Do I need a grounded if my tv is connected to grounded coax?

Originally Posted By: Rich
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Hi,


My home was built in the 20's and the electrical has yet to be upgraded, none of the plugs have ground wires. I just bought a nice television set and I was wondering, since it is connected to the coaxial cable tv (grounded), does this mean the tv is grounded even though the electrical plug it is plugged into has no ground? I'm trying to avoid running a new ground wire for the plug that the tv is plugged into.

Thanks
-Rich


Originally Posted By: jpeck
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If my guess is right, and your cable TV is improperly grounded (like most I see), and your TV came with a two-wire plug, you are better off NOT grounding it.


If you did, you could easily have a potential between the two grounds. That would not be good.

You would be better off with a ground to the TV, but only if done properly, and only if the cable were also properly grounded.

All assuming a two prong plug came on the TV.


--
Jerry Peck
South Florida

Originally Posted By: Greg Fretwell
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Does your TV have a 3 prong plug? If not what are you grounding? Make sure your cable company protection is going to the service ground electrode and put in a whole house protector in the panel.


Originally Posted By: Rich
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Thanks for the responses…


I think that I made a mistake in the post, I said a grounded plug instead of a grounded recepticle.

I haven't received the tv yet but I'm assuming that it will have a 3 prong plug. The cable is grounded to the breaker box. So, if the coax is grounded properly, then I don't need a grounded recepticle?

Thanks a bunch.


Originally Posted By: rzimmerman
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Rich wrote:
Thanks for the responses...

I think that I made a mistake in the post, I said a grounded plug instead of a grounded receptacle.

I haven't received the tv yet but I'm assuming that it will have a 3 prong plug. The cable is grounded to the breaker box. So, if the coax is grounded properly, then I don't need a grounded recepticle?

Thanks a bunch.


I would contact the manufacture of the TV. Home inspectors are not qualified to answer a question such as this. Having spent many years in the electronic industry my advise is call the manufacture.

Also, no not use the shield on the coax as a ground. It is not intended to carry any load. It is a SHIELD no more. Its purpose is to prevent or limit interference. Knowing most cable companies they only put in RG-58 in the house, which has very sparse strands for the shield and wrapped in foil. The buried cable is possible RG-6 or better and rated to direct bury. It has much heaver shielding and sometimes an included ground. DO NOT confuse the two or assume this same cable runs throughout the home.

Rob Z.


Originally Posted By: Greg Fretwell
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I have never seen a consumer TV with a 3 prong plug.


I do have a commercial monitor with one but it was originally part of a PC based educational system with Laser Disk and a mainframe link.


Originally Posted By: jpeck
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rzimmerman wrote:
Home inspectors are not qualified to answer a question such as this.

Also, no not use the shield on the coax as a ground. It is not intended to carry any load.


Rob,

Where are you from?

First, you make a blanket statement that HIs are not qualified to answer this, obviously thinking that you know what everyone else knows, and more. That because you don't know, no other HI does either.

Very bad assumption.

Second, you stated that the shield is not ground (and it is) and that it is not intended to carry any load (it is not). See, apparently your electronic and electrical experience is lacking some basics - a GROUND is NOT INTENDED to carry any load. It is there for safety reasons.

Ever looked at the requirement for grounding cable and phones? The shield on the cable is connected to the metal case on the splitter, coupling, etc., which is REQUIRED to be grounded back to the service ground.

Sounds like you have some very good experience, including thermography, but you are way off base here.

Calling the manufacturer, however, is never a bad idea. It is just not necessary here.


--
Jerry Peck
South Florida

Originally Posted By: rzimmerman
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jpeck wrote:
rzimmerman wrote:
Home inspectors are not qualified to answer a question such as this.

Also, no not use the shield on the coax as a ground. It is not intended to carry any load.


Rob,

Where are you from?

First, you make a blanket statement that HIs are not qualified to answer this, obviously thinking that you know what everyone else knows, and more. That because you don't know, no other HI does either.

Very bad assumption.

Second, you stated that the shield is not ground (and it is) and that it is not intended to carry any load (it is not). See, apparently your electronic and electrical experience is lacking some basics - a GROUND is NOT INTENDED to carry any load. It is there for safety reasons.

Ever looked at the requirement for grounding cable and phones? The shield on the cable is connected to the metal case on the splitter, coupling, etc., which is REQUIRED to be grounded back to the service ground.

Sounds like you have some very good experience, including thermography, but you are way off base here.

Calling the manufacturer, however, is never a bad idea. It is just not necessary here.


Jerry,
Apologies if I offended anyone.

At first I took offence at your response. Then I sat back to reflect a minute. While my response was not intended to put down others I can see where that could be read into it. It was not an assumption, it was poorly worded.

I believe the remainder of my response is still fine.

Call the manufacture if you have a question concerning their product.

The shield in coax is not designed to carry any load. The ground wire in electrical wire is designed to carry load. It is designed to carry the load away from you in the event of a short. Not all grounds are created equal.

Again, I did not intend on offending anyone on this board. My goal was to give info and provide direction within the media before me.

And since you asked -- I'm from Dallas, Texas ![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)

Rob Z.


Originally Posted By: jpeck
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rzimmerman wrote:
The shield in coax is not designed to carry any load. The ground wire in electrical wire is designed to carry load.


Rob,

Incorrect. The ground is NOT designed to carry a load. It is intended ONLY to provide a path for fault current back to ground, which is not a load.

Quote:
It is designed to carry the load away from you in the event of a short.


And that is what the shield over the co-axial cable is also being used for.

Look back at the coupling, splitters, etc. and see where the ground wire / screw is attached, then use an OHM meter to see if that is connected to the shield of the co-axial cable, you will find that it is. Thus, the coax shield also serves as the ground path from end to end of the coax cable.


--
Jerry Peck
South Florida

Originally Posted By: Greg Fretwell
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Without getting into a deep discussion of signal propagation and noise let me say simply, the braid on a coax should not be carrying current. TV is a fairly modest use of coax but when you get into serious signal transmission protocols you will see they really only ground one end of a coax to avoid carrying any current.


If you ever get near an old 3270 terminal you would see that the coax port is electrically isolated from frame ground but it is solidly connected to the frame at the controller.


As an after thought it makes me wonder how much TV interference is caused by regrounding all of your splitters.


Originally Posted By: rzimmerman
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Rob,


Quote:

Incorrect. The ground is NOT designed to carry a load. It is intended ONLY to provide a path for fault current back to ground, which is not a load.

semantics, but yes I would have missed that question on a test.

Quote:

And that is what the shield over the co-axial cable is also being used for.
.


Still disagreed here so did some research. After 20+ web sited discussing coax cable specifications I found http://coaxial-cable.globalspec.com/LearnMore/Electrical_Electronic_Components/Wires_Cables/Coaxial_Triaxial_Cables. While this does mention the outer shield as a return path for current carried on the center conductor, it does not mention how much current or voltage. Use or trust as a return current path for 120v AC. Not me.

Can we get that beer now ![icon_smile.gif](upload://b6iczyK1ETUUqRUc4PAkX83GF2O.gif)


Originally Posted By: bhendry
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Here’s some interesting statements:


This is from Grounding and Bonding, Volume 2, Michel Mardiguian, 1988.

"Where to ground a cable shield is one of the all-time dilemmas for the electrical or electronic equipment designer or field engineer. The thousands of reports, articles, specifications, math modeling and experiments published on the subject since the early days of telephony would probably amount to an impressive mountain of paper. And yet the classic scenario is that of a field technician with the braided shield end in one hand and a screwdriver in the other, asking desperately where he should ground this shield. Justifiably, he will have a gloomy expectation of getting as many different answers as the number of people he asks."

"Fault protection is an integral part of ground network design. Frequently signal grounds are common with fault protection paths, particularly where the structural elements of the building are involved."

If I just bought a nice TV set - I would want a quality surge suppressor/filter system for it - which will need a grounding path - that would be my issue.

Regards,

Bill


![](upload://6W2YnX4wTESErcMziSzPMju9jcW.gif)


Originally Posted By: rzimmerman
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Bill gets a beer too icon_smile.gif


Originally Posted By: jpeck
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This is being changed and made even clearer in the 2005 NEC.


This is from the 2002 NEC.

820.33 Grounding of Outer Conductive Shield of a Coaxial Cable.
The outer conductive shield of the coaxial cable shall be grounded at the building premises as close to the point of cable entrance or attachment as practicable.

820.40 Cable Grounding.
Where required by 820.33, the shield of the coaxial cable shall be grounded as specified in 820.40(A) through (D).
(A) Grounding Conductor.
(1) Insulation. The grounding conductor shall be insulated and shall be listed as suitable for the purpose.
(2) Material. The grounding conductor shall be copper or other corrosion-resistant conductive material, stranded or solid.
(3) Size. The grounding conductor shall not be smaller than 14 AWG. It shall have a current-carrying capacity approximately equal to that of the outer conductor of the coaxial cable. The grounding conductor shall not be required to exceed 6 AWG.
(4) Length. The grounding conductor shall be as short as practicable. In one- and two-family dwellings, the grounding conductor shall be as short as practicable, not to exceed 6.0 m (20 ft) in length.
Exception: In one- and two-family dwellings where it is not practicable to achieve an overall maximum grounding conductor length of 6.0 m (20 ft), a separate ground as specified in 250.52(A)(5), (6), or (7) shall be used, the grounding conductor shall be grounded to the separate ground in accordance with 250.70, and the separate ground bonded to the power grounding electrode system in accordance with 820.40(D).
(5) Run in Straight Line. The grounding conductor shall be run to the grounding electrode in as straight a line as practicable.
(6) Physical Protection. Where subject to physical damage, the grounding conductor shall be adequately protected. Where the grounding conductor is run in a metal raceway, both ends of the raceway shall be bonded to the grounding conductor or the same terminal or electrode to which the grounding conductor is connected.
(B) Electrode. The grounding conductor shall be connected in accordance with 820.40(B)(1) and (B)(2).
(1) In Buildings or Structures with Grounding Means. To the nearest accessible location on the following:
(1) The building or structure grounding electrode system as covered in 250.50;
(2) The grounded interior metal water piping system, within 1.52 m (5 ft) from its point of entrance to the building, as covered in 250.52;
(3) The power service accessible means external to enclosures as covered in 250.94;
(4) The metallic power service raceway;
(5) The service equipment enclosure;
(6) The grounding electrode conductor or the grounding electrode conductor metal enclosure; or
(7) The grounding conductor or the grounding electrode of a building or structure disconnecting means that is grounded to an electrode as covered in 250.32.
(2) In Buildings or Structures Without Grounding Means. If the building or structure served has no grounding means, as described in 820.40(B)(1):
(1) To any one of the individual electrodes described in 250.52(A)(1), (2), (3), (4); or,
(2) If the building or structure served has no grounding means, as described in 820.40(B)(1) or (B)(2)(1), to an effectively grounded metal structure or to any one of the individual electrodes described in 250.52(A)(5), (6), and (7).
(C) Electrode Connection. Connections to grounding electrodes shall comply with 250.70.
(D) Bonding of Electrodes. A bonding jumper not smaller than 6 AWG copper or equivalent shall be connected between the antenna systems grounding electrode and the power grounding electrode system at the building or structure served where separate electrodes are used.
Exception: At mobile homes as covered in 820.42.
FPN No. 1: See 250.60 for use of air terminals (lightning rods).
FPN No. 2: Bonding together of all separate electrodes limits potential differences between them and between their associated wiring systems.

End result is that the shield MUST BE GROUNDED to the electrical system's system ground.


--
Jerry Peck
South Florida

Originally Posted By: Greg Fretwell
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This is what happens when you have rules made by a committee. 820.40(A)(4)&(5) follow good signal and protection guidelines, then (B) shoots it all to hell by allowing the connnection to be made to a marginal connection by signal standards.


Originally Posted By: jpeck
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Greg Fretwell wrote:
This is what happens when you have rules made by a committee. 820.40(A)(4)&(5) follow good signal and protection guidelines, then (B) shoots it all to hell by allowing the connnection to be made to a marginal connection by signal standards.


(B) is not as complex as it first seems, however, I'll bite - please explain why "(B) shoots it all to hell".


--
Jerry Peck
South Florida

Originally Posted By: Greg Fretwell
This post was automatically imported from our archived forum.



jpeck wrote:
Greg Fretwell wrote:
This is what happens when you have rules made by a committee. 820.40(A)(4)&(5) follow good signal and protection guidelines, then (B) shoots it all to hell by allowing the connnection to be made to a marginal connection by signal standards.


(B) is not as complex as it first seems, however, I'll bite - please explain why "(B) shoots it all to hell".


The short answer?
We started out with a short straight grounding conductor then suddenly it was OK to connect it to the grounding electrode system "To the nearest accessible location" be that a pipe, wire twisted around hell and back or some piece of building steel that might not even be effectively grounded. Did anyone really meg it out?
If we are going to talk about signals and surges we should read the whole book.


Originally Posted By: jpeck
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Greg,


Read it again.

Here it is. I've made it easier to read.

(B) Electrode. The grounding conductor shall be connected in accordance with 820.40(B)(1) and (B)(2).
- (1) In Buildings or Structures with Grounding Means. To the nearest accessible location on the following:
- - (1) The building or structure grounding electrode system as covered in 250.50;
- - - (Jerry's comment: What's wrong with that?)
- - (2) The grounded interior metal water piping system, within 1.52 m (5 ft) from its point of entrance to the building, as covered in 250.52;
- - - (Jerry's note: This just also happens to be the first 5 feet where the water pipe bond should be. What's wrong with that?)
- - (3) The power service accessible means external to enclosures as covered in 250.94;
- - - (Jerry's note: "250.94 An accessible means external to enclosures for connecting intersystem bonding and grounding conductors shall be provided at the service equipment and at the disconnecting means ... ", that is AT the service equipment and main disconnect. What's wrong with that?)
- - (4) The metallic power service raceway;
- - - (Jerry's comment: Which is grounded right there at the service, if it is metal. Again, what is wrong with that?)
- - (5) The service equipment enclosure;
- - - (Jerry's comment: Which is grounded right there at the service. Again, what is wrong with that?)
- - (6) The grounding electrode conductor or the grounding electrode conductor metal enclosure; or
- - - (Jerry's comment: Which is right there at the service. Again, what is wrong with that?)
- - (7) The grounding conductor or the grounding electrode of a building or structure disconnecting means that is grounded to an electrode as covered in 250.32.
- - - (Jerry's comment: 250.32 covers separate buildings. 250.32 Two or More Buildings or Structures Supplied from a Common Service. If done in accordance with that section, what is wrong with that?)

Greg, I think you did not read it past "To the nearest accessible location", did you?

The "nearest accessible location" at something already located at the service equipment is going to be very short, and in no way does that allow the bond to be to "hell and back or some piece of building steel that might not even be effectively grounded".

I think you read it as "To the nearest accessible location" to the cable fitting, which could be on the other side of the house.


--
Jerry Peck
South Florida

Originally Posted By: Greg Fretwell
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The point is this isn’t 60hz noise and surges we are trying to suppress. They wouldn’t be using the “straight and short” langusge if they really meant down a water pipe that may have a half dozen elbows and a water meter jumper on it or a raceway system with any number of RF no-nos in it. When we were grounding computer floors for noise we wanted the straps tight with no bends in them at all and we had sparky wrapping them around the floor posts. (a choke).


Originally Posted By: jpeck
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Greg Fretwell wrote:
The point is this isn't 60hz noise and surges we are trying to suppress.


Actually, it is.

This is for stray voltage, surges, etc., of the 60 hz type, plus any other stray voltages or surges, but mainly for the 60 hz ones. Trying to keep the ground level equal with each other. It does no good to have the cable shield at one ground level and the equipment ground in the cord at another. Hence, leaving the ground out if there is no grounded type cord. If there is, make sure that the cable ground and equipment ground are at the same level. Even no ground (two prong plug) creates problems because the cable shield ground may be different than the bonded-to-ground neutral conductor which is connected to the TV. Now you could have two ground reference levels: a) the neutral conductor on the cord; b) the shield on the cable.

What does the outer part of the coax fitting mount on and connect to? The chassis, for a chassis ground, which is ALSO the equipment ground on grounded equipment. Or should be, anyway.

I used to test, calibrate, and repair oscilloscopes (of the tube type, and then the solid state type (they were coming in as I was going out of it), volt meters, signal generators, and other equipment. I worked in a large defense plant in Standards Lab (after working in Quality Control and R&D Test). There were (if I am counting and remembering correctly) six of us who kept the equipment in the plant calibrated, plus one who mainly kept our stuff calibrated, plus the head guy over all of us in the Standards Lab. This was for a plant with over 500 employees running equipment all over the plant, making electron tubes for radar systems.

If you walked at a brisk walk, it would take about 20 minutes to walk from one side of the plant to the other, and about 15 minutes from the front to the back. That gives an idea of the physical size of the plant, and the area we covered.

But I side-tracked there.

In addition to the coax grounds (on the scopes), the grounds in the cord and plugs, I had to ground strap all the equipment I was worked on to make sure there was no ground loops or other interference on the grounds. We all had to ground strap everything we worked on and calibrated.

Many of the problems we ran into (after we returned the equipment to service) were ground loop problems.

Not only was this bad for measuring and monitoring what the equipment was doing, but ground loops would also create quite shocking conditions for the workers. Many times we would work with Building Maintenance (the electricians, plumbers, carpenters, welders, you-name-it-tradesman) to solve those problems.

Hey, I'm talking like I know this stuff and it's been about 30 years since I did it. Ah, the mind does not forget all, I guess. ![icon_cool.gif](upload://oPnLkqdJc33Dyf2uA3TQwRkfhwd.gif) Maybe there is hope for me after all.


--
Jerry Peck
South Florida