Grounding ground mount array (and other questions)

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Vonze

Member
Location
Central New York
Spent a lot of time reading other threads and watching Mike's videos, all helpful, but still have some uncertainty (newbie at PV). Have (2) small arrays, 10 ft. apart with (5) 280W modules each, possibly add a 3rd in future, enphase M250 microinverters with integrated ground. 1) Sizing conductor: 15 x 1.0A (AC output rating at 240 V) x 1.25 = 18.8A @ 75C @ 100 ft. => 10 AWG. (1.9% Vdrop or "Vrise" if you read enphase literature) for L1, L2, N. Will drop to 12 AWG to split to each of the (2 or future 3) arrays. If there's something worng so far, I'd appreciate a heads up, like could N be smaller all the way? 2) Plan on (1) combined disco at arrays (I know it's optional) and at house near utility meter (no line of sight), then 20-A 2-pole backfeed breaker. Don't think discos need to be fused? 3) These microinverters need no DC GEC, have only EGC in wiring harness. Intend to bring that back to AC load center gound lug. Will use grounding clamps from modules to rails and grounding lugs on rails (Ironridge says only need to pick up 1 of the 2 rails, but may just do both). Both array and inverter ECG's bond together per: http://enphase.com/global/files/Enp...d-Ungrounded-Arrays_Whitepaper_English_NA.pdf, page 3. Everything I've read indicates the array EGC should be no. 6 bare. My real Q is the size of the combined EGC back to the main panel? Can't seem to get a handle on that. If 10 AWG (or smaller?), is it okay to bond the no. 6 array ECG to it? BTW, I already ran a 1" PVC buried conduit, hope I'm not in trouble there. 4) Then there are my metal supports (not Ironridge pipe system, but my own 2 position tilt design) anchored to concrete piers. What should I do for those with repect to grounding? Nothing required? Supports are comprised of many pieces: uprights with a pair of yokes, tilt arms, bracing and brackets and bolts. It would be very hard to bond ground straps to every single piece. Thank-you and God bless.
 

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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
On a first read I see nothing wrong with your plan. Nothing I would do differently, in fact.

Don't think discos need to be fused?

Nope.

My real Q is the size of the combined EGC back to the main panel?

It needs to be #10 since you are upsizing your other conductors for voltage drop.

If 10 AWG (or smaller?), is it okay to bond the no. 6 array ECG to it?

Yes.

Then there are my metal supports (not Ironridge pipe system, but my own 2 position tilt design) anchored to concrete piers. What should I do for those with repect to grounding? Nothing required? Supports are comprised of many pieces: uprights with a pair of yokes, tilt arms, bracing and brackets and bolts. It would be very hard to bond ground straps to every single piece.

Here is what the code says: you must bond any parts that are "likely to become energized". Your inspector might ask you to bond the supports below the rails, although in my experience that is usually not asked for. In my opinion if you have an all stainless and aluminum rack that is all tightly bolted together, and you've bonded the rails, then you shouldn't need to bond small parts or supports since they are pretty much guaranteed a good metal-to-metal connection to the rail. But there's a slight wrinkle in your case, which is that your 2 position rack presumably features either a rotating joint or some removable/adjustable parts that may not always provide a durable metal-to-metal connection that would carry electrical current if one or the other side were energized.

An inspector may also ask you to put a ground rod at each array, because of 690.47(D). This is an unnecessary and in my opinion stupid requirement (especially since your numerous supports in concrete piers probably provide a better ground connection that a rod). But an inspector may require it.
 

Zee

Senior Member
Location
CA
On a first read I see nothing wrong with your plan. Nothing I would do differently, in fact.



Nope.



It needs to be #10 since you are upsizing your other conductors for voltage drop.



Yes.



Here is what the code says: you must bond any parts that are "likely to become energized". Your inspector might ask you to bond the supports below the rails, although in my experience that is usually not asked for. In my opinion if you have an all stainless and aluminum rack that is all tightly bolted together, and you've bonded the rails, then you shouldn't need to bond small parts or supports since they are pretty much guaranteed a good metal-to-metal connection to the rail. But there's a slight wrinkle in your case, which is that your 2 position rack presumably features either a rotating joint or some removable/adjustable parts that may not always provide a durable metal-to-metal connection that would carry electrical current if one or the other side were energized.

An inspector may also ask you to put a ground rod at each array, because of 690.47(D). This is an unnecessary and in my opinion stupid requirement (especially since your numerous supports in concrete piers probably provide a better ground connection that a rod). But an inspector may require it.

What Jaggedben said is excellent.

I would just add: aluminum rail and aluminum module frames when bolted to each other - or other metal - DO NOT create a good metal to metal connection (grounding path). The aluminum is either
1. anodized in the factory (often clear and invisible) or
2. just by being in air, aluminum "self -anodizes" and creates a tough insulating layer.

I doubted this idea myself.......and so put a continuity tester on a rack: yup, module to rail even when bolted together: no continuity.

However, galv. steel and stainless steel should all be good metal to metal connections.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
... I doubted this idea myself.......and so put a continuity tester on a rack: yup, module to rail even when bolted together: no continuity.
...

Well, if you're putting both of your probes against an anodized surface then you often won't get much continuity. ;) I have doubted that modules were bonded with WEEBs and such, until I found that the inside surface of mounting holes is often not anodized and I get continuity to a copper ground when testing there.
 

Vonze

Member
Location
Central New York
Thank You

Thank You

Big thanks to "jaggedben" and "Zee" for reassuring feedback. I finished installation using grounding mid-clamps on module frames to rail, then WEEB lug on one of the two rails to bare conductor into j-box to EGC. I did not bond any grounding to the steel supports and it sailed through inspection.
 
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