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

[pclausen]

Thus your #10 is able to able to support 12.42 amps inside of PVC assuming your historical high is 100 so you use the #10 and do not have to increase the conduit size due to having to use larger wire. You don't have to increase conduit size due to temperature - only due to number of wires and the size of the wire.

Now we switch to 690 to make sure that #10 wire is ok for microinverter string. Here you need to know the number of microinverters per string and what is the current limit of the microinverters. I'm going to use the Enphase M250's I am using since the math for them is really easy. Each M250 is current limited to 1 amp output.
Lets say we have 8 microinverters per string, so the output is 8 amps.
We must apply a 125% factor via 690.8(B)(1)
8 amps x 1.25 = 10 amps.

In my case I will have 14 panels per string. My microiverters are rated for 1.05A output. So that is 14 x 1.05A = 14.7 Amps. Then we have the 125%, so that is 14.7 x 1.25 = 18.375 Amps. So I think that means I do have to increase the PVC to 1 1/4"? My End Run connectors won't accept anything larger than #10 wire, so bumping the conduit up one size seems like the only option. Pretty much 100% of my conduit will be under the panels and thus in the shade, but I'm sure the AHJ won't see it that way.

[pclausen]

After seeing Jack's Solar Ground Mount Journal, I'd thought I'd pass along to future ground mount DIY'ers a better, faster, cheaper and safer way to build a ground mount. Especially if you are building with 3" HEAVY schedule 40 galvanized pipe.

It is not necessary to build those 2x4 framing support members and having a crew of people around to accomplish the ground mount. The pic below shows a method using just one person to properly set and align a ground mount. Here's the method:

Auger the hole to IronRidge specifications....no need for Sonotubes. Square the rectangle by measuring the diagonals BEFORE drilling the holes.
Use crushed stone to set the height of the pipe by adding or subtracting stone in the hole....use a laser level....any good rental outfit will have one
Set the pipes in a row with mason string.
Using a standard carpenter level make the posts perfectly horizontal and vertical with the small adjustment wood pieces as shown in the pic.
Now with everything leveled and square....just pour the concrete.......one person and job is done.

I picked up 7 3" Sch 40 pipe yesterday in the standard 21' length. 4 of them are threaded with couplings on one end. These will be my horizontal pipes (2 of them cut down to give me my ~32' total length). The 2 cut ends and the 3 non-threaded ones, will be used for my 6 vertical posts. This is regular black pipe (much less expensive that galvanized). I'll be sanding them down and painting them. Given the East West slope, I will have to use Sonotubes at one or two of the South West holes, but hopefully that will be it. I will be using your trick of drilling cross holes through the lower part of the vertical posts and inserting a piece of rebar, vs. suspending the entire post midair before pouring.

I plan to have my final inspection done and have the AHJ and POCO rep out to sign off on everything once the 56 roof panels are done so that I can get those online. I can then take my time with the ground mount and just cut those in when they are done.

[tyab]

Look carefully at the electrical conduit. I missed this last night but I read 352.12(D) again carefully (this is under Uses Not Permitted)

"Where subject to ambient temperatures in excess of 50C (122F) unless listed otherwise."

I missed the last thee words - unless listed otherwise. So I went and looked at a 1-1/4" standard 90 sweep that I had in a box and it is clearly listed on the side for 90C. So look at whatever PVC you are using and see what is stamped on the side (this was a CANTEX sweep - others may be different and straight runs may be different). And we redo the calculations based on whatever is the lowest listed PVC.

But you have a bigger problem. I thought that you already figured that #10 was ok and was just looking at this from the point of view of make sure the pipe could handle the heat ( I thougth your strings were small). But you need to start from scratch and make sure that #10 even works. (it does not). Lets assume that all of your raceway supports 90C and you are using 90C THWN-2 wet wire.

We need to start from scratch here following 690.8 to compute your wire size needed.

1.05 amps * 14 = 14.7 amps
14.7 amps * 1.25 = 18.375 amps.

This string must be protected by an OCPD (over current protection device aka circuit breaker), so you have to round up to the next available trade size. 20 amps.

Your wire must support 20 amps in the intended configuration since that is the OCPD and conductors must be sized according to the OCPD protecting them.

Lets assume that 100F is correct for your high so we use the numbers from previously.

20 amps * 1.7 * 1.71 = 58.14 amps.

Looking at the 90C column you need wire that can support 58.14 amps, that would be #6. (#8 is 55 amps, too small, #6 supports 75 amps)

I use this calculator for raceway fills:

http://www.electrician2.com/calculators/rf_calculator.html

Now trying to fit in 11 conductors of #6 - you need 1-1/4" conduit. You don't need #6 EGC - we would have to go through the cals to compute what EGC works - I can help you with that this evening but gotta run right now.

Sorry to be the bearer of bad news - normally this is all computed as part of your permit application prior to buying it.

Connecting stuff to #6 is not easy - I'm using Polaris Grey's to do it but they are expensive. I'm using #6 due to voltage drop issues due to length but my my max current in a string is 8 amps.

[sunnyguy]

20 amps * 1.7 * 1.71 = 58.14 amps.

I think it should be 20 / 0.71 / 0.7 = 40.24A

[pclausen]

Well, looks like I'll be doing EMT after all. No way I'm going to run #6 (or even #8) from the strings to the panel. The End Run connectors have a 1/2 NPT on them, and their screw terminals won't accept anything larger than #10. I guess the moral of the story is to not use PVC for anything exposed to sunlight.

[tyab]

Sunnyguy is correct - I was in a hurry. You divide. so you have 40.24. Thanks for checking - and a lesson on being in a hurry and not taking to time to get it right. Thus you need #8 wire since 40.24 is greater than 40 amps for #10.

Technically you need #8 wire - no matter the conduit. But 40.24 is so close to 40 - maybe the inspector won't notice and you just run #10. If you had #10 in the docs submitted for the permit and it was approved - odds are you will be fine on the inspection - they usually are just checking to see that the implementation matches the line diagram. Be aware however with #10 when your system is at max output - lets say a really clear day at noon to 1pm - and it is a hot day - the wires will get hot - close to 90C if everything lines up perfectly. In the real world - not likely and you will be fine.

If you went to #8 then you would have to splice to those terminals - least expensive and easy would be a wet rated wire nut and have a #10 and a #8 in it. Ideal 30-1263J can do that that. But not sure if you have room in there for 3 of those.

You only technically need the #8 once you combine all those 1/2" runs into your 1" run - so you could run #10 to each terminal and then switch to #8 when you combine into the larger conduit. Make sure to check out 314.16 for the size needed for that junction box no matter what wire you use or switch to - table 314.16(B) makes it easy for small wires.

[pclausen]

Thanks once again for the valuable feedback. Yes, the inspector approved the plans using #10. I might pick up some #8 since all the #10 I have on hand (from about 10 years ago) is only THWN as opposed to THWN-2. So he would probably fail me on that alone.

Made good progress today.



Got the 1st array done just after sunset.



In case you're wondering what that yellow cable it, it was me testing each string to make sure everything was working before continuing with the next string. Fortunately all 4 strings worked fine.



Also picked up my 3" pipe for the ground mount.

[pclausen]

I picked up some 1/2" flexible metal watertight conduit along with some water tight fittings. It screw on fine to the End Run connectors as seen here:



However, it looks to be rated at only 60 degrees wet. Is this going to be ok?



I got all but the last 2 panels completed today.





Here are a couple of close ups of the panel back side and microinveters. I do like how this is all from a single vendor and everything just snaps together.





Closeup of one of the mounts:

[Mike90250]

When you get that cable up to 60C, you are going to have a lot more problems . Dont worry about that, when it's wet. its going to be cold

[tyab]

So the 1/2" flex is 60C rated when wet - all outdoor conduit is wet. Lets do the math for each string.

14x1.05x1.25 = 18.375. Round up to 20 to match the OCPD.

2 conductors do not need adjustment (ignore ground and neutral with microinverters) - so temperature only.
Assume that 100F from before is valid and on roof so: 20 amps x 0.71 = 28.17 amps

#10 copper at 60C allows up to 30 amps so you are good!

You are making some great progress. I really like the wire layout of that system. For that flex just have enough supports so in the middle of the summer it does not droop down onto that metal roof.

Ya if the wire was not THWN or THWN-2 they would catch that. If there is a lowes or home depot not too far from you they sell #10 southwire simpull - great stuff.

[pclausen]

Appreciate the feedback as always!

So on the wire, this is what I have on hand:



The green is THWN-2 rated, so I'm good there. The white and red are both THWN rated, so I'm good to use those that as well?

Red wire label:



White wire label:



I'm out of black #10, so I'll look for that Southwire simpull. I got both a Lowes and a Home Depot less than 20 minutes away.

I got a pipe boot from pipeboot express, so about the only other thing outstanding is to get a junction box in which to terminate the 4 1/2" flex conduits and then have a single exit for 1" or 1 1/4" EMT, that will then go down through the pipeboot, and onto the breaker panel. The easiest would be to just pick up one of those grey PVC Carlton 6x6x4 boxes from Lowes and drill the 5 holes I need into it?

[tyab]

THWN means that it has its own wet rating (typically 60C) and it is lower than dry rating . THWN-2 means that both wet and dry have same temperature rating (typically 90C). From the sticker THWN will be ok since we are using 60C for the conduit.

#10 black 100 ft spool is about $25 at both Lowes and HD.

It is ok to mix THWN and THWN-2 for your circuit - the key is just to not exceed your design temperature which is 60C for you which #10 won't. If you are bored, 310.10 talks about some of this stuff - I had to review 310.10(H) for my parallel run and this is where you can't mix insulation types.

[pclausen]

Thanks. While I was at Lowes picking up my 1-1/4" EMT, I went ahead and picked up a couple of extra 100' spools of each color, just in case I run out. If I don't, I'll just return it unopened.

Got the 1-1/4" EMT all installed. It is right at 40' total distance from the hole in the roof, to the breaker panel.

Here are some pic. This first one shows the entire run.



Here's where it drops into the panel.



And the turn up onto the ceiling.



And where it penetrates to the roof. Had to use a pallet as a working platform.



And finally the view from above. This pic was taken before the conduit was installed inside. It is now perfectly parallel with the roof-line. As you can see, everything will be hidden below a solar panel, so things should stay nice and dry.

[tyab]

I seem to recall a code section that only allows 5 ft of energized conductors inside of a structure from a PV system before a disconnect but for the life of me I can't find it (it might have been DC only - or it may have been 2011). There is a 5ft requirement as part of rapid shutdown but microinverters by design easily meet rapid shutdown so that is not it. I'll look at 690 and 705 later tonight when I have more time.

Bending 1-1/4" EMT is some serious bend power - you did an amazing job. I'm really jealous of your shop.

[pclausen]

Hopefully the 5ft rule is related to DC only.

I cheated on the 1-1/4" EMT bending and used 3 90s and a 45 at the ceiling ridge. So all I had to do was make 4 straight cuts.