Yet Another Grounding Question

[mjstraw]

Dish500 on roof of detached garage using Commdeck mount. RG6 dual with messenger runs thru garage inerior, then underground in conduit 20ft to the house, then about 30ft inside house to receivers.

Messenger conductor connected to dish ground. Grounding blocks at entrance to house (conduit comes up out of ground into junction box w/ ground blocks then into house). Messenger connected to grounding blocks.

Coax entrance to house is on opposite corner of house from primary utility entrance (of course . Number 10 solid conductor ground wire runs from grounding blocks, along with coax (now without messenger) thru the interior of the house and connects to the common utility ground conductor near the electrical entrance panel.

My questions (finally!) are:

Should I do grounding blocks where the cable exits the garage? If so, where would you connect them to ground?

Should I reroute the house grounding cable around the exterior of the house instead of running it inside?

Mark

 

[Todd Humphrey]

My comments are based on the NEC. Your local codes may be different.

The coax ground wire is permitted to run through the structure. The ground wire should be as short as possible. If running the ground wire through the structure results in the ground wire being shorter than running it around the house, that is better. The real issue is the length of the ground wire. It should be less than 20 feet. I doubt it is less than 20 feet. Not a big deal because, the cables that run from the conduit going through the structure to reach the house coaxes POE, has two POE itself.

Think of your cable run in reverse. A cable that goes from one side of the home to another, with both ends ending on the exterior, has two POE's. As long as one end is grounded to code, you are fine.

I would install a ground block at the point where the satellite cables finally connect to the home run wires. You need to ground the cables pre-wired as well as the ones you installed. That 10 awg you ran through the house, is actually only going to serve as a mast ground and as a secondary ground for the coax. That mast ground has no length limitations.

Technically you should have the coaxes ground on the garage, if they run through the structure. if the garage was served by a seperate service panel, there would be other issues to consider. If you cannot get a ground on the garage, I would not worry about it, unless you are in a HEAVY lightning area. If that were the case your local codes would not be the NEC code.

Another thing to keep in mind is, we have to ground all cables, not just the satellite cables. When we run satellite cables down the outside of the home to the pre-wired POE. We are not grounding the cables from the dish to the ground block, we are grounding the coaxes from the ground block that run into the home.

Example:
If you installed a 2x4 switch with two satellite cables from the dish and four cables running to receivers, would you use a double ground block, or a quad ground block (or two-doubles)?

You do not need to ground the two satellite cables, you need to ground the four cables entering the building. If those cables are quad shield, your ground must be able to carry as much current as those four quad shield coaxes can conduct. Would 10 AWG meet that criteria??
I have no idea because there are ZERO specs on what level of current a coax cable can safely conduct. IMO, This is the single largest unknown that the NEC dumps on us.

 

[mjstraw]

The coax ground wire is permitted to run through the structure. The ground wire should be as short as possible. If running the ground wire through the structure results in the ground wire being shorter than running it around the house, that is better. The real issue is the length of the ground wire. It should be less than 20 feet. I doubt it is less than 20 feet. Not a big deal because, the cables that run from the conduit going through the structure to reach the house coaxes POE, has two POE itself.

Think of your cable run in reverse. A cable that goes from one side of the home to another, with both ends ending on the exterior, has two POE's. As long as one end is grounded to code, you are fine.

But both ends don't end on the exterior - one end terminates at my MDF and is then cross-connected to a station/prewire cable up to the receiver location.

And yes, it's definitely longer than 20 feet.

I would install a ground block at the point where the satellite cables finally connect to the home run wires. You need to ground the cables pre-wired as well as the ones you installed. That 10 awg you ran through the house, is actually only going to serve as a mast ground and as a secondary ground for the coax. That mast ground has no length limitations.

Actually, I'm using ground blocks already at the MDF as a poor-man's patch panel. The MDF is next to the primary utility entrance so grounding them to the common ground would be no problem.

Back where the satellite cables enter the house, I've got Cable Innovations surge suppressors instead of ground blocks. I hope the #10 provides them with sufficient ground to function properly.

Technically you should have the coaxes ground on the garage, if they run through the structure. if the garage was served by a seperate service panel, there would be other issues to consider. If you cannot get a ground on the garage, I would not worry about it, unless you are in a HEAVY lightning area. If that were the case your local codes would not be the NEC code.

Not a heavy lighting area. The cables do have two POEs to the garage - one near the mast going down thru the roof, the other leaving on it's way to the house.

If I add another ground point where they leave to go to the house, what should I ground it to? I thought the over-riding concern was to have a common grounding point so you didn't end up with ground potential difference problems?

The garage has a 100amp subfeed panel from the house service. Gound and neutral are isolated as they should be. NEC allows for an optional ground rod (which I have) at the garage connected to the grounding conductor/buss. Could I use this for a coax grounding point?

I could also bring a ground conductor back thru the conduit from the house entry ground blocks (surge suppressors) and connect it to the garage ground rod.

But now I'm starting to see lots of ground loops, which might not be a good thing.

Another thing to keep in mind is, we have to ground all cables, not just the satellite cables. When we run satellite cables down the outside of the home to the pre-wired POE. We are not grounding the cables from the dish to the ground block, we are grounding the coaxes from the ground block that run into the home.

Example:
If you installed a 2x4 switch with two satellite cables from the dish and four cables running to receivers, would you use a double ground block, or a quad ground block (or two-doubles)?

You do not need to ground the two satellite cables, you need to ground the four cables entering the building. If those cables are quad shield, your ground must be able to carry as much current as those four quad shield coaxes can conduct. Would 10 AWG meet that criteria??
I have no idea because there are ZERO specs on what level of current a coax cable can safely conduct. IMO, This is the single largest unknown that the NEC dumps on us.

Interesting perspective on what is really being grounded. I'll have to "ponder" that for a while.

Mark

 

[bhelms]

I'm no expert, nor a licensed electrician, but this is a situation where more is not necessarily better. IOW, having multiple grounds actually creates another hazard that can't be ignored, that associated with "ground loops". The code requires that all grounds be tied back to the building's central ground, the one at the power entrance, and it's for that reason. So even if you have separate entrances for the house and garage, for the antenna grounding purposes, they need to be bonded together. Please correct me if I'm wrong on that.

Also - solid copper wire, as heavy and short as possible is preferrable to reduce resistance to ground. However, equally important is low inductance to ground, and that's accomplished by keeping runs as straight as possible avoiding any loops. Broad flat conductors (not commonly available to the homeowner) are also preferred for lightning grounds as those have lower inductance vs. standard round copper wire grounds.

In actuality, it's highly unlikely that any ground you install will provide even a modicum of protection from a direct strike. But a code-conforming ground will be necessary to protect you from a refusal of your insurance company to cover lightning-related damages! Solid grounding will however protect your equipment from routine static build-up, and might even be enough to protect your house and equipment from damage from induced emf caused by a nearby strike...

 

[mjstraw]

In actuality, it's highly unlikely that any ground you install will provide even a modicum of protection from a direct strike. But a code-conforming ground will be necessary to protect you from a refusal of your insurance company to cover lightning-related damages! Solid grounding will however protect your equipment from routine static build-up, and might even be enough to protect your house and equipment from damage from induced emf caused by a nearby strike...

Shouldn't using the Cable Innovations units instead of passive grounding blocks help?

Mark

 

[Todd Humphrey]

Those surge suppressors are ground blocks. The 10 Awg should be fine. Those units will never come into play unless you get a VERY close lightning strike, OR if the receivers send high voltage out the coax.

The garage sub-panel is a valid ground. There should be a large (2 to 6 Awg) copper ground wire between the main service panel and the garage. That makes the garage ground rod, sub panel and the home ground rod and panel one big ground system. You can ground anywhere on that system. If the garage is serviced from a different service panel (usually means two meters), then you would need to be careful.

 

[dennispap]

Those surge suppressors are ground blocks. The 10 Awg should be fine. Those units will never come into play unless you get a VERY close lightning strike, OR if the receivers send high voltage out the coax.

The garage sub-panel is a valid ground. There should be a large (2 to 6 Awg) copper ground wire between the main service panel and the garage. That makes the garage ground rod, sub panel and the home ground rod and panel one big ground system. You can ground anywhere on that system. If the garage is serviced from a different service panel (usually means two meters), then you would need to be careful.

Thanks

 

[Bijou Media]

Those surge suppressors are ground blocks. The 10 Awg should be fine. Those units will never come into play unless you get a VERY close lightning strike, OR if the receivers send high voltage out the coax.

The garage sub-panel is a valid ground. There should be a large (2 to 6 Awg) copper ground wire between the main service panel and the garage. That makes the garage ground rod, sub panel and the home ground rod and panel one big ground system. You can ground anywhere on that system. If the garage is serviced from a different service panel (usually means two meters), then you would need to be careful.

Sub Panels use a 4 wire that goes back to the main panel. These panels do not use a ground rod because they are bonded via the 4 wire going back to the main panel. This is assuming that it is wired properly.

 

[mjstraw]

Yes, sub-panels require separate, unbonded ground and neutral.

The NEC also permits an optional ground rod(s) when the sub-panel is in a detached structure.

Mark