience level. Please wait for a couple of the professionals to chime in before acting any of the amateur advice (including my own.)

-Jon
 
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Old 10-06-04, 09:40 AM
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This is all very confusing to say the least.

Why does the CATV need to be grounded when it's just a signal conductor? Is it for my protection of the Cable company's protection?

I just went up and looked at it up close and determined it is a #12 conductor - much larger than I first thought but still not large enough.
 
  #13  
Old 10-06-04, 11:44 AM
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Perhaps take a look at this document on grounding/bonding of CATV drops. It should help to clarify matters a bit for you. (it also explains why you shouldn't put in a separate ground.)

My thoughts are that it might be better to clip the drop to the outside of the house, and bring it inside near the meter. That way you get your ground and don't have to worry about digging. The other option would be to consider running a cable inside the house (from the main ground clamp or other suitable locaton) to serve as a ground for the drop. If memory serves me correctly, once the ground clamp is in place there is no maximum length restriction for the actual ground wire (inside) in residential applications, however one shouldn't make it any longer than necessary.

Regards,

Savant
 
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Old 10-08-04, 01:34 PM
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Thanks for that link, it's very informative. It states that a #12 grounding conductor is sufficient, so it looks like I'm OK there. But upon checking out where the grounding wire is connected at the service entrence, I found that it's behind the locked door of the service box attached to the outside of the house. So it appears I'm SOL if I want to correct the problem myself and keep it up to code. I'm afraid that if I decide to get the cable company involved in this they are going to want to dig up the yard again and charge me an arm and a leg for it.

What would be the real harm in extending the current grounding wire another 30 or so feet to connect it to the location where it should be? I realize it would still be against code, but wouldn't it be better than the way it's currently set up?
 
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Old 10-08-04, 04:47 PM
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I don't know what grounding wire you want to extend... Do you have a cold water ground? (not counting the one you thought was a cold water ground) In any case, as far as I recall, you are allowed to run a ground wire indoors to use as a ground, so long at you connect it to a proper ground source. (EG. copper cold water pipe within 5 feet of entering the house BEFORE it reaches the water meter) Since this isn't a service ground the code is a bit more flexible. The reason they want the CATV drop near the service is since there is an available ground nearby. In many houses you can't run a ground inside since the house is finished. So it's not a code requirement to run the CATV in near the service, it's just good practice. So long as the CATV feed is properly grounded then it really shouldn't matter where the drop is run in.

I wouldn't mess around with the ground line for your house if you only have to run a #12 ground for the CATV. Just run a ground line indoors from a location where your cold water pipe enters the house (as noted above) and then run that ground line to the point where you need the CATV drop grounded. You are allowed to do this indoors. It's the outdoor runs that get more complicated. If your indoor ceiling is open I would just go at it this way and you'll be done in no time flat. (when running the ground indoors make sure you treat it like you would any other electrical cable and secure it properly etc)

Regards,

Savant
 
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Old 10-08-04, 07:03 PM
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Sorry for being vague in my last reply, everything was in reference to the #12 CATV grounding wire. I cannot access the point where it originates because the CATV box attached to the outside of the house is locked shut.

This #12 ground is clamped to a cold water pipe which is 50-60 feet away from the well-water entrence. The only choice I seem to have is to extend the existing #12 ground to the same cold water pipe as the electrical service ground by splicing the exisiting #12 ground.

Is splicing allowed by code, if so would a simple wire nut connection suffice? I am not considering altering the main electrical service ground in any way. Thanks again for all your help.
 

Last edited by DIYNovice; 10-08-04 at 07:18 PM.
  #17  
Old 10-08-04, 08:15 PM
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If I recall the NEC correctly, the ground has to be one continuous line. That means no lugs, split bolts, wire nuts etc. However, I have heard that if you use a non-removable type connector then it would be passable. (although I have never done it myself, I prefer to use a single run, even if it means a repull)

Non-removable would be some form of compression crimp connector for stranded wire or an exothermic weld for solid wire. Since this is a relatively small gauge, you're likely using solid wire. As such, only a exothermic weld would be acceptable. It would be easier to just connect your ground clamp to your proper ground source, then run your new ground wire right to the CATV drop.

Give the cable company a call and say you have done renovations and the ground wire to their drop was removed and a new ground wire put in it's place. Ask them to come and connect the ground into their demarc box. I would think there shouldn't be a charge since it's demarc related. Exothermic welds are not really a DIY type thing. Perhaps call and ask if they would charge you for it. That would be the simpliest way.

Regards,

Savant
 
  #18  
Old 10-09-04, 04:33 AM
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RaCraft.
"Grounding of your electrical service, your cable TV line, and your phone line is not to protect against lightning strikes."

I sorta agree, cuz a direct lightning strike will probably cook every electrical devive in the house regardless.

Then, if it's not for lightning, why does a low voltage cable(or Sat) system need to be grounded anyway???

fred
 
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