Need advice on drawings

[foo1bar]

Enphase M250 has a limit of 16 micro inverters per string. 16*1.25=20
I have 2 strings of 9 inverters. 9*1.25=11.25 but my system will come shipped with 20 A breaker.

You have in your plans that you combine those 2 strings before it reaches the main panel - what breaker size is appropriate for that?
What wire size? Did you calculate with temperature derating if that wire is in conduit on the roof? (How far off the roof is your conduit?)

I think some AHJ are more toward helping contractors than homeowners

My experience is usually they like homeowners better and will be more helpful to them.

[sdold]

Hi GreenTeeCrazy: I did drawings for two Enphase M215 systems in CA that passed two different AHJs without much trouble, they are in Autocad and PDF form, if you'd like to use them for ideas give me your email address and I'll send them to you.

I think the building dept.'s willingness to work with you depends a lot on how hard they have to work to figure out the drawings, and how much of what they need is missing, so I think you're on the right track.

[GreenTeeCrazy]

@foo1bar,

Correct, the the wires from string 1 and 2 get combined in midnite w/2 20 A breakers, then connect to MainPanel w/20 A double pole backfeed breaker

@sdold;
PM sent, anything can help Thank you

I totally agree, My drawing were not explained properly

[sensij]

@foo1bar,

Correct, the the wires from string 1 and 2 get combined in midnite w/2 20 A breakers, then connect to MainPanel w/20 A double pole backfeed breaker

Foolish comments like this are probably why the inspector you talked to is not interested in looking at plans produced by someone not qualified to make them. I'm not sure which fundamental you are missing, but somehow you are not grasping one of the following:

1) Microinverters produce 240 V power
2) 240 V power in the US has two hot legs, 180 deg phase difference
3) All hot legs must have over current protection.
4) A double pole breaker can be used to protect a circuit with two hot legs, in this case, a single 240 circuit.
5) A 20 A double-pole breaker is rated for use on circuits which carry up to 16 A (80% of 20A = 16A)
6) The full current flows through both legs at any moment in time.
7) When you combine two parallel circuits, the currents add together.
8) Each string requires its own two pole breaker when you combine them. If you were planning on using only two single pole breakers in your combiner, that would also be wrong. There would be 4 hot legs, but only two would be protected.
9) The breaker going into your main service panel needs to rated for the combined current. In this case, you need at least a 25 A two pole breaker, and your conductors need to be large enough to be protected by that.

[GreenTeeCrazy]

Today was a WOW day.
I talked again to the inspector and what a totally different person he was. day and night!

He spent more time explaining to me the whole process on how the drawing should look like, he actually made copies for me to follow!!!
Then he called the building inspector to explain to me what is needed from me to show them, like wind and snow loads. most of that info
is found at ironridge website.

I shook their hand and thanked them for the help that they provided me with.

Amazing experience.

Now back to the drawing table.

P.S. steve, your drawings are coming handy indeed

[J.P.M.]

Hi J.P.M., thatns for your comment.
I actually did contacted the town and they have no clue to what is required from a homeowner diy solar installation, they always had contractors doing
the work for the homeowners. as i said before, i do my own repair, upgrade in my home, water heater, gas line, boiler, driveway, fence, generator and so on.
and i always apply for permits and have my work inspected by the AHJ inspector. My famil's safety is my first priority.

I do have more building drawing but in different pc, and i dont have access to them right now. but i did all the calculation for wind, snow load, rafters spacing and more diagrams on setbacks from gutters etc.

I just want to make sure that is the inspector denies my application is because of valid point but not that i didnt hire a PE for their seals and stamps.

sensij, thanks for your input.

For my part, you are most welcome. Seems like you got religion.

[samotlietuvis]

Vow, that’s unbelievable experience for you.

Went for the 2nd time to the permit office, I they “failed” me for missing solar panel installation copy that was actually there. I showed it to the guy. He looked at it and told me to come back tomorrow.

Don’t forget to tell your permit guy what a great service he does to your city.

Today was a WOW day.
I talked again to the inspector and what a totally different person he was. day and night!

He spent more time explaining to me the whole process on how the drawing should look like, he actually made copies for me to follow!!!
Then he called the building inspector to explain to me what is needed from me to show them, like wind and snow loads. most of that info
is found at ironridge website.

I shook their hand and thanked them for the help that they provided me with.

Amazing experience.

Now back to the drawing table.

P.S. steve, your drawings are coming handy indeed

[tehan]

I've just been through this process myself, though in a much easier jurisdiction. My view is what you have looks pretty good. I don't normally disagree with Sensij who bats close to 1.000, but the M250 has a maximum output of 1A and you have 18 of them so I think you are fine with a 20A breaker. You are missing a few things that I believe will generally be required: (1) datasheets for your panels, inverters, and rails and (2) calculations of wire ampacity and structural loading (The Ironridge webstie has a great tool that will provide you with all the calculations you need). Good luck!

[foo1bar]

I've just been through this process myself, though in a much easier jurisdiction. My view is what you have looks pretty good. I don't normally disagree with Sensij who bats close to 1.000, but the M250 has a maximum output of 1A and you have 18 of them so I think you are fine with a 20A breaker.

Nope - need to multiply 18A by 1.25 because of NEC requirements - I think it's because it's a "continuous" current - would have to look it up.

Here's an article with NEC code references:

http://www.smainverted.com/2015/02/17/properly-sizing-a-pv-inverter-breaker/

[sensij]

I've just been through this process myself, though in a much easier jurisdiction. My view is what you have looks pretty good. I don't normally disagree with Sensij who bats close to 1.000, but the M250 has a maximum output of 1A and you have 18 of them so I think you are fine with a 20A breaker. You are missing a few things that I believe will generally be required: (1) datasheets for your panels, inverters, and rails and (2) calculations of wire ampacity and structural loading (The Ironridge webstie has a great tool that will provide you with all the calculations you need). Good luck!

Yeah, I definitely don't bat 1.000, but this one is a hanging curve.

Nope - need to multiply 18A by 1.25 because of NEC requirements - I think it's because it's a "continuous" current - would have to look it up.

Here's an article with NEC code references:
http://www.smainverted.com/2015/02/1...erter-breaker/

This is right. Once you get up to commercial scale (>125 A), there are actually breakers that are rated for continuous load circuits at 100% of nameplate, and code has an exception that allows those to be used without the 1.25 factor. See this white paper for a primer.

[tehan]

Yeah, I definitely don't bat 1.000, but this one is a hanging curve.



This is right. Once you get up to commercial scale (>125 A), there are actually breakers that are rated for continuous load circuits at 100% of nameplate, and code has an exception that allows those to be used without the 1.25 factor. See this white paper for a primer.

Checked and you are right. Dang, 1.000 it is. Kinda odd though, because derating a breaker is more about nuisance prevention than safety so you wouldn't necessarily think it should be a requirement. Mind you, I've seen enough people fix a frequently tripping fuse with a nail to know that a nuisance can easily become a hazard!

[GreenTeeCrazy]

Thanks everyone, I am still working on it. all tips are welcome.

@sensij,
9) The breaker going into your main service panel needs to rated for the combined current. In this case, you need at least a 25 A two pole breaker, and your conductors need to be large enough to be protected by that.

I got what you are saying here. Thanks

[Smitty]

GreenTee, I just came from my building permit dept here in MD. Here I must have a building permit for mounting the array first, then the electrical permit after the first permit is approved. They did mention the 3 feet perimeter if, heaven forbid, there is a fire and the firefighters need to walk on the roof. I will be stealing your drawings to help with mine . I too do EVERYTHING on my property and have it approved by my licensed friends for the respective discipline. I sure do learn a lot that way and it keeps the County (who by the way is extremely helpful) happy. Thanks!

[GreenTeeCrazy]

@samotlietuvis,
So true, I am getting a very positive attitude from my town inspector.

[GreenTeeCrazy]

GreenTee, I just came from my building permit dept here in MD. Here I must have a building permit for mounting the array first, then the electrical permit after the first permit is approved. They did mention the 3 feet perimeter if, heaven forbid, there is a fire and the firefighters need to walk on the roof. I will be stealing your drawings to help with mine . I too do EVERYTHING on my property and have it approved by my licensed friends for the respective discipline. I sure do learn a lot that way and it keeps the County (who by the way is extremely helpful) happy. Thanks!

please help yourself to my drawing but be careful as i have too many mistakes in their.

In my town, we need 2 permits, 1 for zoning dept and 1 for building, I'll find out about the 3 feet setback once i file the building permit.

Its always nice to have a friend who has some licenses