Newbie here doing a 20.8kW DYI install (80 sunMAX 260W panels with microinverters)

[foo1bar]

According to the Ironridge installation manual, only a single grounding lug is needed on one of my 12 aluminum rails as the panels themselves create the bond between the rails. Yet the online configurator had me order one lug per rail. Which is right?

All the rails need to be grounded.
The grounding midclamps will connect the modules to the rails - and can be used to connect two rails together (via the module)
So if you have grounding midclamps and 6 pairs of rails you could probably have just 6 lugs.
(I'm assuming 6 pairs of rails, 4 modules per rail, that the rail-to-pipe connection is all that connects each set of 4, and the rail-to-pipe connection doesn't provide a grounding bond. (I suppose it might - I didn't look at it)

[bcroe]

Hmm, here the rule seems to be that all the PV PANEL FRAMES need to be grounded. That being
achieved by one WEEB washer under each panel to the horizontal rail, and the horizontal rails being
WEEBed to a vertical rail, with a grounding lug for a #6 on one rail. Bruce Roe

[pclausen]

This is the page from the Ironridge manual I was referring to that seems to indicate that just a single ground lug is needed:



The "stack" of 5 modules on the left are bonded through the UFO clamps, which in turn transfers to the 2 rails. The stack on the right appears to be bonded through the cross pipes to the left stack. I'll admit that in my case, using black painted pipe, there is likely not a very good bond between the rail u-bolts and the cross pipes. Since I have 12 grounding lugs, I figured I might as well use all 12, one on each rail, and just run a continuous #6 bare copper wire between all 12 rails and then have a single #4 from one of the 2 center rails, down to the rebar sticking out of the cement.

My roof mounted panels use panel connector clamps at all corners, this ensuring a solid bond on both the horizontal, as well as, the vertical plane. So there only a single grounding lug was required per array.

[tyab]

What I think what you are refering to is the WEEB lug. You most likely have one per rail. Put it on the top of each rail (or you can do it at the bottom - does not matter) and you run a #6 bare copper wire across all the lugs horizontally. Take that #6 and run it down one of the vertical pipes and there is your 690.47(D). Remember it has to be continuous since this is a GEC - one run of wire. Either run it into a ground rod or you could run it in a small trench back to the middle and bond it to your ufer. Key is it must be a continuous run and it must terminate into a valid ground electrode and most importantly - that ground electrode must not be used for any other purpose.

[pclausen]

Ok, so I'll take a continuous #6 and run it through all 12 WEEB lugs (what Ironridge refers to as grounding lugs I think), and then tie it into the rebar sticking out of the concrete that is my ufer.

So that I'm clear, the only other ground I need, is to combine the green wires from each of my 2 12 panel strings of microinverters, and run this #10 green back with the other #10 wires to the breaker panel, right?

In other words, I do not need to run another #6 bare copper from the ufer back to the GEC rod at the shop building.

I guess the thing I can't quite wrap my head around is that if I have a lightning strike close by, won't where be a lot of voltage potential between the ufer and the separate GEC at the shop? And the only ground fault path between those potentials will be the #10 green wire going between the ground array and the shop? Thus it could potentially fry all 24 microinverters at the ground array since the ground fault path would be going though the inverter casing to the GND wire and from there back to the shop GEC.

[tyab]

WEEB is the brand name, they are really good for bonding aluminum rails: http://www.we-llc.com/products/weeb-lug

Yes, just combine the green's and run one back, this is your EGC and must be in the same conduit as the other conductors. You do not have a subpanel and thus are not a feeder and thus do not need another GEC. When you combine them - remember it will be in a wet location.

You do not need to run a bare #6 back to the shop - I think if you did (in the ground) it might be a violation since it is not #2 or larger and at least 30" underground. Not sure on that one.

Yes, potentially if you have a near lightning strike that could happen. NFPA 780 addresses that problem but that is a completely different subject. This is what class 1 lightning conductor looks like and this is what you make your ground ring electrode out of for NFPA 780. You use it bond to anything that comes out of ground made of metal. And you have to use listed splices, connectors, bonds and on and on. I'll be doing a large post on this subject within the next two weeks.

[pclausen]

Looking forward to your post. I also checked out all your pics. You dropped some serious coin for wire alone for that 400' run to the house to stay within 2% drop. Would it not have been cheaper to do a single run of say 350 MCM Al?

Anyway, appreciate the confirmation regarding just needing the single EGC in the same conduit back to the shop sub-panel.

So here's what the ground mount looked like yesterday afternoon:



And here's a shot from this afternoon after getting almost 1.5" of rain overnight after 30 days of nothing:



The whole thing didn't collapse and slide down the 150' or so to my lower field.

I had my rubber boots on removing all the 2x4 support, what a mess. Hope it will be dry enough tomorrow to loosen all the bolts and getting everything perfectly centered and then start adding the remaining 9 rails although I really should just be patient and backfill over the footer first, but I'll have to wait at least another 2 days for the soil to dry enough for that. Patience has never been a virtue of mine.

[tyab]

one word - mud. Been fighting that since the weekend - sinking a couple of inches every step - not fun. Mess everywhere.

For that long run I had two choices - parallel 4/0 AL or a single 500MCM AL. Parallel 4/0 gave me 1.5% drop, single 500MCM gave 1.6% just for those runs. 2x4/0 500' spools at Home Depot (online) was less than single 500' spool 500MCM from the local supply place with contractor pricing. And folks I talked to said that 500MCM is a pain to work with and a big pain to pull (I have never worked with wire larger than 2/0 before this project). So I went with the 4/0 from Home Depot. Total voltage drop from the farthest microinverter to the service meter should be just a tad under 1.9% so I'm just under the 2% that Enphase recommends.

I'm sure you read this in the Iron Ridge instructions but does not hurt to repeat - make sure that you follow the torque values, otherwise you can bend those top caps and the rails. The rail galvanized 3/8" U bolts are only 60 inch pounds so be careful.

[pclausen]

Good point about 500MCM being a pain to work with. I had fun stuffing 3 of those into a 4" conduit riser up into my fused disconnect, and splicing it down to 300MCM Cu just before entering the panel. In my case I only had to deal with the 500MCM in conduit for about 6', the rest was all direct burial. I could not imagine pulling 3 of those together thought 400' of conduit. I bet pulling 6 x 4/0 was plenty fun.

Here's my 500MCM spliced to 300MCM Cu. The splices were of course wrapped before being inserted into the 4" conduit.



And here's the final result at the house after being done with the rest of the 300MCM Cu wiring and the "thin" 3/0 Cu into the 200A house sub panels from the Asco xfer switch:



That whole area is going to be enclosed and called my "power room". It will be open on 3 sides since it will house my diesel generator as well. That coil of cable you see, is a run of 24 count fiber between the house and the shop. I'll be switching from my current point-to-point wireless bridge to fiber.



On the voltage drop, I still need to take some final measurements, but I believe I'm right around 1.6% from the microinverters to the disconnect at the house next to the POCO meterbase. My issue is that the power coming in from the POCO is very hot. During the middle of the day (when the load on the grid is minimal), I'm seeing as much as 251V at the meter, which means the inverters are seeing about 255V. Check out this screenshot of me running "suntop" from a ssh session to my solar gateway for the main array (it runs busybox linux).



My concern is that once I get the other 24 panels online, it might pull the voltage over 258V at the inverters, at which point they will start dropping out to stay compliant with UL 1741. I'm digging around in the various config files in the gateway to see if I can up that limit. And this is late November. Imagine what it will be like in June when the panels are producing closer to their 260W rating?

[bcroe]

Agreed, high line voltage can cause shutdowns. I would try pressing your PoCo to get it down to 240V. It took a while, but mine was
even higher for a while till adjusted. Bruce Roe

[pclausen]

I did discuss it with the PoCo already and they say that it is by design that they set the voltage at the sub-stations to 125V between each leg and ground. So that is why I'm seeing 250ish on average. He said that before my street was upgraded from 7.2kV to 14.4kV, it would have been possible to move me to a different tab on my transformer, but not anymore.

Also spoke to Ubiquiti (microinverter vendor) and they told me I might need to invest in an autotransformer. They said that with an autotransformer, I don't need the full power rating, only the voltage you're trying to change. So in my case, with 6 strings on 20A breakers, that would be 120A and a 10V delta, so a 1.2kW transformer. He said I would loose a couple of % hit.

I see going to autotransformer route as a last resort. Anyone else had to go this route, and if so, any comments to share?

[bcroe]

There are standards for line voltage; you might want to investigate and then push back harder.

An autotransformer would work, but its a clumsy solution. For openers it needs to be double ended, because if you try to
make an adjustment on just one line, your inverters might still trip out over the imbalance. If say you reduced 250V to 230V,
the shift of 20V represents 8% and the auto transformer size must be rated proportionally, not trivial at this power level. The
auto might have losses on the order of 1 to 5%, depending on quality. So that looks like losing 1/3% of the peak power, but
since it will be on continuously, day, night, rain, etc the overall losses could run well over 1% of generation. Size it too
big, losses go up; too small, it burns up.

A better way out is reprogram the limits of your inverters, a lot easier if running strings. This in fact is not really so different
from the auto transformer; the inverters now put out the same voltage the auto transformer would have. Bruce Roe

[SunEagle]

There are standards for line voltage; you might want to investigate and then push back harder.

An autotransformer would work, but its a clumsy solution. For openers it needs to be double ended, because if you try to
make an adjustment on just one line, your inverters might still trip out over the imbalance. If say you reduced 250V to 230V,
the shift of 20V represents 8% and the auto transformer size must be rated proportionally, not trivial at this power level. The
auto might have losses on the order of 1 to 5%, depending on quality. So that looks like losing 1/3% of the peak power, but
since it will be on continuously, day, night, rain, etc the overall losses could run well over 1% of generation. Size it too
big, losses go up; too small, it burns up.

A better way out is reprogram the limits of your inverters, a lot easier if running strings. This in fact is not really so different
from the auto transformer; the inverters now put out the same voltage the auto transformer would have. Bruce Roe

It gets hard to be a co-generator. Now you have to meet all of the fluctuations that come along with the grid just to keep your inverters warm and happy.

As for pushing back on the POCO to change their transformer taps. Good luck with that. Their first priority is to keep the grid stable for all of their customers up and down the power line with any co-generator probably being the last ones they help out.

Even Industrial complexes had to fight low and high voltage swings before and after each weekend when the POCO turned on and off their capacitors to keep the HV within spec. It used to cause all types of heartburn for me in some areas of our plant with lights either going dim and motors tripping out to high voltage spikes and it's after affects. We ended up installing voltage regulating equipment on critical control equipment as well as finding a "sweet spot" voltage tap for our distribution transformers. All the POCO did was say we were just one of their many customers and would work with us the best they could which was not very much.

[bcroe]

That is true, but there ARE regulations. Changing the operating point tap is a different issue than regulation/fluctuations. Bruce Roe

[SunEagle]

That is true, but there ARE regulations. Changing the operating point tap is a different issue than regulation/fluctuations. Bruce Roe

Yeah. The POCO has to keep the grid as stable as possible. Of course they can make a claim the problem is not theirs if there are customers on the line causing the issue.

Did I every tell you the story about a waste water treatment plant at the end of the line that was causing a phase angle issue which kept causing a 1 MW solar array at a high school to keep going off line every time they started a couple of their big motors?

We couldn't get their plant to fix the problem but we got the Inverter manufacturer to adjust the anit-island software to be less sensitive and ignore the phase angle issue for 20 more cycles before is shut down. We succeeded but the POCO only raised their hands and said they couldn't do a thing to help. Again they were not very helpful since the school was a 1MW co-generator.

[DanS26]

That is true, but there ARE regulations. Changing the operating point tap is a different issue than regulation/fluctuations. Bruce Roe

Here is what the Indiana Administrative Code says about permissible voltage variation.........

170 IAC 4-1-20 Standard nominal service voltage; permissible voltage variation
Authority: IC 8-1-1-3; IC 8-1-2-4
Affected: IC 8-1-2-33
Sec. 20. Standard Voltage and Permissible Voltage Variation. (A) Each public utility shall adopt a standard nominal service
voltage, or standard nominal service voltages, as may be required by its distribution system for its entire constant voltage service,
or for each of the several districts into which the systems may be divided, and shall file with the commission a statement as to the
standard nominal voltages adopted. The voltage maintained at the customer's main service terminals shall be reasonably constant,
as follows:
(1) For residential service, the voltage shall be within five percent (5%) plus or minus of the standard adopted, and the total
variation of voltage from minimum to maximum shall not exceed six percent (6%) of the average voltage in cities and other
incorporated places having a population in excess of 2,500, nor eight percent (8%) of the average voltage in all other places.
(2) A greater variation of voltage than specified above may be allowed when service is supplied directly from a transmission
line, or in a limited or extended area where customers are widely scattered or the loads served do not justify close voltage
regulation. In such cases the best voltage regulation should be provided that is practicable under the circumstances.
(B) Variations in voltage in excess of those specified, caused by (1) the operation of power apparatus on the customer's
premises which necessarily requires large starting current, (2) the action of the elements, and (3) the infrequent and unavoidable
fluctuations of short duration due to station operation, shall not be considered a violation of this rule. (Indiana Utility Regulatory
Commission; No. 33629: Standards of Service For Electrical Utilities Rule 18; filed Mar 10, 1976, 9:10 am: Rules and Regs. 1977,
p. 354; readopted filed Jul 11, 2001, 4:30 p.m.: 24 IR 4233; readopted filed Apr 24, 2007, 8:21 a.m.: 20070509-IR-
170070147RFA; readopted filed Aug 2, 2013, 2:16 p.m.: 20130828-IR-170130227RFA