AC load center as a AC disconnect

Couldn't find anything in a search on my question here, but I have two sunnyboys, a 4000 and 5000, and am thinking about feeding the AC from each into a small AC load center with circuit breakers to combine the AC conductors from the 2 inverters (six wires/conductors) to 3 wires (L1, L2 and N) which will go into the main AC box for our home. This instead of box with the handle on the side that is unfused. The breakers would be the "handle". I think the breakers would also function as backfeed breakers to protect the inverter from utility backfeed. Inside my main AC load center for the home I was going to still use circuit breakers to snap in and connect the 120V on one side, the other 120V and the neutral would screw into the neutral bus bar as I don't have anywhere other than a CB to connect the AC coming from the inverters. I know it is redundant to have two sets of CB on the AC output side of the inverter. Do most of you guys just buy the AC disconnect unfused with the handle on the side and then connect to a couple of circuit breakers into your house AC load center? I have been reading some people are using small (A few circuit breakers) AC load centers as AC disconnect devices which also protect the inverters. Opine welcome and thanks.

My Grid tie system:
28 Solarworld 255W panels. 2 strings of 10 each into the SB5000 and 1 string of 8 into the SB4000.

Comments

  • solar_davesolar_dave Solar Expert Posts: 2,384 ✭✭✭✭
    Re: AC load center as a AC disconnect

    That is how my 2 PVP5200 are wired but the AHJ also required the disconnect switch before it entered the main panel (with the proper sized backfeed breaker) so it could be clearly labeled as a single point of disconnect..
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: AC load center as a AC disconnect
    solar_dave wrote: »
    That is how my 2 PVP5200 are wired but the AHJ also required the disconnect switch before it entered the main panel (with the proper sized backfeed breaker) so it could be clearly labeled as a single point of disconnect..

    This is what you have to watch out for: the Authority Having Jurisdiction.

    Otherwise so long as one proper over-current protection device (i.e. circuit breaker) is in place there is not any need for a separate AC disconnect. It's not like you have to turn these things off and on every day. :roll:
  • DanS26DanS26 Solar Expert Posts: 247 ✭✭✭
    Re: AC load center as a AC disconnect

    You might want to check and read carefully your interconnect agreement with your utility. Many of these agreements clearly state that the AC disconnect be of the blade style so that a VISUAL disconnect is observed by utility and safety personnel.
    23.16kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring with PVOutput.org
  • DanS26DanS26 Solar Expert Posts: 247 ✭✭✭
    Re: AC load center as a AC disconnect
    michaelc wrote: »
    ....... for the home I was going to still use circuit breakers to snap in and connect the 120V on one side, the other 120V and the neutral would screw into the neutral bus bar ........

    That sounds like wiring a dead short to me.
    23.16kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring with PVOutput.org
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: AC load center as a AC disconnect

    I sort of assumed he just wrote that wrong. Maybe I shouldn't have? There is a suspicion of lack of coordination with the utility and local inspectors here as a design should need to be submitted and approved before any equipment is purchased or installed.
  • michaelcmichaelc Solar Expert Posts: 36
    Re: AC load center as a AC disconnect
    I sort of assumed he just wrote that wrong. Maybe I shouldn't have? There is a suspicion of lack of coordination with the utility and local inspectors here as a design should need to be submitted and approved before any equipment is purchased or installed.
    , but

    No, your right, I have not got the utility involved yet, I just submitted their package to them which is a few signed agreements and a drawing. Same thing the inspection folks want. They do specify the type of meter housing, DC connect specs, but no specs on AC disconnect, just a clearly labeled point, lockable by them, of disconnection from their grid, but I suppose If they needed to shut things off, a handle would make things easy and quick. As to wiring the system into our house main panel. I was going to ask them exactly how that is accomplished. I read a couple of circuit breakers, one for the side of the panel fed by the utility red wire, one for the other side fed by the black wire and then white. The AC wires coming out of the inverter are orange, red and white and labeled L1, L2 and N. I assume the L1 is the red in the main service panel and L2 is black and N is the white neutral or vice versa. What was confusing to me was the physical connection from the AC disconnect to the main service panel, which would be 3 wires...L1, L2 and N since it is 220 volts, L1 (110V) would be connected to a 30 amp breaker (max) pushed into a spare slot on one side of the panel, L2 (110V) would be connected to a 30 amp breaker pushed in to the slot opposite the first 30 amp breaker and the white N would be screwed into the bus bar with all the other white wires assuming their is a hole for it, have not looked. Will see what the utility says. I cant install anything until they come over for a pre inspection first. As for L1 and L2 colors, I read L1 is usually red and L2 is black here in the US.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: AC load center as a AC disconnect

    You're using an inverter or inverters with 240 VAC output. As such both 'hot' leads need to be switched off/disconnect simultaneously using a double-pole 240 Volt breaker. These are L1 and L2. The N is Neutral and needs to be connected to the main service neutral bus. There is no need to disconnect this with either a breaker or a switch as it is bonded to ground and has zero Voltage potential in that respect.

    The disconnect requirement is an additional and unwarranted nuisance which will require the output of the inverter(s) to go outside to another box with the big ol' knife switch in it so the utility can shut it off. This makes no sense as disconnecting power to the house will shut down the GTI anyway, and there's no reason why they should need to kill your solar separately. Some people just do not understand the nature of anti-islanding. Unfortunately that includes a lot of people who make the rules.

    The pre-inspection is probably necessary as you can not connect just any size GTI to any service panel; there has to be "room" for it electrically (NEC 120% back-feed regulation).
  • DanS26DanS26 Solar Expert Posts: 247 ✭✭✭
    Re: AC load center as a AC disconnect

    A 30 amp double pole breaker is probably not going to satisfy the back feed NEC requirements for the two inverters you listed when combined.

    You should consider employing a licensed electrician to make sure all the devices, wiring and connections are compliant to code. It can get complicated.
    23.16kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring with PVOutput.org
  • michaelcmichaelc Solar Expert Posts: 36
    Re: AC load center as a AC disconnect
    DanS26 wrote: »
    A 30 amp double pole breaker is probably not going to satisfy the back feed NEC requirements for the two inverters you listed when combined.

    You should consider employing a licensed electrician to make sure all the devices, wiring and connections are compliant to code. It can get complicated.

    Good advice....it is complicated...somewhat. I agree about all the disconnect boxes the utility wants. They have no way to shut off utility power in our house except to open the main service panel and click off the breakers, which is what I want to do with my small AC load center box that holds 4 breakers that would accept the double throw units which I planned on putting the L1 and L2 wires from the inverter into then running a 10amp 4 wire conductor to the main service panel. The utility solar rep here is really helpful and sends me links to all their guides for contractors and rules.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: AC load center as a AC disconnect

    Utilities usually just pull the meter if they want your power off. If they can't do that they can clip the wires.
  • DanS26DanS26 Solar Expert Posts: 247 ✭✭✭
    Re: AC load center as a AC disconnect
    michaelc wrote: »
    Good advice....it is complicated...somewhat. I agree about all the disconnect boxes the utility wants. They have no way to shut off utility power in our house except to open the main service panel and click off the breakers, which is what I want to do with my small AC load center box that holds 4 breakers that would accept the double throw units which I planned on putting the L1 and L2 wires from the inverter into then running a 10amp 4 wire conductor to the main service panel. The utility solar rep here is really helpful and sends me links to all their guides for contractors and rules.

    You probably mean #10 "gauge" wire. But again based on the description of your system that size wire would most likely be under sized from the AC combiner panel to the main distribution panel. I'd still recommend you hire a professional.
    23.16kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring with PVOutput.org
  • bill von novakbill von novak Solar Expert Posts: 891 ✭✭✭✭
    Re: AC load center as a AC disconnect
    Utilities usually just pull the meter if they want your power off. If they can't do that they can clip the wires.

    The last time we got power turned on it was odd to watch. The utility worker came out, did a quick inspection, got on her phone and said "OK turn on 18448." About 30 seconds later power came on.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: AC load center as a AC disconnect
    The last time we got power turned on it was odd to watch. The utility worker came out, did a quick inspection, got on her phone and said "OK turn on 18448." About 30 seconds later power came on.

    That's something else they can do with smart meters.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: AC load center as a AC disconnect

    Sunnyboy 4000 lists its maximum output current as 17 Amps (at 240 VAC). Therefor it could be wired with 12 AWG but probably should be 10 AWG as the breaker would need to be 30 Amp.

    Sunnyboy 5000 lists its maximum output current as 21 Amps (at 240 VAC) so again you're looking at 10 AWG and a 30 Amp breaker.

    The combination of the two is 38 Amps, pretty close to the 40 Amp maximum for a standard 200 Amp service. And if the AHJ goes by the breaker size (60 Amp total) there will be an argument.

    This is why professional installers can be a good idea.
  • michaelcmichaelc Solar Expert Posts: 36
    Re: AC load center as a AC disconnect
    Sunnyboy 4000 lists its maximum output current as 17 Amps (at 240 VAC). Therefor it could be wired with 12 AWG but probably should be 10 AWG as the breaker would need to be 30 Amp.

    Sunnyboy 5000 lists its maximum output current as 21 Amps (at 240 VAC) so again you're looking at 10 AWG and a 30 Amp breaker.

    The combination of the two is 38 Amps, pretty close to the 40 Amp maximum for a standard 200 Amp service. And if the AHJ goes by the breaker size (60 Amp total) there will be an argument.

    This is why professional installers can be a good idea.


    Yep, this is a good idea. I may just hook up the 5000 and leave the 4000 for later. My intent was to use the 4000 later to add off grid capability. Thanks for all the input.;)
  • michaelcmichaelc Solar Expert Posts: 36
    Re: AC load center as a AC disconnect
    michaelc wrote: »
    Yep, this is a good idea. I may just hook up the 5000 and leave the 4000 for later. My intent was to use the 4000 later to add off grid capability. Thanks for all the input.;)

    Just received a copy of the 2014 NEC. Going to try to digest PV sections. May be a waste of a hundred dollars.
  • DanS26DanS26 Solar Expert Posts: 247 ✭✭✭
    Re: AC load center as a AC disconnect
    michaelc wrote: »
    Just received a copy of the 2014 NEC. Going to try to digest PV sections. May be a waste of a hundred dollars.

    You are a true DIY'er. Studying the NEC code is neither a waste of time or money. Good luck on your project.
    23.16kW Kyocera panels; 2 Fronius 7.5kW inverters; Nyle hot water; Steffes ETS; Great Lakes RO; Generac 10kW w/ATS, TED Pro System monitoring with PVOutput.org
  • michaelcmichaelc Solar Expert Posts: 36
    Re: AC load center as a AC disconnect
    DanS26 wrote: »
    You are a true DIY'er. Studying the NEC code is neither a waste of time or money. Good luck on your project.
    p
    Here is a good article on adding AC from your inverters to the service panel and how 100 or 200 amp service affects. Attachment not found. Mike
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