Author Topic: Grid-tie SPD location and grounding with generation meter  (Read 305 times)

daklein

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Grid-tie SPD location and grounding with generation meter
« on: May 24, 2020, 12:04:22 AM »
Hello,     
          I have a question or two about the best way to connect this SPD, and how the GT system ought to be grounded & bonded, especially through the generation meter.  Did I do it right? 

        I just installed a new MNSPD300AC, at the AC combiner box of my roof-top GT microinverter array.  (upper left panel in picture)   Love the little blue lights!

        I already have a surge protector below the main grid service panel (far right in picture), and I had always considered that would protect the solar system.  It may look like overkill to add another.  But I'm going to have this GT system be able to be switched at the main panel, to AC coupled behind a pair of SMA inverters, where they won't be protected by that one, and now I'd have this rooftop lightning collector feeding the fancy SMAs.   So that's the motivation to add another SPD here at the AC combiner box.     

         Please comment if that doesn't make sense.     There will be 3 more MNSPD300ACs in the rest of the system:  one at a ground mount array which will be AC coupled to the SMA, and one at each SMA protecting the AC1/AC2 lines.   Same worry for the ground mount array, feeding the SMAs.     There are additional ground rods;  at the basement main subpanel, at the garage subpanels with the SMA, at a shed on the way to the ground mount, and another at each end of the ground mount array.   Ground & neutral are isolated, except in the main grid service panel.

          The rooftop array has continuous solid #8 from the solar PV disconnect, through all the micros and panels and down to a rod below the array.  I just realized, that ground is (was) not continuous back through the generation meter to the main service ground/neutral bond.  There is a ground wire from the service panel to the other side of the generation meter can, but not through it.    So if I connect the SPD ground wire to the solid #8 ground in the AC combiner or disconnect,  it's relying on the panel conduit and fitting bonds to get back to the real ground at the main panel.   I want to hook the SPD ground to a good solid ground, not the back end of the likely lightning source from the roof?   

          So I ran added a #6 stranded insulated ground from the main panel, through the generation meter, through the disconnect and connected to the #8 solid and the SPD ground in the combiner box.

https://photos.app.goo.gl/8D7K9jZxARWRYSop8

Thanks!    Dale

daklein

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Re: Grid-tie SPD location and grounding with generation meter
« Reply #1 on: May 28, 2020, 04:42:27 PM »
I think I answered or resolved my question, I'm happy with how it's done.   

I looked at the original solar install plans, which show the #8 solid ground continuous from the array, all the way back through the combiner, disconnect and generation meter.   My change effectively makes it that way now.   

Maybe they didn't like running the bare ground through the meter can?   And the ground rod at the roof array (not shown on the plans) might have been a last minute addition to please the inspector or the electrician.  Who knows.

Plans also show larger wire from the combiner box back to the main panel (#6 recommended by the plans, vs #10 used).  It's ok-ish for two microinverter strings, about 20 amps total, but I've always thought larger would be nice for voltage drop.    Now that I've broken the seal on the meter, I'll change it to #6 sometime.

So, watch your installers I guess, or ask the inspector to check the work vs. the plans.   Or actually check the plans and the install yourself (took me 10 years).