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Grounding dish or ground SWM-16s?


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#1 OFFLINE   slice1900

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Posted 02 March 2013 - 02:28 PM

I'm still waiting for the snow on the north side of the roof to melt to get someone out to check my dish's aim and the LNB, and one of the things I'm also going to have him check while he's up there is if my dish (and OTA antenna) is properly grounded. If it is I'll leave it alone, my question is what to do if it turns out I'm not. He may know exactly what needs to be done, and if he's sure of himself I'm not going to tell him how to do his job, but I think the more information you can be armed with to ask the right questions the better off you are.

If I'm not grounded, would it better to ground the dish/antenna or ground at the first connection point inside? It may not be easily feasible to ground outside, because this is a 10,000 sq ft commercial building and the service entrance is 100 feet away. I have about 25 feet of coax between my dish and splitters, so if I ground inside it would be fairly close to the dish. I know Directv requires its installers to ground the dish, but I don't care what they say so much as what those here who have a lot of experience and expertise in this area would do in their own homes. The only thing I know for sure is that I should not ground both unless I'm 100% certain they're going to the same spot on the same ground, as a ground loop can be worse than no ground at all. I just don't understand Directv's logic, since they seem to insist that you need to ground the dish, and you don't want ground loops, so what is the green screw on the SWM-16 for? :confused: I guess there are some cases where the dish and SWM-16 are in close proximity outside the house and can be connected to a common ground wire?

I did some Google "research" on this and there seem to be conflicting opinions, especially with regard to OTA antennas (mine has no rotator, so it won't have the massive static buildups those apparently often have) Some people say it is a must to ground a dish or antenna with a grounding block within a foot of where the coax starts. Others say doing so is at best unnecessary and at worst can actually create a more attractive path for lightning, and you should just ground at the first connection point. Thus I'd want to ground the splitters feeding the SWM-16s (if I can assure myself they're conductive) or using the green grounding screw on the SWM-16s. Or would it be preferable to use a grounding block before the splitters?

The way I look at it, if you take a direct lightning hit, you're screwed whether you're grounded or not, so direct lightning strikes are an irrelevant concern to me as far as grounding goes. I certainly don't want to make a direct strike more likely, but mainly I'm concerned with reducing the risk of problems that could damage equipment unnecessarily or cause hard to trace flakiness. I need to be grounded somewhere to avoid static discharges building up for whatever reason, and better survive indirect strikes. I know a lot of people are running ungrounded, whether they know it or not, but I figure it is cheap insurance. I just don't know whether the best insurance is grounding inside or grounding outside. If there's little difference I'd ground inside just so I can see it and know it is there :)

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#2 OFFLINE   Stuart Sweet

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Posted 02 March 2013 - 02:32 PM

Ground the dish. You are right,,, get struck by lightning and you are toast, but proper grounding can protect you from lesser calamities. As for grounding the SWM I am not sure it is necessary if the dish is properly grounded. The SWMs and the splitters can be grounded at the attachment points but personally I think that might be overkill.
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#3 OFFLINE   veryoldschool

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Posted 02 March 2013 - 02:47 PM

"I'd guess" every reply to this thread will be different. :lol:

I'd want the ground to be "before" entering the building.
Should it discharge a large amount, I'd like it to stay outside [as much as it will].

Now, ground loops from grounding the dish and the SWiM I don't think will be a "loop". I just don't see where the voltage will cause a loop with the dish & the SWiM grounded. "A belt & suspenders" seems like all this would be.
If my SWiM was mounted before entering the building, I'd use it [myself] for the ground, where the messenger from the dish would attach and then to ground, thus not needing a ground block.
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#4 OFFLINE   samrs

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Posted 02 March 2013 - 09:32 PM

On commercial buildings we don't have to ground at the service entrance. The buildings metal frame can be used for a ground bond instead. If there is a suitable location on the roof to mount a ground block prior to your splitters then I would put it there. Distance from the dish is immaterial. Distance from the ground block to the ground bond must be less than 18 feet.

Directv spent a lot of time and money getting their switches and splitters UL listed so they could be used as grounds. A ground wire from the dish can be attached and a ground wire to the ground bond.

Personally I dont like using my SWM16 for a ground. It is mounted outside but there is a ground block prior to the switch. It's been my experience that switches don't do well when static discharges run through them. ;)
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#5 OFFLINE   slice1900

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Posted 02 March 2013 - 09:39 PM

"I'd guess" every reply to this thread will be different. :lol:

I'd want the ground to be "before" entering the building.
Should it discharge a large amount, I'd like it to stay outside [as much as it will].

Now, ground loops from grounding the dish and the SWiM I don't think will be a "loop". I just don't see where the voltage will cause a loop with the dish & the SWiM grounded. "A belt & suspenders" seems like all this would be.
If my SWiM was mounted before entering the building, I'd use it [myself] for the ground, where the messenger from the dish would attach and then to ground, thus not needing a ground block.



My understanding is that a ground loop could arise if the dish and SWM weren't grounded to the same ground. If one thing is grounded directly to the electrical service ground that's bonded to the grounding rod, and the other is grounded to something you might assume is bonded to the house ground but for some reason isn't, like a steel structural beam, rebar in the foundation, or a cold water pipe, the different potential of the two grounds would cause a current between the dish and SWM. Probably only a tiny one that wouldn't cause any trouble, until someday an accident or bad luck causes a big discharge to one of those grounds, some of which may take the path between dish and SWM to the other ground! :eek2:

In my case, since this is a commercial building which has four separate electric meters and four separate water meters, I'm not really 100% sure if they all share a common ground. They should, they probably do, but I probably shouldn't count on it. The dish is pretty much 25' straight up from the SWM, so if they were both grounded to something bonded to the electrical ground I'd be fine, since being in the same location both would be related to the same meter and thus be a common ground. But perhaps the dish is grounded to a steel beam in the attic. If so, short of paying an electrician a lot of money to investigate, I'd have no way of knowing whether that ground is bonded to the same ground as the electrical ground, or the fire sprinkler ground.

This is why you're supposed to only ever have one house ground, and if you need a second grounding rod added elsewhere for some reason, it has to be bonded to the main house ground in a particular way to avoid exactly this sort of issue.

#6 OFFLINE   slice1900

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Posted 02 March 2013 - 09:45 PM

On commercial buildings we don't have to ground at the service entrance. The buildings metal frame can be used for a ground bond instead. If there is a suitable location on the roof to mount a ground block prior to your splitters then I would put it there. Distance from the dish is immaterial. Distance from the ground block to the ground bond must be less than 18 feet.

Directv spent a lot of time and money getting their switches and splitters UL listed so they could be used as grounds. A ground wire from the dish can be attached and a ground wire to the ground bond.

Personally I dont like using my SWM16 for a ground. It is mounted outside but there is a ground block prior to the switch. It's been my experience that switches don't do well when static discharges run through them. ;)



Thanks for the post. I was guessing if they did it at all when they originally installed it, they'd have to have grounded it in the attic, and the steel support beams are the only thing I can think of they could use up there. I'll make sure the guy I have out checks there if it isn't grounded on the roof, or maybe I'll go poking around the attic myself if I get a chance.

#7 OFFLINE   veryoldschool

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Posted 02 March 2013 - 10:46 PM

My understanding is that a ground loop could arise if the dish and SWM weren't grounded to the same ground. If one thing is grounded directly to the electrical service ground that's bonded to the grounding rod, and the other is grounded to something you might assume is bonded to the house ground but for some reason isn't, like a steel structural beam, rebar in the foundation, or a cold water pipe, the different potential of the two grounds would cause a current between the dish and SWM. Probably only a tiny one that wouldn't cause any trouble, until someday an accident or bad luck causes a big discharge to one of those grounds, some of which may take the path between dish and SWM to the other ground! :eek2:

In my case, since this is a commercial building which has four separate electric meters and four separate water meters, I'm not really 100% sure if they all share a common ground. They should, they probably do, but I probably shouldn't count on it. The dish is pretty much 25' straight up from the SWM, so if they were both grounded to something bonded to the electrical ground I'd be fine, since being in the same location both would be related to the same meter and thus be a common ground. But perhaps the dish is grounded to a steel beam in the attic. If so, short of paying an electrician a lot of money to investigate, I'd have no way of knowing whether that ground is bonded to the same ground as the electrical ground, or the fire sprinkler ground.

This is why you're supposed to only ever have one house ground, and if you need a second grounding rod added elsewhere for some reason, it has to be bonded to the main house ground in a particular way to avoid exactly this sort of issue.

The SWiM is already passing current [power] to the dish, so "even if there were" a ground loop, I don't see it causing any problems "in this case".
If you model the circuit, regardless of which ground would be the better ground it shouldn't cause a problem.

If you model the circuit, regardless of which ground would be the better ground it shouldn't cause a problem.
A "bad ground loop" runs through an amp, or between two pieces of equipment, but the LNB to SWiM path just isn't going to have a problem.
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#8 OFFLINE   kymikes

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Posted 03 March 2013 - 07:25 PM

Starting back in the days of the round dish, my initial installation kit had instructions for grounding the dish and also included ground blocks for each coax as it entered the house. When I went to a SWIM LNB, the installer left the 4 coax connections in the arm of the dish 'in case you might need to go to a SWIM16'. When the installer put in the SWIM16, he put new RG6 from the LNB to the SWIM16 and did not use the grounding block for the new coax. I did notice that the SWIM16 does have 4 green grounding screws (1 at each corner). I can't seem to find 'installation instructions' for the SWIM16/dish and was wondering if there is a preferred installation connection to the house ground. I'm guessing from the earlier posts that opinions will vary

#9 OFFLINE   cwtech

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Posted 03 March 2013 - 09:50 PM

as mentioned will vary per every answer, but it is all going to depend on your situation and your wiring, and your grounding options, and were your equipment is placed. sounds like in your case the installer bypassed an outside ground block and ran straight to the swm 16, as long as this is grounded you should be good. If not what is accessable within 25 ft, meter? cold water pipe? as long as it is shorter than 25 ft, and shorter than the shortest cable run from switch to receiver it would pass a qc

#10 OFFLINE   AntAltMike

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Posted 04 March 2013 - 10:39 AM

"The code" has separate requirements for grounding the mast and the coaxes. Many installers ground the mast by having the so-called "messenger wire" coupled to the coax ground block ground wire in the groundblock. There was always some dispute over whether that was permissible or not, but in the last few revisions of the code, further restrictions have been placed regarding how short and direct a path the mast ground wire must follow which makes it even more difficult to satisfy with a single groundwire to grounding electrode system wire.

A ground loop is not a ground fault or interruption. A ground loops does not cause safety problems, but it can cause annoying technical problems at low frequencies. It can introduce low frequency hums in audio circuitry, and put bars on CRT screen that slowly move up the screen.

Coax cables must be grounded as near as possible to the point at which they enter the building, so even though a SWM switch is grounded, it may not satisfy the coax grounding mandate regarding coaxes that have significant distance between the SWM switch and the penetration point.

Strangely, the code does not require the coax outer conductor ground to be outside of the building.

In commercial buildings, cold water pipes can be used for grounding as long as they are substantially exposed and professionally maintained.

#11 OFFLINE   slice1900

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Posted 04 March 2013 - 12:56 PM

"The code" has separate requirements for grounding the mast and the coaxes. Many installers ground the mast by having the so-called "messenger wire" coupled to the coax ground block ground wire in the groundblock. There was always some dispute over whether that was permissible or not, but in the last few revisions of the code, further restrictions have been placed regarding how short and direct a path the mast ground wire must follow which makes it even more difficult to satisfy with a single groundwire to grounding electrode system wire.

A ground loop is not a ground fault or interruption. A ground loops does not cause safety problems, but it can cause annoying technical problems at low frequencies. It can introduce low frequency hums in audio circuitry, and put bars on CRT screen that slowly move up the screen.

Coax cables must be grounded as near as possible to the point at which they enter the building, so even though a SWM switch is grounded, it may not satisfy the coax grounding mandate regarding coaxes that have significant distance between the SWM switch and the penetration point.

Strangely, the code does not require the coax outer conductor ground to be outside of the building.

In commercial buildings, cold water pipes can be used for grounding as long as they are substantially exposed and professionally maintained.



So what is supposed to happen for grounding the mast? Can that grounding wire be run inside the building and grounded to a steel beam, or does it have to stay outside the building? I would also need to ground my antenna mast, can these two "mast" ground wires be combined since they're close by, or should they run separately?

It sounds like in my situation the "proper" grounding would be to have a ground wire connected to the dish mast and one connected to the antenna mast, which run inside the building together or separately, and connect to a steel beam in the attic for building ground (assuming that's kosher running them inside for ground, otherwise who knows where they would go) Also grounded to that same steel beam would be a grounding block for the four coaxes from the dish, plus another grounding block for the one coax coming from the antenna. Both grounding blocks would be located inside the attic as close as is practical to where the cables enter. Does that sound correct?

Does the requirement for grounding the coax as soon as it enters the building hold even if the coax has a grounding block immediately on the other side? If I already had a grounding block there, it would seem silly to have another one immediately on the other side of the roof. What is the reason for requiring the ground inside the building? It's hard to imagine it would make a difference to have a grounding block immediately on the outside of the roof, rather than a few feet further on immediately on the inside? Or for that matter if I'm doing it inside the building anyway, what the difference the ~20 feet would make between grounding it as soon as possible after entering the building and grounding it at the existing cable ends. Guess it depends on the meaning of "significant distance" :lol:

The people who wrote the NEC code must have had a reason to write it this way. What problems are prevented by having the coax grounded inside rather than outside, and immediately rather than eventually? Obviously they know their stuff, I'm not questioning their reasoning just trying to understand it, so I have a better idea of how much time and money I'd want to getting myself grounded exactly per code if I'm not, versus getting grounded "good enough".

#12 OFFLINE   slice1900

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Posted 05 March 2013 - 09:05 PM

Sort of a related question that occurred to me today. What should I do for grounding my old 72.5* dish? Obviously it is no longer in use, and the coax isn't connected to anything. I want to leave it in place because there's always a chance that Directv might launch a new satellite that the 5LNB won't cover. I figure it could be re-aimed and have a different LNB installed, or at worse the mast/mount and coax could be re-used when a new dish/LNB is installed. No reason to toss it when it isn't where anyone can see it.

I guess I'd still want to ground the dish mast and coax shield in the same way they'd be grounded on the 5LNB. What about the copper core of the coax? Should that be grounded in some way rather than just hanging loose connected to nothing? Or is it just fine if it's grounded since any currents short of a lightning strike that are induced in it have nowhere to go anyway?




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