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"Sharing" ground between satellite and OTA/cable?


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23 replies to this topic

#1 OFFLINE   slice1900

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Posted 17 September 2013 - 01:47 PM

I currently have three coax runs to each TV, one for Directv, one for OTA and one for cable. The Directv coax is connected to the receiver (either H20 or H24) and the OTA coax is connected to the H20 or AM21 (for H24) The cable coax is connected to the TV's RF input. The TV and receiver are connected via HDMI. The TVs are Panasonic plasmas and LG plasmas, if that matters.

 

Are the grounds of the three different coax families separate in this situation, or are they sharing a common ground? The reason I ask is that I'm looking into wall plates for the three coaxes, which currently home run directly to where they connect at the TV/receiver.

 

Some wall plates are plastic, or metal using plastic inserts and thus non-conductive between the three coaxial cables. Others are all metal, and as far as I can tell would offer a conductive path between the shields of the three coaxial cables. I would prefer the all-metal solution since it would be more durable, as I'm not impressed with how easily plastic coaxial keystone inserts pop out if you even look them at cross eyed. I don't want to deal with them popping out anytime a TV is rotated around a bit.

 

I want to determine if using the all-metal solution that would appear to share ground is something I should avoid. Of course, if it turns out I'm already sharing grounds due to the Directv/OTA being connected to H20s together, and the cable perhaps also sharing ground from the TV via the HDMI cable then obviously any additional ground sharing doesn't matter.


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#2 OFFLINE   carl6

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Posted 17 September 2013 - 03:17 PM

The grounds should all be the same, there should be no problem using a conductive wall plate (or not).

#3 OFFLINE   slice1900

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Posted 17 September 2013 - 06:34 PM

The grounds should all be the same, there should be no problem using a conductive wall plate (or not).

 

 

"Should" all be the same, yes, but I doubt they are (mostly because my dish and antenna are not grounded, and I don't see a green wire coming/going from the gray box on the outside of the building marked with the cable company's name, either, which I do from the telephone company box right next to it) :)

 

Yes, I should get around to having the dish and antenna grounded, but things have been fine for 8 years so I haven't had any reason to worry too much about it. I have seen a few odd things where the cable is concerned that lead me to suspect it isn't grounded and if not probably ought to be, but when I called them once to ask them to come ground it they assured me they always ground all their installs and wouldn't even send someone out to open the gray box to prove it to me. The dish & antenna are over 100 feet from the service entrance where the grounding rod is (I assume) so they'd probably be grounded to the electrical box of a nearby roof AC unit.

 

But I get what you're saying, if I do get everything properly grounded then they should all be at the same ground potential and thus there should be no reason why they can't share conductive wall plates. I am still curious if the way things are connected now results in them already sharing a ground. I just don't know if having Directv & OTA connected to an H20 grounds the shield of each coax together (and maybe to the electrical ground, since the H20 of course has a grounded plug) As well as whether the cable coax is grounded by the TV and/or via the HDMI cable to the receiver. I have a super cheap multimeter, maybe I'll try testing the shields of each coax against each other and see if I can learn anything...


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#4 OFFLINE   JosephB

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Posted 17 September 2013 - 10:37 PM

The grounded electrical plug does NOT ground your dish. You should ground it and your OTA antenna separately from the box inside.



#5 OFFLINE   FYRPLG

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Posted 17 September 2013 - 10:48 PM

they should all show common on a multimeter.  You should ground them all outside your home..  This is just a good safety measure for lightning and other Electrical querks that could, but never come up.

Safety FIRST!!!!!!!



#6 OFFLINE   slice1900

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Posted 18 September 2013 - 02:59 AM

I know the electrical plug doesn't ground the dish, but the receivers themselves are obviously grounded. The question is, do the receivers connect the coax shield of the Directv and/or OTA cable to ground or are they isolated?


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#7 OFFLINE   JosephB

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Posted 18 September 2013 - 07:33 AM

I know the electrical plug doesn't ground the dish, but the receivers themselves are obviously grounded. The question is, do the receivers connect the coax shield of the Directv and/or OTA cable to ground or are they isolated?

 

No, they explicitly do not ground the coax (which would ground the dish). The coax/dish must be grounded. The coax and dish are connected, so you can ground the coax at a ground block/splitter at the entrance to your house and that will take care of the dish--no need for a ground out at the dish.

 

I'm not an electrician, but I did stay at a holiday inn last night. I'm pretty sure the reason it doesn't ground through your box is that the ground in your outlets is actually just connected to the neutral in your circuit breaker box. You wouldn't want that to have a path to ground. If something shorted in the box, you would be electrocuted. That may not be exactly right but I'm sure you don't want to separately ground your neutral wire directly to ground outside of the normal electrical system.

 

If that preceding paragraph is wrong, and someone please correct me if it is, I do know that my first one is right. The coax MUST be grounded separately from the ground in the power cord to the box.


Edited by JosephB, 18 September 2013 - 07:38 AM.


#8 OFFLINE   veryoldschool

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Posted 18 September 2013 - 09:00 AM

Ground isn't connected to the neutral, but the neutral is connected to ground.

The older receivers [H20 and earlier] do ground the shield through the case as they have 3 prong plugs.


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#9 OFFLINE   Rich

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Posted 18 September 2013 - 09:34 AM

No, they explicitly do not ground the coax (which would ground the dish). The coax/dish must be grounded. The coax and dish are connected, so you can ground the coax at a ground block/splitter at the entrance to your house and that will take care of the dish--no need for a ground out at the dish.

 

I'm not an electrician, but I did stay at a holiday inn last night. I'm pretty sure the reason it doesn't ground through your box is that the ground in your outlets is actually just connected to the neutral in your circuit breaker box. You wouldn't want that to have a path to ground. If something shorted in the box, you would be electrocuted. That may not be exactly right but I'm sure you don't want to separately ground your neutral wire directly to ground outside of the normal electrical system.

 

If that preceding paragraph is wrong, and someone please correct me if it is, I do know that my first one is right. The coax MUST be grounded separately from the ground in the power cord to the box.

 

I do believe the neutral bar in a panel is directly connected to a ground rod per NEC regs.  I hate ground arguments, tho.

 

Rich



#10 OFFLINE   Rich

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Posted 18 September 2013 - 09:35 AM

Ground isn't connected to the neutral, but the neutral is connected to ground.

The older receivers [H20 and earlier] do ground the shield through the case as they have 3 prong plugs.

 

I think the R10 DVR had a 3 prong plug too.

 

Rich



#11 OFFLINE   Rich

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Posted 18 September 2013 - 09:40 AM

they should all show common on a multimeter.  You should ground them all outside your home..  This is just a good safety measure for lightning and other Electrical querks that could, but never come up.

Safety FIRST!!!!!!!

 

Ground is properly checked with a megger.  You really have to shoot about 500V into the line to get the proper readings.  I watched an electrician check grounds in a new substation a few years ago with a megger and each line rang out with a different result.  A multimeter just doesn't have the power to do the ground checks properly.

 

Rich



#12 OFFLINE   slice1900

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Posted 18 September 2013 - 02:49 PM

Since the H20 has a metal case with 120v feeding an internal power supply, I would assume it would have to be grounded to achieve UL listing. When I opened one up and took a quick peek I couldn't find any obvious grounding. No green wires screwed to the case, but that could be hidden from view since I didn't completely disassemble it to pull the power supply board and main board (maybe when I have time I'll do it on one of my dead -600s)

 

But I have no reason to doubt VOS on this, I'm sure he's correct. The shield of the satellite coax and of the antenna coax are grounded to that metal case, and therefore to each other. For me over a dozen times to four different electrical panels :)

 

I did a little checking via google, and it sounds as though the coax shield on the RF input is grounded on many if not all models of Panasonic plasma. So my cable is likely grounded through most if not all of my TVs.

 

Based on this I will not worry about sharing ground if I decide to go with the all metal wall plates as I already am sharing ground.

 

Thanks for the help and info, everyone!


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#13 OFFLINE   gov

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Posted 18 September 2013 - 03:02 PM

Last time I had cable, (1993) cable ground and electrical ground in the building were not the same.  Had to have an isolator on the coax or I had rolling 'bars' on the TV picture.

 

I can well imagine back then it was a common problem as Radio Shack carried the isolator.  As for now, I would be surprised if it was more common then than now, but I would also be surprised if the ground problem(s) have been fixed on all cables systems everywhere.

 

Be careful.

 

Homeowners have been known to rewire plugins with absolutely no regard for the wire color.



#14 OFFLINE   JosephB

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Posted 18 September 2013 - 03:41 PM

Last time I had cable, (1993) cable ground and electrical ground in the building were not the same.  Had to have an isolator on the coax or I had rolling 'bars' on the TV picture.

 

I can well imagine back then it was a common problem as Radio Shack carried the isolator.  As for now, I would be surprised if it was more common then than now, but I would also be surprised if the ground problem(s) have been fixed on all cables systems everywhere.

 

Be careful.

 

Homeowners have been known to rewire plugins with absolutely no regard for the wire color.

 

CATV and Satellites can share the same ground. As a matter of fact, right now my cable (installed by Charter) and my DirecTV are both grounded to the same rod that grounds my electrical service entrance.



#15 OFFLINE   Racer88

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Posted 18 September 2013 - 06:07 PM

Umm no Earth Ground testers are used to test grounding

Megohm meters(meggers) are used to test insulation resistance....(hence the proper name "Insulation Testers")

 

All coaxial cable shields should/need to be BONDED to the electrical service entrance ground rod at the point they enter a structure, or at least as close as possible.


Edited by Racer88, 18 September 2013 - 06:17 PM.


#16 OFFLINE   slice1900

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Posted 18 September 2013 - 09:55 PM

Last time I had cable, (1993) cable ground and electrical ground in the building were not the same.  Had to have an isolator on the coax or I had rolling 'bars' on the TV picture.

 

I can well imagine back then it was a common problem as Radio Shack carried the isolator.  As for now, I would be surprised if it was more common then than now, but I would also be surprised if the ground problem(s) have been fixed on all cables systems everywhere.

 

Be careful.

 

Homeowners have been known to rewire plugins with absolutely no regard for the wire color.

 

 

I remember seeing those isolators in the past. I assume all they are is effectively a cable that has the continuity of the shield interrupted? If so, I guess you could make your own by making a cable where you strip the shield completely off on one end before you fit & compress the connector? Or is there more to them?

 

Seems as though it might not be a bad idea to do that with your CATV connection, since you don't always control whether or how it is grounded. If the connection is hidden inside one of those gray boxes with a security key utilities like to install, you may not even know if it is grounded. It might be fine until they change something one day.


SL5, PI-6S, SA-6AL 3xSWM16, 21 H20-100, 1 H20-600, 7 H24-700/AM21


#17 OFFLINE   veryoldschool

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Posted 18 September 2013 - 10:30 PM

I remember seeing those isolators in the past. I assume all they are is effectively a cable that has the continuity of the shield interrupted? If so, I guess you could make your own by making a cable where you strip the shield completely off on one end before you fit & compress the connector? Or is there more to them?

 

Seems as though it might not be a bad idea to do that with your CATV connection, since you don't always control whether or how it is grounded. If the connection is hidden inside one of those gray boxes with a security key utilities like to install, you may not even know if it is grounded. It might be fine until they change something one day.

DC block, with the shield open.

CATV is know to need these coming into the home.

1) they use 60 volts AC to power their line equipment.

2) their cable run for miles parallel to the power lines.

Old TVs always seemed to have hum bars without a DC block.


A.K.A VOS

#18 OFFLINE   slice1900

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Posted 19 September 2013 - 01:43 AM

DC block, with the shield open.

CATV is know to need these coming into the home.

1) they use 60 volts AC to power their line equipment.

2) their cable run for miles parallel to the power lines.

Old TVs always seemed to have hum bars without a DC block.

 

 

Maybe I'll make up a small open shield cable segment and add that and a DC blocker to my incoming cable line before it connects to anything and see if it cleans up the weird problems I occasionally see that have made me think it isn't properly grounded. Can't hurt, and at least I will no longer have to care whether it is grounded at the building entrance or not.


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#19 OFFLINE   veryoldschool

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Posted 19 September 2013 - 05:46 AM

Maybe I'll make up a small open shield cable segment and add that and a DC blocker to my incoming cable line before it connects to anything and see if it cleans up the weird problems I occasionally see that have made me think it isn't properly grounded. Can't hurt, and at least I will no longer have to care whether it is grounded at the building entrance or not.

an "open shield" must still pass RF.

DC blocks are what you want.


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#20 OFFLINE   slice1900

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Posted 19 September 2013 - 09:24 AM

Wouldn't you want both? The DC block in case the cable company is sending voltage down to the cable center, the open shield segment in case there is some voltage coming down the cable shield due to possibly not being grounded properly at the building entrance? Then you'd be protected from anything they might be doing wrong.

 

For the open shield segment I'm not talking about cutting away the shielding in the middle of the cable and causing RF problems (I think that's what you're referring to?) I was talking about doing this on the end of the cable when you install a connector. Simply cut away a bit more of the shield & braiding that would normally make contact with the connector, then add a layer or two of electrical tape over the cut. When you push on the connector and compress it, it will only contact diaelectric, tape and jacket, leaving an open circuit for the shield since there will be no conductive path to the connector on this end. You add the DC blocker onto the end of that, then attach to your amps, splitters or whatever for distribution.

 

That should accomplish the exact same thing as a 'cable isolator', shouldn't it?


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