Connecting Solar System Ground To House's Ground Rods?

[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.

[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?

[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?

[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.

[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.

[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]

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]

They have to be bonded for a couple of reason, but only bonded at one location, not two, just once.

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?

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

Thanks, I'm looking through it now.

[Sunking]

I think they go to ground rods that are not bonded to the ground rod at the service entrance. Isn't this unsafe, and wouldn't it be safer to either a) bond those rods together, or b) remove the GECs?

They have to be bonded for a couple of reason, but only bonded at one location, not two, just once. NFPA 780 is the document you want to follow, not NEC.

Another good one for free is UL Application Guide which conforms to NEC and 780. Here is a good overview of LPS

[organic farmer]

I did not serve on a sub for 20 years thank God, only 6 and that was 5-1/2 years too long for me.

However those are there to prevent ships and subs from being a target. Any sub or ship has super low resistance to earth which is what lightning is looking for to discharge through. They are called SHIELDS. A Shield is anything like a tower or structure placed high above an area you want to protect under the Cone of Protection. Disney Parks in Orlando are a Master in th eart of Cone of Protection and is the model used in many schools under UL Master Label. It is so good you cannot even see it at the parks unless you know exactly what you are looking for. Airports also use the technique. Picture is worth a thousand words.

I understand completely.

Since we can not simply ignore lightning strikes, it is better to control them and direct the surges in a safe manner where I want them to go.

btw; I have two lightning rod towers up over my solar-panel array, providing their shield effect over the array. But I admit I may be a bit over-board on the topic, living in a Faraday Cage as I do.

[sdold]

No you should not remove the down wires.

I think they go to ground rods that are not bonded to the ground rod at the service entrance. Isn't this unsafe, and wouldn't it be safer to either a) bond those rods together, or b) remove the GECs?

[Sunking]

I served on subs for 20 years. Every sub pier has wooden 'power poles' every 40 foot, no power lines [those are strung underneath the piers],

I did not serve on a sub for 20 years thank God, only 6 and that was 5-1/2 years too long for me.

However those are there to prevent ships and subs from being a target. Any sub or ship has super low resistance to earth which is what lightning is looking for to discharge through. They are called SHIELDS. A Shield is anything like a tower or structure placed high above an area you want to protect under the Cone of Protection. Disney Parks in Orlando are a Master in th eart of Cone of Protection and is the model used in many schools under UL Master Label. It is so good you cannot even see it at the parks unless you know exactly what you are looking for. Airports also use the technique. Picture is worth a thousand words.

[Sunking]

Well consider what lightening rods do on roof tops,

Make you are target and attract lightning.

[Sunking]

Anyways, I wonder if I should remove my 6Ga copper wire from my array to my ground rods, I initially didn't have it but the inspector wanted one there so I put one in. I certainly follow the logic of Mr. Holt because now I have provided a path for the lightning to reach my internal equipment (CC,Inverter etc) from the outside lightning strike source (the array itself). If left ungrounded, the PV array should have the same potential as the building itself, by adding the ground rod, I've given the lightning bolt a target...experts concur?

You guys do know I am a current moderator for Mike, and was an instructor for him on grounding right?

No you should not remove the down wires. Current NEC specifications of allowing the EGC provide the path is a huge blunder sneaked by John Wiles to reduce installation cost. It will be removed next code cycle. John means well, but he lets his passion for green energy get the best of him and does stupid stuff like this. He lost a lot of credibility over this. Only way it got through was a lobby effort of John and the manufactures to carry the vote. Fortunately this is not Obama Care and will be repelled. Many Jurisdictions amended it out thankfully.

[organic farmer]

Well consider what lightening rods do on roof tops,

On one hand, lightning rods may tend to attract more lightning. On the other hand, lightning rods direct where the lightning happens, protecting other features.

I served on subs for 20 years. Every sub pier has wooden 'power poles' every 40 foot, no power lines [those are strung underneath the piers], instead they have street lights and lightning rods on them. By walking on the pier, you are underneath a string of lightning rods, each rod has it's own ground, and each rod is connected to each other rod via grounding cable.

Today, I am a farmer. I have miles of electric fencing. All of that wire will attract strikes. I do not want any of those strikes to send a power surge toward my house. So I must provide preferred paths for those surges to go to the ground.

You can provide a preferred path for strikes to follow, away from sensitive features, if you want to.