I have a question about wiring. My mother was having problems with her cable TV reception on one particular channel. The cable guy said the problem was with the ground wire. He said the ground was attached to a pipe in the basement and that an electric current was running through the pipe, which caused the interference.
He detached the ground and told her it wasn’t necessary to have the cable grounded. The reception problem was solved.
Before she calls in an electrician–does anyone have any ideas what this might be all about? What would cause current to run through a pipe? Could it be that the house is grounded to the plumbing, and that was causing the interference? And not that the cable guy didn’t know what he was talking about, but why would the cable be grounded in the first place if it’s not necessary?
Thanks. I’m visiting from Knots.
Replies
Code requires that the cable be grounded where it enters the house.
If there was current on the ground wire then there's something wrong with the house wiring (or, just as likely, the "ground" point chosen originally for the cable wasn't a valid ground).
Run the cable ground to the electrical system ground. If the interference returns, contact an electrician.
(Actually, there is another possibility -- could be that the incoming cable is "hot". You could try grounding it to a ground rod driven outside, somewhere away from the electrical stuff. If the interference returns then the cable co needs to fix their sh*t.)
happy?
I'm no electrician, but it has been my experience and understanding that a) electricity should not be flowing through a pipe, even if that pipe serves as part of the ground for the electrical system (unless the "pipe" happens to be conduit, in which case the wiring inside the conduit could be generating electrical noise that might interfere with the cable signal), and b) all electrical components in a house (phone, computer, appliances, fixtures, pumps, heating/cooling equipment, etc.) should be grounded, no matter what the cable guy says. And, while a metal plumbing system is commonly used as the ground for the electrical, it shouldn't be. The plumbing should be grounded, but it shouldn't act as the ground itself...
There are several electricians on the board who can speak with more authority than I, but I don't think they'll disagree with what I've said...
Edited 2/21/2006 1:43 pm by torn
Thanks for the advice.
The wiring in the house is about 35 years old (the house is 80 years old) and I think an electrician should go in and have a look around in any case.
The water pipe is usually the pathway for grounding the meter panel. Sometimes a "Plumber" will replace the water main with plastic which breaks the electrical grounding.
Electricians will install a driven ground rod, but in dry or sandy ground, there is a lot of electrical resistance.
Best grounding is metallic water pipe that has complete continuity to the City's water main.
I am assuming that this is an older house. When grounded outlets started being used it was common practice to run a ground wire from the receptacle to the nearest cold water pipe.
Code no longer allows that. One of the reasons is that plumbers would work on the pipes and disconnect them and get shocked or replace them with plastic and the grounding was lost.
Code does require that the cold water pipe be bonded to the electrical grounding system and if the incoming water pipe is metal and at least 10ft long then it is also used as part of the grounding system. But, in each case the connection need to be made within the 5ft fo where it enters the house.
This problem could also be caused by a problem with an electrical appliance that is connected to te water pipes, electric water heater and dishwasher come to mind.
The cable should be "ground". It is should connect to a protective block which is a small piece of metal with two cable connections and place for a ground wire. It is usually on the outside of the house just before the cabel enters the house or just inside. It shoudl connect to the ground electrode system.
While the problem might be with the cable I would look at the house wiring first. Specially if the house is more than 30 years old.
Start with an electrican. But tell them what the problem is. You want a troule shooter, not one that just wires new houses.
this is helpful... The remodel I'm doing now uses copper pipes for ground and these pipes go into that flexible black plastic that comes from the well. duh! I'll tell them they need to get a troubleshooting electrician in to give them a good ground... 5 feet from where it comes in from the house. Thanks.
Let me clear up something.There are two different things here.A house needs and electrode grounding system.Most common, except for newly constructed homes, consists of a ground rod and connection to the water pipe, IF that water pipe is metallic for at least 10 ft under ground OR TWO ground rods. However, if the water pipe is not metallic outside, but is inside then the water pipe still needs to be "bonded" to the ground electrode system.In either case the connect to the water pipe is made within the first 5ft of where it enters the house.
Hey Bill, here's a related question. My shop (just going up) will have a subpanel and a Ufer ground. The incoming water is PEX and comes from a tee at the wellhead, not from the house. Is there any protocol for grounding the plumbing system when almost none of the piping is metal? The only copper might be the PEX adapters for angle stops at the bathroom sink.
I would have to read the code with a magnifying glass, but I don't think that there is anything that needs to be grounded/bonded in that case.The code also include "items that might become intergized in use". But the copper stubs don't include that.
Yeah, so long as there's no substantial length of metal pipe anywhere, the plumbing doesn't need to be grounded.
If ignorance is bliss why aren't more people
happy?
Grounding/Bonding are 2 totally different items, nobody here has given a correct answer, unfortunately I am on my way out to dinner and do not have the time to answer, go to http://www.electricalknowledge.com, check out the forums on grounding.
Check with the local building department, before you take the advice of somebody who is not qualified to answer your question.
Article 820 of the NEC says that a grounding conductor #14 or larger and insulated, must be connected to the cable shield where it enters the house. The grounding conductor must be connected to the house's electrical system ground (i.e., NOT a separate ground rod.
Call the cable guy back and have him ground the cable according to the NEC. As Bill mentioned, just hooking up to any old water pipe is no longer allowed. Grounding is an important safety feature should electric power lines accidently touch the cable in a storm, or if lightning occurs in the area.
Unfortunately, what you describe is a common problem. The cable shield runs in close proximity to electrical power lines for long distances, and can pick up some induced 60 Hz current. You tie the cable into your house ground, and it shows up as "ground loops" which you see on the screen. I think most of the effects you see is some of the ground loop current flowing through the set-top box and to the TV, thus showing up on the input to the TV.
A common way to fix this and still meet Code is to install an isolation tranformer right before the cable goes into the set-top box. Get two 300 ohm - to - 75 ohm matching transformers ( like http://www.radioshack.com/product/index.jsp?productId=2103912&cp=2032057.2032187.2032188.2032195&parentPage=family ). Hook them up back-to-back (i.e., with the 300 ohm "pigtail" side of the two transformers connected together). That breaks the ground loop and should fix the picture.
Edited 3/5/2006 4:33 am by BarryO
Another solution is a DC blocker such as is used for rooftop TV preamps. Won't totally eliminate the problem but should reduce it by an order of 10 or more.
If ignorance is bliss why aren't more people
happy?
I don't mean to hijack this thread, but I get all kinds of noise in my TV only when it is activley raining outside and then only on a few stations. Could your suggesions help or eliminate the noise or may something else be amiss. I've tried to get my electrician out here to trouble shoot this (even offered to pay him) but he's a busy man.
That's probably just the reduced signal due to the rain. The rain physically blocks the signal from the station and also tends to short out the antenna, so you get less signal and more noise. The weaker the station to begin with (and the farther away), the greater the effect.
If ignorance is bliss why aren't more people
happy?
It could also be a frayed antenna cable, when it rains the moisture will short the wires. I had problems with my cable TV a few years ago after the squirrels chewed on the wire; every time it rained my reception went to heck.
When the cable guy came to install a new line into my house a few years ago he connected a ground lug to the copper line that runs between the breaker box and the water main (it is connected within 5 ft of where it enters the house as someone previously mentioned is now code). The cable guy said that he had seen many computers, TVs and other equipment fried from lightning strikes and other surges through the cable and that it was really important to make sure it was grounded. Maybe you can try to connect the cable ground to a more stable ground connection as others have suggested, but I don't think it is worth the risk of damaging your stuff to leave it ungrounded.