Subpanel and ac disconnect

I apologize for a repeated question....I have done the calcs and am now seeing numbers appear that weren't there before ...LOL


I have 2 200A panels in the house, with brkrs for each located next to meter.
I installed a 125A subpanel strictly for solar at the back of the house next to meter. I have 2 SMA7000's feeding the subpanel using 2p 40 brkrs.
I also figured I would need a 100A 2p AC disconnect.

I will run #4awg from inverters at array 180' to subpanel and then switch to #6awg to wire sub to ac disconnect.

Math formulas seem to work ok, and I have done string sizing and temp calcs. Just want to make sure before ordering equipment. Good to get second opinion.

Anyone see any issues with this?

Comments

  • RCinFLARCinFLA Solar Expert Posts: 1,284 ✭✭✭
    Re: Subpanel and ac disconnect

    Might be better if you put together a little diagram showing all the wire sizes and lengths.

    If you have 100 amp breaker to subpanel you need #4 feed, not #6.

    With two 40 amps feeding subpanel that is 80 amps of the 125 amp panel rating. With 20% overage allowance (150 amps) that would allow a 60 amp breaker feed to main box, not 100 amp. #6 would be okay in that case but you might have a bottleneck if your two inverters can produce more then 60 amps to main box for grid backfeed.

    The 200 amp main panel feeds from subpanel depends on grid breaker size. You can not use a 200 amp breaker anymore with 80 amp (or 60 amp) backfeed from solar.

    Rule is you are allowed 20% overage to panel rating summing all potential incoming power feeds. (grid input + solar input)

    You should be fine with two 30 amp breakers from inverters. That would allow a 75 amp breaker to subpanel. A 60 amp breaker would allow you to use #6 wire to main.

    I am not sure about rules on subpanel used only as junction box with no branch loads installed. I think if the subpanel has space for branch loads, even if not used, you get held to the two input power summation. Alot depends on the local inspector and their knowledge (or lack of) of solar setups. It is always good to review the plans with local inspectors prior to install to get their suggestions. It avoids some pain later.
  • stumpy40stumpy40 Solar Expert Posts: 35
    Re: Subpanel and ac disconnect

    The 200A panels are located in the house.

    I'm tying the solar to a 125A subpanel using 2 40A breaker. The math works out ok when I do it...but wanted to check just in case.

    The inverter breakers are sized according to inverter specs.

    I wasn't aware I couldn't run 6awg to connect subpanel and ac disconnect. I saw that 6awg was good for that amperage.


    I'll try and upload my one line.....
  • RCinFLARCinFLA Solar Expert Posts: 1,284 ✭✭✭
    Re: Subpanel and ac disconnect
    stumpy40 wrote: »
    The 200A panels are located in the house.

    I'm tying the solar to a 125A subpanel using 2 40A breaker. The math works out ok when I do it...but wanted to check just in case.

    The inverter breakers are sized according to inverter specs.

    I wasn't aware I couldn't run 6awg to connect subpanel and ac disconnect. I saw that 6awg was good for that amperage.


    I'll try and upload my one line.....

    From your questions, I would guess you are doing this without a permit and inspection. In many places you can do your own work on your property without an electrician's license but installation still needs to be permitted, inspected, and be per code.

    Any grid-tie systen should have the county inspector go over plans.

    If you don't you will likely have problems with authorities.

    The power company will likely be the instigator if they see the PV panels when reading meter, or see an unusual change in your power consumption history triggering a power theft investigation. They will look up county records for permit and inspection. In your county you might even need power company to sign off on grid-tie system.

    Three major headaches can result.
    1) power company disconnects you from grid until equipment is removed and you pay reconnect fee.
    2) County fines you for not getting permit.
    3) Homeowner insurance drops you, or refuses to pay for any fire claims.

    NEC code summary for PV systems:
    http://www.lacleantech.net/download/pv-nec-v-1.9-opt.pdf
  • dreesdrees Solar Expert Posts: 481 ✭✭✭
    Re: Subpanel and ac disconnect
    stumpy40 wrote: »
    The 200A panels are located in the house.

    I'm tying the solar to a 125A subpanel using 2 40A breaker. The math works out ok when I do it...but wanted to check just in case.
    With a 200A service panel with a 200A main breaker, you can only backfeed 40A of solar (actually 32A because of NEC rules). There's no way you can backfeed 80A of PV unless you either upgrade your main panel or downsize your main breaker.
  • stumpy40stumpy40 Solar Expert Posts: 35
    Re: Subpanel and ac disconnect

    What if I have 2 200A panels? My house is a 400A service....I am getting assistance from a master electrcian. He is saying that I have a 400A service since I have 2 200A panels, and a meter that's rated for 400A.

    My issue is if he is correct in what he's telling me. Sometimes there is a doubt in my mind. Getting a second opinion from guys that know is perfectly within reason in my book.
    This house is in the middle of nowhere....no ispections, permitting...etc. just utility inspection. I call in my own meter read.

    125A sub with 2 40A would work wouldnt it?

    Another topic is AC disconnect...can't I just use 1 100A AC disconnect? Inverters to subpanel, subpanel to disconnect, disconnect to gutter then meter.

    Isnt the AC disconnect for utility purpose only....If it breaks power between utility and solar. Isn't that the point. Master says I need 2 100A disconnects because they will be wired in between inverters and panel....according to numerous drawings I have seen this is not the case. They are wired after panel between meter.

    Should I have gotten a company to do this....maybe. I'm to far into it now, I can do this. I might have questions, but I am determined to learn and get it right.
  • RCinFLARCinFLA Solar Expert Posts: 1,284 ✭✭✭
    Re: Subpanel and ac disconnect
    drees wrote: »
    With a 200A service panel with a 200A main breaker, you can only backfeed 40A of solar (actually 32A because of NEC rules). There's no way you can backfeed 80A of PV unless you either upgrade your main panel or downsize your main breaker.

    Residential (non-commercial) property can go 120% of panel bus rating. For 200 amp service panel he can tap in maximum of 40 amp breaker feed.

    If branch loading allows, the main breaker can be dropped to 150 amps then allowing a maximum of 90 amps PV insertion feed.

    Other option is to go straight to meter side grid connection with PV box, thereby bypassing the 200 amp service panel. You will have to get a licensed electrician to do this since pulling of meter is required.

    I really think with the 7000 watt inverter you will be fine with 30 amp breakers. Which would open up another option, although somewhat mickey mouse, to inject 30 amp breaker into each of the 200 amp panels, one inverter feed to each panel.

    For info, the reasoning is the panel could have the grid breaker amperage plus the PV system amperage total on the panel bus bars allowing branch breaker loads to draw over the bus rating current.

    With two 200 amp panels, I assume your house is somewhat of a mansion, with associated value. Without a permit/inspection you run risk with your homeowners insurance if, god forbid, you ever have a fire.
  • stumpy40stumpy40 Solar Expert Posts: 35
    Re: Subpanel and ac disconnect

    Hardly a mansion....3400sqft. Talk to the architect and GC it was their call. Price wise it wasn't a big deal over standard 200A service. It's not like it will ever be used up. They had a good reason, I just don't recall what it was. Long time ago

    7000's state 29A AC max output...30A is to small is it not? Just in case

    Can't use 200A panels....they are located in the house. Conduit runs would not work.

    I don't see where in the code or NEC that a 125A subpanel with 2 40A brkrs is not allowed if house main is 400A feeding 2 200A panels.

    There will not be a fire....come on now. This isn't a duct tape type job
  • stumpy40stumpy40 Solar Expert Posts: 35
    Re: Subpanel and ac disconnect

    You do bring up something interesting though...

    If the meter and gutter are outside and there are 2 200A brkrs/disconnects....isn't installing a subpanel and ac disconnect outside bypassing the panels anyway?

    Here is a pic of outside wall....technically I'm not going through 200A panels....am I wrong here.

    Imagine....125A sub installed to right of gutter and AC disconnect to the right of that.
    Inverters wired into sub...then to panel then to 2p AC disconnect....the to gutter feed....
  • RCinFLARCinFLA Solar Expert Posts: 1,284 ✭✭✭
    Re: Subpanel and ac disconnect

    You are fine if going directly into output of meter. You threw me off mentioning the two 200 amp service panels.

    Doing a tap off on 4/0 lines is not the easiest thing to do. You already have two branches off to your two panels.

    As to fire, it doesn't have to necessarily relate to being caused by your installation for the insurance company to balk at claim.
  • dreesdrees Solar Expert Posts: 481 ✭✭✭
    Re: Subpanel and ac disconnect
    stumpy40 wrote: »
    I don't see where in the code or NEC that a 125A subpanel with 2 40A brkrs is not allowed if house main is 400A feeding 2 200A panels.
    As said before - if you want to maintain NEC codes, you can't feed more than 125% of of the panels rating. So if you have a 200A rated panel with a 200A main breaker, you can only feed 40A of PV into the panel.

    If you downsize the breaker to 160A or smaller, then you can feed 80A into the panel (and combine each of your 40A PV breakers into that one 125A panel before feeding one of the 200A panels).

    If you don't want to downsize the main breaker in either panel, you can feed 40A into each panel.

    The AC disconnect needs to tie in before it hits one or both of your load centers - so you'd need 2 if you are feeding both 200A panels or one if you are only feeding one 200A panel. The disconnects also typically need to be located near the meter with the appropriate labels. Your utility will tell you their exact requirements.

    Hope that clears things up. Not that complicated once you understand the logic.

    EDIT: Didn't see the last 2 posts - YES - if your 125A combiner panel feeds your AC disconnect which feeds into the gutter and meter directly - you're good. This is typically called a "line-side-tap" where you are tapping into the lines coming out of the meter before any load center panels.
  • stumpy40stumpy40 Solar Expert Posts: 35
    Re: Subpanel and ac disconnect
    RCinFLA wrote: »
    You are fine if going directly into output of meter. You threw me off mentioning the two 200 amp service panels.

    Doing a tap off on 4/0 lines is not the easiest thing to do. You already have two branches off to your two panels.

    As to fire, it doesn't have to necessarily relate to being caused by your installation for the insurance company to balk at claim.

    I'm sorry for the really bad explanation on my part. Should have shown wall at first.
    Thanks for the clarification. It will be on the output side of the meter.

    Thanks....I will have a master sign off before anything is turned on. I just want to do it myself. He will inspect and check it all. I'm buying material for this tomm. so just wanted to make sure.

    Do you see a problem with wiring only 1 ac disconnect? I know it can be done both ways and the master has said it was OK....what is your opinion?
  • stumpy40stumpy40 Solar Expert Posts: 35
    Re: Subpanel and ac disconnect
    drees wrote: »
    As said before - if you want to maintain NEC codes, you can't feed more than 125% of of the panels rating. So if you have a 200A rated panel with a 200A main breaker, you can only feed 40A of PV into the panel.

    If you downsize the breaker to 160A or smaller, then you can feed 80A into the panel (and combine each of your 40A PV breakers into that one 125A panel before feeding one of the 200A panels).

    If you don't want to downsize the main breaker in either panel, you can feed 40A into each panel.

    The AC disconnect needs to tie in before it hits one or both of your load centers - so you'd need 2 if you are feeding both 200A panels or one if you are only feeding one 200A panel. The disconnects also typically need to be located near the meter with the appropriate labels. Your utility will tell you their exact requirements.

    Hope that clears things up. Not that complicated once you understand the logic.

    EDIT: Didn't see the last 2 posts - YES - if your 125A combiner panel feeds your AC disconnect which feeds into the gutter and meter directly - you're good. This is typically called a "line-side-tap" where you are tapping into the lines coming out of the meter before any load center panels.

    again I am really sorry for the confusion. Damn with my explanations. Pictures do wonders...LOL
  • dreesdrees Solar Expert Posts: 481 ✭✭✭
    Re: Subpanel and ac disconnect
    stumpy40 wrote: »
    Do you see a problem with wiring only 1 ac disconnect? I know it can be done both ways and the master has said it was OK....what is your opinion?
    No problem either way - since you have it combined into 1 125A panel, makes sense to use one AC disco between the meter and the panel.
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