GEC for PV system in large commercial bldg.

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Jeff Greef

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I'm an inspector. Contractor installed small PV system on the roof of a large commercial office building built in 1972. Inverter is on the top floor beneath the panels, next to a subpanel with an EGC. They crimped the GEC to the EGC, which made me cringe. The crimp that cringes. I like it.

Electrician on a TI in the building laughed when I said we need to find the GEC to irreversibly bond to. He claims in buildings this old there were no electrodes required (California). The building itself is fed off a service in another building on site, the main D panel in building with the PV doesn't have a ground bus bar and nothing that is obviously a GEC. It's on the 2nd floor, fed directly from the other building.

Contractor wants to bond to building steel, but we have no way to verify whether this building steel meets the requirements for building steel to qualify as an electrode. I could make him bond to the water pipe in the basement, but that's a lot of work to put him through. Transformers can be bonded to the water pipe anywhere in the building for an electrode connection, so maybe we can allow this as 'alternate methods and materials'. Sprinkler pipe is close by too.

I think we should have him bond to sprinklers, building steel, and water pipe at a main trunk line, not a branch line, and leave it at that.

Thoughts?
 
None of this is really specific to the solar. I think basically it comes down to what is an acceptable Grounding Electrode System for you. He must install that, and then bond the solar GEC to it.

Where I live they have a strict interpretation of Art 250 and require at a minimum bonding a GEC to the water pipe less than 5 ft from where it enters the building, plus two ground rods, and usually the gas as well.


Jeff Greef said:
next to a subpanel with an EGC. They crimped the GEC to the EGC, which made me cringe. ... the main D panel in building with the PV doesn't have a ground bus bar
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So where does the EGC for the subpanel terminate? Just curious, it doesn't necessarily affect the question.
 
The main panel in this building is not a large switchgear, I think the EGCs just go directly to the main panel in the other building, with no apparent connection to earth in the second building at all, which is scary. Electrician said this is common for buildings in this area circa 1972. There's a transformer in the room, we saw no wire outside of the conduits headed toward steel or water, and nothing like a GEC run up through the floors to bond to.
 
I'm assuming that the first building does have a grounding electrode system. The building steel of the second building just needs to be tied into the existing grounding electrode system in the first building. Looks like you might have found a nice collection of code issues that need to be fixed. I always tell people that once you start messing around with the existing electrical system you own whatever problems you find and you need to fix them to make sure the installation is safe.
 
I've been thinking about this one and I think I have an alternate way to comply. If the existing EGC is sized so that it would also meet the DC GEC requirements and is unbroken on its run back to the main panel then it could be converted to act as a combination EGC/DC GEC as called out in 690.47(C)(3). The connection to the existing EGC can be made by crimping to it in the panel and the conduit would need to be grounded.
 
At one time or another I have heard people say that in a situation like this there needs to a be a grounding electrode at the separate building. Was that an old code requirement that has been removed? I can't seem to find that requirement in the 2011 code.
 
My local electrician/inspector friend is of the belief also that they need to get to a building electrode one way or another. Marvin- your idea of using the feeder EGC to get to the other building GEC sounds unique indeed, and seems to meet the intent, though I guess we should open up the main service in the other building and see where the EGC goes, since it should connect to the GEC with no splices by my understanding.

I'll let my Building Official make the call....

Thanks guys

Jeff G.
 
Jeff Greef said:
see where the EGC goes, since it should connect to the GEC with no splices by my understanding.
Click to expand...

(Or with irreversible splicing, I'm sure you mean...)

Actually, the 2011 and 2008 codes allow you to land a combined solar GEC/EGC in a grounding busbar. See 609.47(C)(3)

With that said, every jurisdiction I work in requires an irreversible connection to the premises GEC.
 
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