Sub-Arrays, Branch Circuits, Combiners, and Home Run

[bryankloos]

Hey Guys,

I need a little help here, trying to see if I'm doing things as the experts would...

I am planning 2 arrays, 1 on the East roof the other on the West Roof.
West roof has 3 strings (14, 14, 13) panels, and the West has 2 strings (14, 14) panels, all with S280 micros.

I plan to run each trunk cables to a soladeck (1 for the east and another for the west arrays) so that no conduit is showing on the roof.

Here's where I get a little confused.

My plan from here is to bring the feeds from each array (3 from West, 2 from East) through 3/4emt to another JB where I will transition to 1.5"emt for the home run to my solar ac panel and then to disco and to line side tap. OK, this is fairly straightforward, or so I think.

The engineering report shown #10 THWN-2 from the soladeck to the first JB, and then #6 from the second JB (where I transition to 1.5"EMT) to the solac ac panel/combiner in the basement.

If this is in fact correct, which I suspect it may be, I'll have 10 energized lines, a N and a G in the conduit for home run pluc my GEC connection to the array... This is a LOT of #6 wire.

Is there a better way to do this to cut down on the amont of #6?

Also, in this scenario, how would I transition from #10 to #6 in the JB that combines the lines to a single conduit?

I have the line diagram, but I'm not quite sure how to post it, being a PDF...

Any Thoughts?

Thanks,

Bryan

[bryankloos]

The more I think about it, the more logical it seems to put the dedicated solar AC panel in the attic, and just run one line (L1,L2,N,G and GEC) down the 1.5" to the disco and then line side connection.... Thoughts?

[SunEagle]

What is allowed per the electrical and safety codes in your location? If you have submitted a set of electrical drawings then any changes might have to be reviewed and approved by you AHJ.

IMO if you have the money to install 69 panels & micros (~20kw) the cost to safely run the #6 wire (per the design) should be a slam dunk. Now is not the time to cheap out and change the design to save a few bucks.

[bryankloos]

I don't disagree... I'm not looking to skimp out on anything, hence why I'm asking here.
I just though it may be easier to run fewer larger wires through 50' of conduit versus many smaller wires...
I have not submitted yet, and want to get everything in order before I do to avoid any changes.
I'm getting close, just trying to work trough some of the last details before I submit.

[sensij]

Yes, put the combiner in the attic. No reason I can see to do the combining so far away.

[SunEagle]

I don't disagree... I'm not looking to skimp out on anything, hence why I'm asking here.
I just though it may be easier to run fewer larger wires through 50' of conduit versus many smaller wires...
I have not submitted yet, and want to get everything in order before I do to avoid any changes.
I'm getting close, just trying to work trough some of the last details before I submit.

I understand. Just make sure you derate the amp rating of all of the cables carrying power in the same conduit. Once you get above 4 the NEC requires you to use a multiplier. For 4 to 6 conductors use 80%, for 7 to9 use 70%, etc. This is required due to the heat generated by more than 3 current carrying cables.

Also each conduit size is allowed a specific number of wires of the same AWG to be run in it. You need to check what a 1.5" emt can fit. By code 16 #6 THWN are allowed.

[Eleceng1979]

Originally posted by sensij View Post
I would suggest ignoring what eleceng1979 wrote in the post above this one... lots of misinformation in there.

[bryankloos]

Thanks for a very complete response, Eleceng1979. I appreciate all that you are stating and the advice given.

The attic is a walk up, with floor and great ease of access. I'm going to ask my AHJ his thoughts, but I suspect he will be okay.

When I wrote 6AWG, I was referring to the ground... The wire as specified from my engineer is 3AWG from the 125A sub/combiner to the disco and line side connection.

My plan was to run the wires back indoors after the AC disco into my MSP, where I would tap into the line side with Polaris connectors.

I know the POCO here will allow line side tap, and I will look into the feasibility of my 200A service with a 100A line tap. I appreciate you bringing this to my attention.

While a partial DIY, I am pulling all permits, filing all applications, and have professional engineering plans for the system and the roof structure.

I'd like to think I am covering my bases, but yes, I am not a professional. I run a small in vitro fertilization lab during my daytime hours and tinker in the evening hours when not spending time with my family, who I have not intention of hurting with a fire or any shock hazard. That's why I'm here asking the pros, and again, I appreciate everyone's help.

[Eleceng1979]

Originally posted by sensij View Post
I would suggest ignoring what eleceng1979 wrote in the post above this one... lots of misinformation in there.