Connecting Solar System Ground To House's Ground Rods?

[Sunking]

Should he disconnect the array from the rod(s) close to the array and bond them instead to the ground system at the service entrance?

No not at all. Read the documents and think of the panels as a Air Terminal in a LPS.

Draw this picture in your mind. A house like the one pictured in my post with the same kind of Gable or Hip roof say running eat to west, and the AC Service is on the west side of the house. Got that picture so far?

We install Air Terminals (lightning or Franklin rod) at each end of the roof on the peak ends. One on the east, and the other on the west. From each Air Terminal you run a Down Conductor straight down to a ground rod on the east and west side. Then you bond the two Air Terminals together running the bonding cable on the peak of the roof in a straight line fashion. Still with me?

So now we have three ground rods in the dirt. One on the east side connected to the Air Terminal via Down Conductor, one on the west side connected to the Air Terminal via Down Conductor. So basically one conductor because it is bonded together that runs up the west side, runs across the top of the roof to the east side, and goes back down the east side Down conductor.

The third rod is the AC Service ground. We bond it to the LPS ground rod on the east side to complete the required connection and make it safe. This is important thing you must understand. There is only ONE BOND between the Building Ground Electrode System and LPS.

OK how does this apply to solar. Simple just consider the row of panels make up the Air Terminals and conductor that runs across the roof. If you only have one Down Conductor, take it to its own ground rod. Then bond that rod to your AC service ground. Try to keep at least 15 feet between them, Just do not use the AC Service ground rod(s) as a lightning Down Conductor ground rod. They must be bonded together at ONE POINT

So here is why. If you take a direct strike to the panels or high voltage utility lines come into contact with the panels, you have a direct planned path to earth to discharge the lightning current, or a path to clear the utility fault. The other purpose is if your panels or wiring fault, they have a direct planned path (The bond you made between the LPS and service equipment ground back to source equipment to operate a over current protection device. Without that bond you would not have a path except through dirt which is forbidden to use because its resistance is way too high.

[sdold]

Thanks Dereck. What's the reason for bonding the service ground to the east rod, instead of the west rod which is closer? If I read it correctly that is.

What makes this hard for me to grasp is that I would have thought all of the rods would need to be bonded together in the dirt (for a short path) because of the step potential during a nearby strike. It looks like what you described has them bonded together, but through a longer path (across the top of the roof).

[Sunking]

Thanks Dereck. What's the reason for bonding the service ground to the east rod, instead of the west rod which is closer?

LOL I got lost where I put the AC service.

What makes this hard for me to grasp is that I would have thought all of the rods would need to be bonded together in the dirt (for a short path) because of the step potential during a nearby strike. It looks like what you described has them bonded together, but through a longer path (across the top of the roof).

You are right, they are bonded together via roof conductor.

You can bond the two Down Conductors ground rods conductor together in the dirt if you wish, but does not gain you much of anything. What you are missing is the roof bonding conductor is much shorter in length with no bends. That keeps both Air Terminals much closer together in voltage potential difference during a strike. If you only did the dirt route you have 6 hard 90 degree turns, and significantly longer wire length down east side wall, around the house, and then up again to the west side wall. It will end up some 3 to 4 times longer than the direct route on the roof.

Hope that helps you.

[thastinger]

I have 2 grounding rods which are 6 to 8ft (can't remember exactly) apart and connected with 6ga copper. My CC, inverter, disconnect all terminate at one of those rods via 6ga copper. After watching the video, I think I'm attracting a lightning strike via the panels/racking and that I'll feed that strike to the rest of my equipment via the common ground if I leave it hooked up.

[nova]

ok, I follow the layout, let me add another issue - the array is mounted on a metal roof, now how can I protect it?

[sdold]

NFPA 780 is the document you want to follow, not NEC.

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

[Blathering1]

Metal Roof

We had a ~175 panel system installed on a metal roof on a metal building, and TMK it did not have separate grounding installed.

[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.

[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.

[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.

[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]

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.

[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

[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]

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