2014 NEC 690.47(D)

[wallepog]

I'm caught between installing that extra grounding electrode and not. Some background: I'm an electrical engineer designing commercial rooftop mounted PV systems. I've watched Mike Holt's video about it and am reluctant to add an extra electrode into the design.

This is for an ungrounded PV system. The racking is all grounded back to the main switchgear. So in short, the racking would be grounded twice; once going back to the switchgear and the other going to the earth.

For Exception No. 1, I've read that the use of "integral with the array" refers to systems where the array and inverter(s) are installed on the same building. Our string-level inverters are indeed located within the array.

It seems this is more of an opinion of what the "load" means. Any opinions or thoughts? Anyone run into this issue with inspectors or other AHJs?

Let me know if additional information about the system is needed.

Thank you!

 

[Smart $]

I am not of the same impression. I take "load served by the array is integral with the array" to mean none of the PV system power leaves the array... IOW, all equipment powered by the array is also part of the array (or mounted thereto).

With your project being a rooftop array, isn't its support structure bonded through mechanical attachment to the structural [metal] frame of the building? If the structural steel qualifies as a grounding electrode, then no auxiliary electrode is required per last sentence of 690.47(D).

 

[wallepog]

Thanks for the response!

The rooftop array racking is connected to a ground bar which connects back to the ground bar in the main switchgear.

I recently discovered we may use the metal frame of the building as the additional electrode, but I'm curious about the word, "directly". "The electrodes shall be connected directly to the array frame(s) or structure."

The racking is indeed connected to the metal frame of the building, however not directly. It runs back to the ground bar in the main switchgear where it then hits the metal frame.

In light of this discovery, is a grounding electrode conductor needed to connect the racking directly to the metal frame?

 

[Smart $]

...

In light of this discovery, is a grounding electrode conductor needed to connect the racking directly to the metal frame?

Not if the racking connects directly to the metal frame of the structure, which also qualifies as a grounding electrode. By connects directly, I mean bolted to or otherwise secured using electrically conductive means under 250.8. I think a bonding jumper would also qualify, but JMO.