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Guest Message by DevFuse

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Is Your Dish Grounded?


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56 replies to this topic

Poll: Is your dish grounded? (181 member(s) have cast votes)

Is your dish grounded?

  1. No (69 votes [38.12%])

    Percentage of vote: 38.12%

  2. Voted Not sure (7 votes [3.87%])

    Percentage of vote: 3.87%

  3. Earth Ground (55 votes [30.39%])

    Percentage of vote: 30.39%

  4. House Ground (50 votes [27.62%])

    Percentage of vote: 27.62%

Vote

#51 ONLINE   Tom Robertson

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Posted 25 July 2007 - 08:21 PM

Wind blowing across the surface of the dish can build up a fair amount of potential (depending on the actual surface material of course).

And the operation of the LNBs is based on a common ground plane between the LNB and the IRD and the optional switch. Mess with the ground, and things go bad.

You are absolutely correct, all the ground points must be tied together to the same ground via very low resistance connection or loops will occur.

Cheers,
Tom

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#52 OFFLINE   Richard King

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Posted 25 July 2007 - 09:31 PM

Wind blowing across the surface of the dish can build up a fair amount of potential (depending on the actual surface material of course).

Yep. Agree. But, where would that charge dishcharge, er, discharge to? With no direct path to ground the nearest place to discharge to would be the shield of the RG-6 cable (through a spark jump if enough charge should build up) and then to the ground block and to ground through the block. Then again, the theory of grounding the dish is to avoid the buildup of a charge in the first place and, because of the charge, the possibility of attracting a lightning strike. If you think too much about this kind of thing it can drive you crazy. :lol:
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#53 OFFLINE   CableSux

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Posted 25 July 2007 - 10:01 PM

Grounding has always been a contentious issue. Anyone that has read the NEC and spent any time trying to decipher it realizes there are 2 sections, one was written for TV antennas (especially towers the stick 30-40-50 feet into the sky) and the other is CATV (cable) where cable wires cross power lines.

The problem with satellite is, since it doesn't seem to really fall under either, they force installers to use BOTH! They use the TV antenna code for grounding the dish (mast) and the CATV code for grounding the cable.

The reason to ground CATV is 2-fold, 1 to protect against shorts with power lines and 2 to re-reference ground before the cable gets to your equipment. Satellite doesn't need to do either unless you're running cables over/under power lines.

The reason for grounding TV antennas and towers is pretty obvious. If a tower falls over and hits power lines or many times lights are installed on TV towers... they have AC power going to them.. protect against shorts. Anyone that's read the NEC knows they are only worried about grounding the "mast". They aren't worried about the cable, probably because until a few years ago, they only used 300 ohm cable, the flat stuff with no shield. You can't ground that! So... the NEC wants the satellite dish "mast" grounded. Not the dish, the mast.

Ground mast (from one code) + ground coax (from another code) = 2 grounds.

In reality... most satellite dishes are all metal. That means the coax shield (which one code wants grounded) is electrically attached to the rest of the metal dish, to include the "mast". use an ohm meter to verify. So technically, the mast and coax shield are the same point. Logic says ground the coax and you've grounded the "mast". The exception would be those dishes that have a plastic yoke, like the Dish 500. But here's where logic really upsets code-lovers... if the dish, I.E. mast is separated from the LNB, then it's just a piece of metal on the roof... why does it need to be grounded? It's no longer electrically connected to the house. It's not going to fall over onto power lines. It's not going to have yard lights mounted to it. :D

Now the real question is... has anyone, anywhere, ever heard of lightening hitting a satellite dish (grounded or not) or electrocuting anyone because it wasn't grounded? I have seen grounding cause more problems because of improper wiring in houses. But that's for another day. :)
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#54 OFFLINE   Richard King

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Posted 26 July 2007 - 07:21 AM

Well stated Mr. Sux. I have seen a BUD or two get hit by lightning (and does that ever make a mess), but can't say that I have ever seen a pizza dish ever get hit, grounded or not.
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#55 OFFLINE   DogLover

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Posted 26 July 2007 - 07:55 AM

Now the real question is... has anyone, anywhere, ever heard of lightening hitting a satellite dish (grounded or not) or electrocuting anyone because it wasn't grounded? I have seen grounding cause more problems because of improper wiring in houses. But that's for another day. :)


Not the dish, but I have had lightning hit the LNB, or at least close enough to the LNB to fry it and leave scorch marks. (In fact in created a large enough charge in the air to turn on my electric toothbrush. Half asleep on a rainy Saturday morning, that produced a very twilight zone moment as my brain tried to process what happened.) This was probably 10+ years ago when first with D*.

Luckily, I was within whatever warranty period they were offering. They send a replacement LNB right away. Said they would charge me if the returned LNB showed lightning damage rather than just a manufacturers defect. They obviously never looked at the bad LNB, because damage was obvious. They never charged me for replacement.:)
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#56 OFFLINE   CableSux

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Posted 26 July 2007 - 11:51 AM

I agree that grounding a dish provides for reducing the potential of attracting lightening. By the same token, it can't guarantee it won't be hit. Just like the tree in your yard can be hit, and you can bet it's well grounded :) Grounded or not, nothing will protect against a direct hit or a "feeler" from a nearby strike.

The question comes down to, if the purpose of the ground is to reference the dish (mast) to the house/earth ground, then isn't the shielding in the coax, being grounded through your AC outlet sufficient? Technically, yes. BUT... there's always a "but" isn't there? lol BUT, what if the customer only has a two-prong plug (although technically, the return side of the outlet is connected to ground).. or the plug isn't wired correctly. By having the installer install a ground block and ground it to the house/earth ground, we avoid that risk.

Soooo, when you say your LNB was hit, it probably didn't make any difference if it was grounded or not. The metal casing on the LNB is electrically connected to the coax shield, which is electrically connected to the receivers chassis and ground and return side of the AC power cord, which is electrically connected to the house ground, which is connected to the earth ground... :)
.
Joel Munn
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#57 OFFLINE   CableSux

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Posted 27 July 2007 - 05:38 AM

What really bugs me is how strict everyone is about grounding satellite dishes (and their cables) but yet TV antennas and towers (for which NEC 210 was specifically written) are almost never grounded.... and we never hear a peep about it. Someone should start a poll asking everyone if their TV antenna tower is grounded. :)
Joel Munn
SatelliteWorld.com | CableSux.com | Reviews
MySpace: CableSux | I Have A Plan To Destroy America
HughesNet, Hughes Mobile, Starband, iDirect, Viasat, Motosat, DTN, EMNet, GTech, ComLabs, FTA, SBCA Certified (only until Feb 07, Oops! Expired. Oh well) [to be continued]...




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