Panels mounted on steel structure, is grounding required?

[mike95066]

I had posted this in the beginners section already, but did not get a response. Maybe this forum is better.

I moved my panels from roof-top to a concrete platform, with lots of rebar in it. I'm estimating 10,000 ft of 5/8" rebar that is all connected. The rack structure is 80% steel and 20% aluminum and is connected to that rebar.

Do I need to ground all the panels, the same way they were grounded on the roof, and do I need to run the ground back to the inverter? Aren't they already grounded? 3rd option, drive a new rod at the new location, and ground to that rod.

Here is the link to my other post, maybe I was too wordy.

 

[kernel]

Depends on how they are connected to the rebar. There is likely no good way to bond to it or ensure that the connection you have will keep continuity.

Ground as you did on the roof and connect to the egc system. You can bore the concrete at the foot of the array mount and add a supplemental ground rod if you like.

 

[mike95066]

All the rebar is tied together with wire. The posts are welded to the rebar. The entire structure above the concrete is welded together except the joint between steel and aluminum.

When working with a welder, we've connected one clamp to a stub of rebar that we left protruding from the retaining wall, and when the welding electrode touches the steel structure as far as 100' away, there's a good connection.

So for a 250A arc welder's output (35V @ 250A?), there's definitely a good enough connection.

You're right though.. the rebar will oxidize, even if there's a minimum of 3" concrete, moisture will get to it.

Thanks for your response.

 

[kernel]

All the rebar is tied together with wire. The posts are welded to the rebar. The entire structure above the concrete is welded together except the joint between steel and aluminum.

When working with a welder, we've connected one clamp to a stub of rebar that we left protruding from the retaining wall, and when the welding electrode touches the steel structure as far as 100' away, there's a good connection.

So for a 250A arc welder's output (35V @ 250A?), there's definitely a good enough connection.

You're right though.. the rebar will oxidize, even if there's a minimum of 3" concrete, moisture will get to it.

Thanks for your response.

Cad welds may be required to defeat corrosion long term. Its what we use when building similar grounding networks for cell tower facilities. I can still taste cadmium in lightning storms!!

 

[mike95066]

Unfortunately, when we built the retaining wall and platform, it was meant for a couple of water tanks only, we did not have grounding of anything in mind. We were more concerned about the water's weight (10k or 15k Gallons). The concrete was poured nearly a year ago. To move the solar panels there was an afterthought, as the roof needs replacement.

Thanks for pointing me to "cad welding". I had to look it up, found a good video.

I'm going to buy some 10 gauge copper to ground it.

 

[kernel]

Unfortunately, when we built the retaining wall and platform, it was meant for a couple of water tanks only, we did not have grounding of anything in mind. We were more concerned about the water's weight (10k or 15k Gallons). The concrete was poured nearly a year ago. To move the solar panels there was an afterthought, as the roof needs replacement.

Thanks for pointing me to "cad welding". I had to look it up, found a good video.

I'm going to buy some 10 gauge copper to ground it.

Love to help the community.

 

[kernel]

I wouldnt fuss too much. You cannot protect 100% from lightning, you just cant.

If you are welded to the rebar and connect the array to your ground conductor system at the building and include a surge arrestor (midnite spd only one worth using, silicon dioxide is a joke amd a mess!) Between a.d before entering into your power room or building you amd your electronics will be fine.

Technically your pv wiring cannot come into contact with your rebar, so...... its like metal roofing. We do not nor could we for all practicallity bond every sheet. So the wiring is installed amd designed to not be able or likely to come into contact with it.

I have seen photos of lightning blowing out huge chunks of concrete on its way and side step the ground system nearby entirely. It is why i bond battery negative to ground (egc, but dont do it, im not suggesting you do)..... dc negative electromagnetic lightning protection ala ham radio and telecom technology.

 

[Bill Taylor]

The NEC specifically addresses this. It is referred to as a concrete-encased electrode. In the trade it's called an "Ufer", named after it's inventor. The International Association of Electrical Inspectors considers this to be the best and most durable ground available. Search "concrete-encased electrode IAEI". In your case, it may even be a code requirement to bond that ground to your existing service entrance ground. If your mounting rack system was designed and listed to act as a grounding conductor, you are good to go as long as you used #4 copper and the proper ground clamps (they make ones that are listed for use with rebar).


PS- My answer to your question was given from an electrical contractor / building inspector / code compliant standpoint. I totally get the off grid "under the radar" route some people choose to follow. Not sure which side of that you land on, just thought I'd throw my two cents in.