Grounding, grounding

[beechigby]

I am adding a 2 strings and a 2nd SMA SB3000US inverter to an existing system, in essence a double. the 2nd PV array is next to the first, and the 2nd inverter is next to the first.
the 2 new PV source circuits headed to the Inverter mounted SMA DC Disco (with string fuses and ground fault protection built in) are in a new and separate PVC conduit; the run from array to Disco/inverter is less than 14' on the roof, and 5 ' inside concrete utility room.
the EGC/GEC on the 1st array is #6 and run from the rack + PV panels in the conduit with the PV source circuits down to the 1st inverter Disco and connected to the PE terminal, then out to the utilty service ground rod.
the 2nd array has a #6 wire that runs @5" and connects to the 1st array. there is no green wire in the 2nd conduit with the new PV source circuits. AT the 2nd inverter, I have a #6 going to the final PE terminal in the 1st inverter. Is this correct?
Is it ok to not have a green wire in the 2nd array source circuit conduit (it is a short run)?
would it be better to run the 2nd arrays rack + PV EGC/GEC (could it be #8?) tie to the first array, catch all grd lugs on rails of the 2nd array, then enter the new surce circuit conduit and down to SMA DC disco, and on the existing grd rod?

 

[jaggedben]

It would be better for the 2nd array to have an EGC run with its own source circuits in their own conduit. The EGC is necessary for the ground fault detection, and it's not a good practice for that EGC to run through another inverter. At the very least, if you ever removed the first inverter (say, to replace it), you'd need to put in a bonding jumper while it was gone. Best to avoid that situation and run the EGC directly to the new inverter.

The EGC doesn't need to be a #6 in the conduit. It can be whatever size your source circuit conductors are. Some inspectors want to see a #6 on the array, some don't. (If you want a larger wire as a GEC because of lightning ... well, that may be fine but the code doesn't require it.)

 

[beechigby]

would u recommend that the 2nd array not be tied to the first array on the roof?
sounds like I could run a #10 or (my ahj might like a #8) from 4 rails grd lugs in conduit with 2 source circuits, down to on of the PE terminals in SMA Disco, then a #6 GEC from 2nd PE terminal to my existing grd rod. Right? and thanks very much for your quick and clear reply? quick one next. would you install a MidNite surge suppression on the DC source ciruit in the SMA Disco. that might be hard to do in Disco as there is no combined terminal. u would have to run the SS leads into the spare + and -ve in the inverter body.
what do you think?

 

[jaggedben]

would u recommend that the 2nd array not be tied to the first array on the roof?

From a ground fault protection point of view, it may be better to not have them connected, especially if the source circuits are in separate conduits. The overall length (and thus resistance) of the EGC should be similar to that of the grounded conductor, or else the ground fault fuse may become less sensitive to a fault. With that said, tying the arrays together is not necessarily a critical issue. As a counter example, I have run source circuits for different inverters in the same conduit, with a single EGC that was tapped in a box to go to each inverter. In that case, though, removing an inverter would not have interrupted grounding for the other inverter, and the EGC followed the source circuit conductors in all the conduits.

From a lightning point of view, whether it's good to tie the arrays together ... it's hard to say.

sounds like I could run a #10 or (my ahj might like a #8) from 4 rails grd lugs in conduit with 2 source circuits, down to on of the PE terminals in SMA Disco, then a #6 GEC from 2nd PE terminal to my existing grd rod. Right?

That will typically be acceptable here in California.

and thanks very much for your quick and clear reply? quick one next. would you install a MidNite surge suppression on the DC source ciruit in the SMA Disco. that might be hard to do in Disco as there is no combined terminal. u would have to run the SS leads into the spare + and -ve in the inverter body.
what do you think?

The SMA disco does have a combined terminal, but it is only meant to be used with a separate combiner. I don't know much about the Midnite product, but from looking it up it seems you'd either need to use a separate combiner, or purchase one suppressor for each source circuit.