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Old 04-18-2013, 07:52 PM   #1
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connecting ground bars between two houses


I do structured cabling for datacenters and so I'm out of my depth with regard to what NEC requires in this scenario.

I have some ethernet and satellite dish coax connections running in underground PVC conduit between two houses. I have a ground loop issue as evidenced by small voltage between the coax shield and the ground on the house where the satellite is not mounted. The satellite is properly grounded on the other house, no ground loop detected there.

I'm told by some colleagues at work that the solution is to connect the main ground bus at the service panel of each house together. Is this correct? I will hire a licensed resi electrician to make the actual connections, but I was going to pull the wire myself before he arrives, since I need to pull some more low voltage stuff anyway. Want to make sure I'm ordering the right wire. (6-AWG solid copper w/ green PVC insulation?)

It seems like if there were ever an issue with the ground on one house, the current for the entire service could flow through this new ground wire to the ground on the other house. Seems like that would be a bad thing with 6-AWG copper, but I don't have enough room in the conduit for a very large ground wire. Is this even a valid concern? (I don't know what service I have on each house, but both breaker boxes have 270 amps worth of breakers installed, with all slots full.)

Thanks!

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Old 04-18-2013, 09:19 PM   #2
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connecting ground bars between two houses


Adding up the breakers means nothing.
Does the power to house #2 come from house #1?

You can not connect the ground from one house to the other.

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Old 04-19-2013, 12:01 AM   #3
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connecting ground bars between two houses


Nope, house #1 and house #2 each have their own independent service.

If I can't connect the ground of each house, any idea how I resolve the ground loop?
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Old 04-19-2013, 01:05 AM   #4
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Nope, house #1 and house #2 each have their own independent service.

If I can't connect the ground of each house, any idea how I resolve the ground loop?
For the computer network, I'd probably switch to using fiber-optic. It isn't conductive so it doesn't care about grounding.

For the coax, an isolation transformer should work, unless you need to pass DC voltage? Verify that the AC and DC voltages between the two sides of the transformer are minimal.... hopefully less than a volt or so, and don't hold both sides at the same time....

Disclaimer: I'm probably not qualified in this area, though I do have an electrical engineering degree....
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Old 04-19-2013, 01:49 AM   #5
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For the coax, an isolation transformer should work, unless you need to pass DC voltage? Verify that the AC and DC voltages between the two sides of the transformer are minimal.... hopefully less than a volt or so, and don't hold both sides at the same time....
Isolation transformer was one option I'd dismissed, because dishnet sends voltage and control signals up the coax to the LNB, neither of which are passed apparently with CATV isolation transformers. Probably one could be designed to do what is required here, and that would be a great option, but damned if I can find one for sale anywhere.
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Old 04-19-2013, 03:09 AM   #6
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connecting ground bars between two houses


You can (in fact, may be required to) bond the signal grounds to the panel grounding bus at each house. That should fix it.
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Old 04-19-2013, 08:34 AM   #7
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connecting ground bars between two houses


So you share cable with your neighbor? That's a good idea. Do you split the bill or is it a relative or someone close?
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Old 04-19-2013, 08:45 AM   #8
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connecting ground bars between two houses


make sure at BOTH houses the grounds are right ....
ie ....




when the cable hit house #2 use this ..if he does not have ground rod at that location drive 8' rod in and ground with #6 cooper

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Old 04-19-2013, 02:07 PM   #9
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So you share cable with your neighbor? That's a good idea. Do you split the bill or is it a relative or someone close?
I actually own both houses. They're on the same property, but they have separate electrical services. Nothing illegal going on here, with the possible exception of electrical code violations if I don't get this hooked up correctly!
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Old 04-19-2013, 06:16 PM   #10
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connecting ground bars between two houses


Put in a proper grounding electrode system for each house (includes two 8' ground rods at least 6 feet apart with #6 grounding electrode conductor going to the respective panel).

Interconnect all of the audio equipment and video equipment with a #14 conductor daisy chaining from one piece to the next. This wire may be attached to the shell of an RCA style jack (you fashion an appropriate friction fit sleeve) or bonded to the chassis using an appropriate screw or lug. This ground wire may go through the conduit that carries the audio, video, and RF cables. Connect the far end of this wire to any known ground, a GEC is the best choice.

Some of the pieces of equipment will be grounded to the respective electrical system which powers them, via equipment grounding conductors in their power cords and in the respective electrical system. Ignore this fact.

Note that the maximum GEC size required for ground rods is #6 regardless of the service amperage.
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Old 04-19-2013, 06:31 PM   #11
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connecting ground bars between two houses


You need to bond the COAX wire to the GEC at the second structure.
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Old 04-20-2013, 12:32 PM   #12
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connecting ground bars between two houses


Is the second panel fed from the primary service entrance? If that is so the neutral should be connected to ground at the service entrance, but the neutral should not be grounded at the downstream box. The box should be grounded, but the neutral should not. See NEC Article 384-27. It states; The terminal bar shall be bonded to the cabinet or panelboard frame and shall not be connected to the neutral bar in other than service equipment. Service equipment is the main service entrance.
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Old 04-21-2013, 01:58 AM   #13
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connecting ground bars between two houses


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You need to bond the COAX wire to the GEC at the second structure.
So I agree this should fix the ground loop. But what happens if the service at the first structure experiences an open neutral fault? And what happens if the two structures are on separate transformers? Bad mojo for the tiny coax shield right??? (Because in either case the coax shield provides a path between the neutral side between the two services.)

This seems like a very difficult problem to solve correctly.
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Old 04-21-2013, 02:00 AM   #14
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Is the second panel fed from the primary service entrance?
As stated above, there are two separate services. Only one panel in each house.
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Old 04-21-2013, 02:51 AM   #15
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connecting ground bars between two houses


Would there be any harm in connecting the ground rods from each house together with buried bare copper wire? (Separate connection on each ground rod from the service connection.)

It seems to me the same electrical connection exists from house to house with metal city water pipe systems. Some areas even require a bonding jumper across the water meter and this completes the connection between homes (if rubber grommets were isolating the meter from the main).

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