Connecting Solar System Ground To House's Ground Rods?

[sdold]

Make sure the underground Conduit is rigid metal and not EMT or PVC.

I wouldn't use EMT, but what's wrong with PVC?

[sdold]

Steve how are you running the Coax. Underground or over head?

If underground use a metallic raceway, and use the raceway as your bonding cable. It is permitted to be done that way as it is a pipe, plate, or rod electrode. It will be better than a #6 bare Copper wire. If overhead use the messenger aluminum or steel cable

It's an existing installation using PVC conduit. #6 bare stranded is run alongside the coax in the same conduit. We are going to be replacing the transmitters, antennas and coax, and there was talk that the #6 wasn't necessary since "the ground at the tower is an RF ground and the ground at the cabinet is an AC ground, and they don't need to be connected together." That seemed like a bad idea to me and I am pushing for keeping that #6. NFPA 780 says to bond them together anyway.

These are on the AM broadcast band, the ground rod at the tower is one of those chemical grounds, the ones that you set in a hole with bentonite and fill with something that gets good electrolytical action going, I think.

[gvl]

Permitted but not required from a code POV. From a technical POV gains you nothing unless the Sub-Panel is in a different building.

Understood, right now I'm more concerned if this is just plain wrong and/or dangerous. I think the risk of something bad happening is minimal.

Can you access the rebar? Is so there is no better earth ground than a concrete encased electrode or UFER ground. Every ammunition bunker in the USA uses a UFER ground. FWIW a UFER ground and NEC Concrete Encased Electrode are not quite the same thing, same principle.

Thanks, interesting info. No, at least not without breaking of some concrete at one of the rods.

[Sunking]

You and I understand that EMT is not for U/G installs but some people don't know the code and just think any type of conduit is ok to use. So just saying metallic raceway can be misunderstood by most.

I know, good catch.

[SunEagle]

OK EMT you got me on because I assume they follow code which does not allow EMT underground. PVC well permitted but not metallic

You and I understand that EMT is not for U/G installs but some people don't know the code and just think any type of conduit is ok to use. So just saying metallic raceway can be misunderstood by most.

[Sunking]

Make sure the underground Conduit is rigid metal and not EMT or PVC.

OK EMT you got me on because I assume they follow code which does not allow EMT underground. PVC well permitted but not metallic

[SunEagle]

Steve how are you running the Coax. Underground or over head?

If underground use a metallic raceway, and use the raceway as your bonding cable. It is permitted to be done that way as it is a pipe, plate, or rod electrode. It will be better than a #6 bare Copper wire. If overhead use the messenger aluminum wire.

Make sure the underground Conduit is rigid metal and not EMT or PVC.

[Sunking]

Number 2 sounds pretty good to me! Thanks Dereck, I'm going to go read 810.

Steve how are you running the Coax. Underground or over head?

If underground use a metallic raceway, and use the raceway as your bonding cable. It is permitted to be done that way as it is a pipe, plate, or rod electrode. It will be better than a #6 bare Copper wire. If overhead use the messenger aluminum or steel cable

[Sunking]

There's concrete between them, so burying bonding wire isn't a good option. I should probably look into disconnecting the sub from the old grounding, too bad but I will have to go through drywall to do it properly. Or just live with it because the chances of being killed during my commute to work in an accident are likely higher than a lightning strike near my home.

Can you access the rebar? Is so there is no better earth ground than a concrete encased electrode or UFER ground. Every ammunition bunker in the USA uses a UFER ground. FWIW a UFER ground and NEC Concrete Encased Electrode are not quite the same thing, same principle.

[Sunking]

Slightly OT but is there any danger in having a sub-panel enclosure to be connected to a dedicated grounding rod?

Permitted but not required from a code POV. From a technical POV gains you nothing unless the Sub-Panel is in a different building. If that is the case then only run 3-wires (L1, L2, and N) and treat it like a service bonding the Neutral to ground to establish a new Equipment Grounding Conductor. It must meet the conditions of 250.32

[gvl]

I think your doubt is founded. The two ground rods should be bonded. Without lightning, it probably won't matter, but if you can run some buried copper, it would an improvement.

There's concrete between them, so burying bonding wire isn't a good option. I should probably look into disconnecting the sub from the old grounding, too bad but I will have to go through drywall to do it properly. Or just live with it because the chances of being killed during my commute to work in an accident are likely higher than a lightning strike near my home.

[sensij]

After reading this thread I now have doubts it was done correctly. The only physical connection between the two grounding electrodes is the equipment ground path between the sub and the main (EGC and EMT), there is no additional bonding. Lightning strikes here are rare.

I think your doubt is founded. The two ground rods should be bonded. Without lightning, it probably won't matter, but if you can run some buried copper, it would an improvement.

[gvl]

Slightly OT but is there any danger in having a sub-panel enclosure to be connected to a dedicated grounding rod? The sub is properly fed with 4 wires from the main, and the main has its own grounding rod. I had my service entry relocated and what used to be the main panel became a sub-panel off the new main, and the sub was connected to the original main grounding electrode (which I think is tied to rebar in the foundation). A grounding rod was added at the new service entrance and bonded to the cold water pipe. Both the main and the sub are on the same structure. After reading this thread I now have doubts it was done correctly. The only physical connection between the two grounding electrodes is the equipment ground path between the sub and the main (EGC and EMT), there is no additional bonding. Lightning strikes here are rare.

[sdold]

What path do you choose to equalize lightning fault currents?

1. Through your radio equipment and coax

or

2. Through a #6 AWG bare solid copper conductor buried in the dirt bonded to both radio tower and radio cabinet ground.

Number 2 sounds pretty good to me! Thanks Dereck, I'm going to go read 810.

[Sunking]

I'm trying to find the requirement for bonding multiple ground rods together in NFPA 780, and I'm having trouble.

That is because your thinking it is done at the dirt level which is permitted. What is required and you are over looking is all the aerials and metal objects are bonded together on the roof. Draw this picture in your mind. A simple building like those shown above with a hip roof. Three Air Terminals are used. An Air Terminal at each end, and one in the middle. There are two Down Conductors at each end of the building attached to the Air Terminals at each end. Then you have a Bonding Conductor that runs between the two Air Terminal at the ends along the top of the roof and is bonded to the Air Terminal in the middle of the roof. At the Ground Level each down conductor goes to its own ground rod. Than only one of those ground rods is bonded to the AC service ground electrode system.

I'm working on a job now that has a transmitter in a roadside cabinet with a ground rod under the cabinet, and 100' away is a tower with a chemical ground rod. I assume they need to be bonded, otherwise the coax is the only current path between them during a lightning event. I'm trying to make that case with my superiors, who don't seem to think bonding between the two rods is necessary, but the only thing I see is 3.14.1 which says that all grounding media shall be interconnected. Is this what I'm looking for?

Very good, you understand. Yes that is what 3.14.1 is telling you. It is also what NEC 810 requires you to do.

Answer your boss question with a multiple choice Question with 2 answers?

What path do you choose to equalize lightning fault currents?

1. Through your radio equipment and coax

or

2. Through a #6 AWG bare solid copper conductor buried in the dirt bonded to both radio tower and radio cabinet ground.