Bad AC House Ground?

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  #1  
Old 07-22-04, 07:27 AM
Bubbamill
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Bad AC House Ground?

I have a problem with my cable TV service that may be related to the AC ground in my house.

All of my TV's display a hum bar which looks like a dark horizontal bar that slowly scrolls vertically up the screen. I have tried all sorts of filters in the TV cable both at the TV's and an the point where the cable enters the house. Nothing helped.

The cable TV company (Comcast) sent a technician. After trying various things with no success, she tried disconnecting the wire that went from the cable grounding block (where the TV cable enters the house) to a cold water pipe in my basement. Once the wire was removed, the problem disappeared. She tried grounding the cable TV block to various cold water pipes in my basement and even tried connecting to the brass water meter. The meter has a large wire bridging the source and output sides. She even tried removing the wire and clamps and cleaning the connections. Nothing helped. She then concluded that I must have a bad ground coming in from the power company and that I should contact the utility for help.

I called the power company, but they told me that there was no way it was their problem. They told me that they would have to charge me to come out and diagnose what most likely was a cable TV issue. The utility feed is buried and connects to a transformer in my neighbors yard.

So now what? Could I really have a bad house ground from the utility? Is there any way I can run my own tests? I am not comfortable running with the ground wire disconnected from my cable TV feed block. Any ideas to help me solve this?

Thanks!
 
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  #2  
Old 07-22-04, 10:41 AM
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One of the 3 Service-conductors from the utilty supply that terminate on the meter-socket is a "Neutral" conductor. At the premises, the Neutral Service-conductor is required to be connected to a Grounding Electrode. The most common type of Grounding Electrode is a metallic, underground, water-service line.

The wire clamped to your water-meter is the wire that effects "Grounding" the Neutral Service-conductor to the Grounding Electrode. When so Grounded, the Neutral Service-conductor is also referred to as the GROUNDED Service-conductor and is required have a positive identification, which is a White color ONLY.

All Grounding connections at the Service are the responsibility of the customer.You MAY have "leakage-to-Ground" at some point in the interior wiring system which may be the cause of the interference with the cable system.

I suggest you Ground the TV to a seperate Ground-rod ( 8ft depth) and "Bond" the TV Ground-rod to the System Ground with a #6 copper conductor.

This arrangement is described and illustrated in the NEC 2002 "Handbook", pages 206-207.

Good Luck & Enjoy the Experience!!!!!!!!!!!
 
  #3  
Old 07-22-04, 11:36 AM
deep6blue
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"You MAY have "leakage-to-Ground" at some point in the interior wiring system which may be the cause of the interference with the cable system."

Could this be solved by cycling through the breakers to see which circuit is causing the interference? Once the circuit is located, each outlet/switch should be checked for a faulty ground connection.
 
  #4  
Old 07-22-04, 12:42 PM
Bubbamill
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Actually, I did cycle every breaker with the exception of the one that ran the TV. The hum bar was there the entire time.

The large wire across the water meter appears to be bare aluminum.

It would be difficult to directly ground the TV as there are 4 TV's involved on different floors of the house.

One other data point. The power company has had to repair my underground utility feed twice in the past 20 years. The first time was shortly after I had a fence installed in 1985. Apparently the installer nicked the buried cable while digging a post hole. The second time the utility cable failed was in 2003. They had to go back in and repair the original repair from 1985!

PATTBAA, are you saying that the utility ground is local to my house? That they simply connected a wire from my buried copper water supply line and brought it into the service panel? I guess I had assumed that the utility feed from the street transformer included the 3 wires for the power plus a separate ground wire for the breaker box.....
 
  #5  
Old 07-22-04, 02:01 PM
deep6blue
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My thoughts were not exactly clear. When I mean cycle, I meant to actually turn the circuits off. Then turn them on one at a time to see which circuit has the grounding problem. Of course you will turn on a circuit with a tv on it first.
 
  #6  
Old 07-22-04, 07:17 PM
CSelectric
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You may have quite the complex problem on your hands. If I understand correctly, you have shut off all of the breakers in the house, except for the circuit powering the television and the screen problem did not cease? For starters, plug your TV into a different circuit, then shut off the circuit the TV was operating on. This will rule out that circuit as a source of the problem.

Beyond that, you will probably want to consult an electrician. It certainly sounds as though you have stray current on your cold water system. through a series of tests (with your main breaker on and then off) the electrician will be able to determine if the ground leakage is in your house or coming into your house via the underground water service. I have seen several cases of stray ground currents on an incoming water system. Usually this is caused by a faulty connection at the power company transformer, but can also be caused by a leakage to ground on a neighbors electrical system. Unfortunately, there is no reasonable way for a homeowner to diagnose this. It could be explained to you, you could buy a meter and perform the tests with relative ease but, if the problem is outside of your home and the fault of the power company, they won't bother to show up based on your findings (at least none of the POCO's I've worked with.) On the other hand, if a licensed electrician makes the call to them, they will generally come and take a look.
 
  #7  
Old 07-23-04, 06:19 AM
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I agree that your problem sounds like a ground leakage issue. I have read on other electrical related websites that this problem can cause rapid water pipe erosion. You also mentioned that an aluminum wire was connected across your water meter. Iím not sure, but aluminum touching copper might cause electrolysis and rapid erosion. You did not mention anything about your service panel ground wire. There should be a copper wire coming from the breaker panel and terminating near the water meter. Iím not sure, but I doubt that using aluminum wire for a grounding conductor is code compliant anywhere in the US.
 
  #8  
Old 07-26-04, 06:06 AM
Bubbamill
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The house was built in 1984. Copper was used for all wiring with the exception of the feed for the heat pump. The heat pump feed is a huge stranded aluminum cable. The solid wire across the water meter is silver-gray, so I'm assuming it's aluminum. The clamps used don't actually allow the wire to touch the copper pipe. The wire enters a hole in the clamp where it is secured and then the clamp grips the pipe. So the clamp actually makes the connection between the wire and the pipe. It looks to be about a 4 gauge wire and it bridges the meter and then disappears through the basment wall into the soil outside. I'm guessing it travels to the garage where the service panel is located. I haven't pulled the panel cover to see if the aluminum wire is connected there.

Based on all of the responses so far, the question I'm left with is: do I start with an electrician or do I insist that the power company come out and take a look? I don't mind spending the money to make things right, I just want to know that the electrical system is working as designed......
 
  #9  
Old 07-26-04, 09:12 AM
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Essentialy the only responsibility of the Utilty Co. is to maintain the correct voltage-values across the 3 Service-Conductors.

All installation and maintanence of all Grounding-connections at the premises is the responsibilty of the customer.

You mention "Grounding the TV block"--- I suggest you drive an 8-ft. Ground-Rod as a seperate Grounding Electrode for the TV system and "bond" this new GE to the water-service line via a #6 copper Bonding-Jumper.-- You can do this yourself.

The purpose of the Bonding-Jumper is to "short-circuit" any voltage caused by leakage-to-Ground.
 
  #10  
Old 07-26-04, 07:17 PM
CSelectric
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Generally, you will need to call an electrician first. It certainly sounds like you have an objectionable ground current on your water piping. An electrician will be able to determine if it is coming from within your house or entering via the underground water service. If in fact it is coming into your home from outside the house, then the power company will have to be called. There are various things that will cause the phenomena a reference, but the most common is a faulty xonnection at the XO terminal of the power companies transformer. Of course, power companies are generally very slow to admit when they are wrong, so you need the diagnosis of a licensed electrician to make your case to the POCO. If you try to bring them in without an electrician looking at the system, they will almost certainly refuse... and tell you to call an electrician. FWIW, when you call an electrician (and I highly recommend that you do, objectionable ground current is a very serious, potentially very dangerous matter) I would ask if they have experience in the area of power quality, and specifically in tracing ground currents. You may pay more per hour to get someone with that expertise, but I guarantee you'll pay for a lot fewer hours of labor than if you trust it to an electrician with no background in this area.
 
  #11  
Old 07-27-04, 05:39 AM
Bubbamill
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Thanks everyone. I will start the research to find an electrician experienced in diagnosing ground current problems. I'll update this thread once the results are in.

Thanks again!
 
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