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#191482 12/30/09 10:14 PM
Joined: Dec 2009
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bass1 Offline OP
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Catv cable is bonded to power ground at one location in a home and then again bonded to a copper cold water pipe in a home that is also tied to the power ground system thus it is double bonded.The question is this hazardous?Some Electricans say yes it is hazardous some say no which is it and is there any documentation to support the claims either way.

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bass1 #191486 12/30/09 11:38 PM
Joined: Jan 2004
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I don't understand the term "power ground" but assuming you are talking about the electrical "System Ground" and also to the copper water pipe elsewhere in the home, I don't see this as a problem. The code requires you to connect the shield per Article 820 Section 820.100 NFPA70 2008 Edition. Now if you want to additionally bond to the water pipe somewhere else, albeit not necessary, be my guest as long as you have complied with the afore mentioned section of the code.

Greg- This is your specialty -What say you?


George Little
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How far is this from where the water pipe comes into the house?
Multiple bonding doesn't bother me but I wouldn't want the CATV cable to be the bonding jumper around a dielectric fitting in the piping system.
Generally speaking I would want my cable bonded as close to the grounding electrode as I could get it and then at a surge protector at the TV, bonded to the EGC.


Greg Fretwell
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bass1 Offline OP
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Sorry for delay been on vacation.There is a bond 10'from the point of entry into the home bonded to the grounding system ground braid.The other bond is at a 2-way splitter in the basement 25'or so away from the water pipe entry into the home at a copper water pipe with a water pipe clamp 2' of wire from the clamp to the splitter ground screw.

bass1 #191673 01/06/10 11:10 PM
Joined: Oct 2006
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E
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It should be bonded only once, just like all other utilities.


---Ed---

"But the guy at Home Depot said it would work."
Joined: Jan 2004
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Ed- Possibly you could give us some code references or documentation? We are not talking bonding a neutral conductor here. This is not a current carrying conductor. Sorry for being so curt here but I think you are mistaken.


George Little
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I was curious about that too.
It is going to be bonded incidentally along the way several times so that ground loop thing is meaningless.
I know on some transmission lines the design goal is to only bond the braid on one end so it doesn't carry eddy current but when you are talking about CATV they get bonded at the pole, the ground block/surge protector at the house, the splitters (if you use the bond lug) and maybe even the cable box. I haven't checked the point of use protectors but I wouldn't be surprised if they bond the braid too.


Greg Fretwell
Joined: Oct 2006
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Sorry, I have no code reference as I don't know of it being an NEC issue myself. My son is a technician for Comcast and I ran this by him, although he referenced 820-41 and 250-71(b). Now that I've looked, neither of those articles appear to address this question specifically in my mind.

I really can't say for sure except that he said that they are trying to avoid the presence of ground loops and the inevitable non-metallic plumbing isolation being carried by the cable shield. I guess that part would make sense from a precautionary standpoint.


---Ed---

"But the guy at Home Depot said it would work."
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From an EMC and RF shielding point of view, the answer to where and how often do you bond, is "it depends".

If you are shielding to minimize RF (Radio Frequencies) from getting in or out of the cable, the answer is everywhere you go thru a bulkhead and both ends of your shielding.

If you are shielding for Low Frequencies (Audio and the like) Then TYPICALLY you bond at only one end of the shielding, where most of the shielded cables terminate. Usually at the mixing consoles, equipment racks, etc.

CATV signals definitely falls under the RF classification, therefore I would bond the shielding at every point available. One thing to watch out for, is that the RF shielding does not become the bonding conductor for something else. Stray currents running down the shield can play havoc with video signals.

Larry C


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