Grounding a Grid-Tied PV Array
I’m self installing a grid connected solar system and have some questions about grounding it. I’m using a 6 gauge continuous grounding wire conductor within each array and to connect 3 arrays together. I’ve read that the grounding conductor must go inside any conduit carrying the other panel conductors connecting the arrays together. However I’ve also read that the steel Emt conduit itself can also be used as the grounding conductor as long each end of any Emt conduit is suitably connected to ground.
What’s the story on that? Also, I’m struggling to conceptualize how to get a continuous bonding path from the water proof junction boxes mounted on the rails to the grounding conductors that the conduit is connected to. I’m sure there is a best practices method to do that but being a diy person I don’t know what that is.
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You're allowed to use EMT as a grounding conductor per code, but I don't recommend it. I specifically write into my electrical specs at work to NOT allow the conduit to act as the ground, I require a seperate ground wire to be pulled inside. The reason for this is that every coupling and connector on the conduit run is a weak spot if the conduit itself is the ground, and all those set screws can corrode if you're using the set screw type fittings. I would, at minimum, require the use of compression type fittings which are more reliable in this regard, but running a seperate ground wire in the conduit is much better.
Usually you can just splice the ground wire with wire nuts like every other conductor. There are some exceptions to this (notably with pool pumps) that require a CONTINOUS ground conductor free of removeable splices. Note that "removeable" part, which is important. Code allows for splices made by "irreversible means" on these runs, which means splices made by exothermic weld or compression (beefy crimp) connectors.
I'm not super familiar with the codes for grounding solar arrays, but if they require a continous ground path, what I would do is use H-tap connectors in the boxes to allow a ground wire to be tapped off for each device as needed. H-taps are a compression splice connector. You need a special tool to install them, but they allow you to tap branch runs off of a main run by "irreversible means" to satsify code. You very rarely see them on residential projects -- they're not even all that common on commercial projects. Electricians I've introduced to them love them. Burndy is a big manufacturer of them. Note that you have to size them for the "run" (main cable) and "tap" (branch cable) conductor gauges. You MUST uses wires within the range of the connector for things to work. You have to also use the correct crimp tool die for the specific H tap you're using. These connectors are not very forgiving in regards to assembly errors.
BTW, if that conduit run is going to be underground at any point I'd use PVC conduit instead of EMT. If the conduit run is all on your home, such as for a rooftop installation, I'd use EMT with compression connectors and a dedicated ground wire inside.
Note that code requires remote disconnects for many solar installations. Don't forget about this requirement.
Bill
Thanks for the information. I think that makes sense, as you said, to not use use the conduit as the sole grounding conductor between the arrays and the main panel. So I’ll take your advice and won’t do that. I will connect the ground wire to the outside of the conduit once for each panel array with a conduit surface ground clamp so that if lightning hits the conduit it has a path to ground from the direct rail ground. The direct rail ground will have the ground wire running “within” the conduit.
I’m using a Solodeck panel to feed the wires including ground wire, through the roof into the attic. It has a ground bus bar with at least three connections so I’ll use 2 for grounding uninterrupted straight runs to each of the arrays and use the third bus bar connection to run it down to the attic. That way I won’t have to crimp any ground wires together. I’m using an Enphase microinverter system that doesn’t require a roof mounted dc disconnect. Just a ground mounted ac disconnect. If the ac disconnect is open circuit it causes all the micro inverters to shut down automatically.
Thank you for the help.
The conduit should be grounded by way of bonding jumpers (ground wires) connected to the metal electrical boxes. If you want to be doubly sure, there are two devices made to ensure the conduit is solidly connected to the metal boxes:
Grounding Locknuts -- these are locknuts with a set screw on one of the tabs. After tightening the locknut, you tighten the setscrew to bite into the metal box to ensure a good ground connection between the two. This is probably what I'd use here
Grounding Bushings -- these are bushings that have a lug on the side to connect a ground wire to. You might not be able to find these in smaller sizes since code only requires them on larger conduit runs with high ampacity circuits in them.
I wouldn't use a ground clamp on the outside of the conduit. Besides looking a little goofy, you also run the risk of galvanic problems. You're better off making sure the ground connections internal to the conduit and boxes are solid. I would use all compression conduit fittings too, which have a circumferencial locking ring and don't rely on just one screw to maintain a connection. Compression type fittings are available at the box stores just like the set screw type, so they're easy to get.
Note that for lightning protection, you need to make sure that the conduit is solidly ground at BOTH ENDS. If you don't do this, the conduit acts as a choke (due to ferromagnetic effects) and will restrict the flow of lightning energy, which means higher voltages will be seen at the far end. Grounding both ends of the conduit cancels out most of this effect.
Note also that lightning grounds need to keep bends to a minimum, and any bends you have to make should be gradual bends. You also want to make sure you have everything bonded at ONE point, which means all the grounds should go to the same spot (telephone, cable TV, power, etc.). One ground rod isn't enough, either. If you have city water with a metallic pipe, make sure that's tied in too. If you're in a high risk area, you might want to consider a ground ring around your house. Ground rings are a lot of work to put in, they typically consist of a buried copper wire of 2 gauge or larger with an 8 foot ground rod cadwelded every 16 feet along the ring, but they are excellent ground systems. I had such a system at my old house and it saved the house at least once ("saved" meaning if the ground ring wasn't there to dissipate the lightning energy, the lightning would have set the house on fire). I have a similar system nearly completely at my current home.
Glad I could help you out.
Bill
I’m using the rain tight compression fittings. Ok, im wondering if I can use the same device that clamps to the rail and has provision for a pass thru conductor inside the box. I’ve checked and it physically fits to the green grounding screw inside the box and of course also to the conductor. Anything wrong with doing that?
Can you provide a link to the "device that clamps to the rail"? I'm not sure what that is, so I can't really comment on it. If you can provide a link I'll check it out for you.
Bill
Here’s a link:
https://www.renvu.com/IRONRIDGE-Grounding-Lug-T-Bolt-Kit-2-pcs
I’d just replace the t-bolt with green grounding screw. Presto…
I don't see a problem using the clips at that link in the way that you describe. If you are going to connect pigtails of wire to those clips, then I would use a crimp-on lug on the wire, and a bolt/nut/lockwasher to make the connection to the climp. I would also use a stainless steel star washer between the lug and the clip to ensure a reliable electrical connection over time (the teeth on the star washer will bite through oxide layers to keep a good electrical connection).
Bill
Do a little more research. Individual panels should be connected together to ground, usually through a connection on the frame. 6 gage is a little overkill for that but a combiner box can be used, similar to how your separate panel arrays are wired, and send the 6 gage directly to ground from there. Some panels have neutrals, some don't, so ground becomes important when wiring, especially to some inverters. So you may still have to run a ground into your setup.
If lightning is a concern or worry, they sell lightning arrestors.
This depends what code cycle you're on. Do you know? Are you installing micr0- inverters? Optimizers? Neither? Rapid-Shutdown? Will this be inspected?
The #6 copper typically only needs to get to the Soladeck. Then you can transition to #10 0r #12 insulated ground in the pipe. But that is dependent on what code cycle you're on.
I see now above you say micro-inverters. In that case you do not even need metal conduit. PVC of even Romex runs are OK.
My understanding is that I want the environmental and electrical protection of conduit “between” arrays. I understand you don’t need it beneath the panels on each individual array and my system won’t have that. Micro inverter systems are a different animal.
conduit between arrays is good, yes.
The grounding protocol will vary depending on your code. If you're on the 2017 or 2020 the only reason to use #6 is if it's "exposed to physical damage." Either way the #6 is fine, moving on. In theses more current code cycles the ground is not a GEC, It's an EGC and is sized accordingly. It also does not have to be one continuous length of wire, splices are OK.
For lightning protection, it is prudent to use larger grounding conductors, ideally #6 solid as a minimum. There are electrical reasons beyond just what is in the code book. The code is a minimum after all, not necassarily "best practice" for a given application.
If lightning protection is a primary concern, that is another reason to use compression splices and not wire nuts. Compression splices are far more reliable. When I am designing grounding networks at work -- and we take grounding very, very seriously in the telecom world -- I spec only compression and exothermic weld connections. I even spec specific types of crimp tools for the compression lugs.
How much lightning protection makes sense depends on the risk level of the area you're in. Somewhere in Florida would be very high risk, somewhere in the far Northern states not so much.
Bill
For a homeowner trying to sort out all the details of a solar electric system I would say the NEC is a great guide. Lightning protection is a whole other beast and may be completely unnecessary(as you say) and just add confusion.