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Thread: 80 amp AC breaker for large guage wire

  1. #1

    Default 80 amp AC breaker for large guage wire

    My inverters (parallel outback 2012's) are supplying AC power to three separate buildings: a garage, a guest house, and main house. I'm currently using a Square-D QO panel to distribute power from the inverters to the guest house and garage sub panels.

    My main house is under construction and nearly completed. The wire run to the main house is about 130 feet from the distribution panel and will require large guage wire (2/0). I'm having difficulty finding circuit breakers with lugs that will accept larger than #2 wire. I need to find a 60 amp breaker that will accept 2/0 wire, or a method to use a standard 60 amp breaker to supply 2/0 wire.

    Any suggestions were to find 60 or (80 amp) AC circuit breaker that will accept 2/0 wire? I would prefer something compatable with Square-D, but if there's no choice, I can change out the distribution panel to another brand that has the breakers I need.



    Thanks.
    Off grid 3.6 Kw solar, 2968Ah AGM's, Outback combiners, 4 FM80's, parallel FX2012's, Midnight solar E-Panels, Hub, Mate, Trimetric, Generac 14kw backup generator.

  2. #2
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    Default Re: 80 amp AC breaker for large guage wire

    Guess I'm curious WHY you want to run 2/0 ?

    The most two 2,000w inverters will put out is 33amp@120v

    130' /120v/34amp using #2 alum = 2% voltage drop......switch to copper, and it's 1.2%

    Get a Hub, and set up your two inverters as master/slave, put out true 240v, and you could cut the above in half again.

    Is there more to the story ?
    20-175watt Solarworld panels, mounted on two home built single axis powered trackers, 10-245w Solarworld panels, mounted on home built dual axis tracker, 1 MX60, 1 FM60, 1 FM80, 24v bank of Absolyte 2v AGM GNP II cells 1200amp/hr, 2-GTFX2524 2500w Outbacks producing 120/240 AC, Trimetric monitor, Grid tied, produce about 600kw/hrs/mo. 12/2012: Added 10 Solarworld 255w panels and 10 Enphase mirco inverters.

  3. #3
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    Default Re: 80 amp AC breaker for large guage wire

    using 2/0 wire is insane unless you got it for free. As already posted the losses using copper and #2 is insignificant and when you consider that its very unlikely the inverters will be supplying more than about 80% most of the time makes it even less of a concern.

  4. #4

    Default Re: 80 amp AC breaker for large guage wire

    I have no desire to use 2/0 wire, believe me. I was just going by the instructions that state: "All AC wiring from the AC source and to the AC loads must collectively handle 120 amps or more." Obviously I'm not completely understanding something. So...basically for two parallel 2012 inverters, the max output I can expect is 33 amps at 120 volts, and I should wire accordingly? That would make me a much happier person and save a ton of $$
    Off grid 3.6 Kw solar, 2968Ah AGM's, Outback combiners, 4 FM80's, parallel FX2012's, Midnight solar E-Panels, Hub, Mate, Trimetric, Generac 14kw backup generator.

  5. #5
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    Default Re: 80 amp AC breaker for large guage wire

    It sounds like that is a requirement for the Main Drop from the power pole requirement. Is there ever a chance that the home will have utility power?

    If so, get a regular AC Main panel (which will accept 2/O wire) and wire up the inverters as branch circuits with standard 20 amp breakers (or whatever make sense for your needs). Leave the main meter blank on the panel (that will confuse the heck out of every one).

    For voltage drop--using a generic voltage drop calculator:

    • 120 volts, 3% maximum voltage drop (3.6 volts), 33 amps -> 4 awg @ 33 amps and 130 feet (one way run) gives 2.6 volt drop


    The above assumes that you want 100% of the maximum current available 130 feet away. Obviously, if you need less current (say 15 amp branch circuit), you could use smaller gauge wire.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  6. #6
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    Default Re: 80 amp AC breaker for large guage wire

    Quote Originally Posted by Bigwooo View Post
    I have no desire to use 2/0 wire, believe me. I was just going by the instructions
    Whose instructions ?

    Quote Originally Posted by Bigwooo View Post

    So...basically for two parallel 2012 inverters, the max output I can expect is 33 amps at 120 volts, and I should wire accordingly?
    Yep.

    AND like I said, buy an Outback Hub, and the two inverters can be set up to produce 240, and you can get by with #6 copper.....cause that's exactly what I'm doing over about the same distance.

    Then, when you get it to the panel in the house/garage/etc, you split the two wire 240 onto separate bus bars in the panel, and pick up 120v off either......PLUS you have 240v should you need it for something ( like a well pump ).
    20-175watt Solarworld panels, mounted on two home built single axis powered trackers, 10-245w Solarworld panels, mounted on home built dual axis tracker, 1 MX60, 1 FM60, 1 FM80, 24v bank of Absolyte 2v AGM GNP II cells 1200amp/hr, 2-GTFX2524 2500w Outbacks producing 120/240 AC, Trimetric monitor, Grid tied, produce about 600kw/hrs/mo. 12/2012: Added 10 Solarworld 255w panels and 10 Enphase mirco inverters.

  7. #7

    Default Re: 80 amp AC breaker for large guage wire

    Thanks TnAndy & BB. I do have a hub as it's required for a parallel configuration also. I don't really anticipate the need for 240 volts and I'm supplying power to three buildings: A main house, guest house, and garage/workshop. I'd like to keep the available amps higher in case I'm using power in the shop while both houses are occupied.

    Even though the max amp output in parallel is 33 amps or so, I don't understand why the instrucions on page 28 for the FX inverter state that the wiring capacity must equal 60 amps. Maybe it is a requirement for the Main Drop from the power pole, but I'll never be grid tied so that's not an issue. That 60 amp figure is why I was planning to use the larger guage wire.

    I think I'll use the 33 amp figure for calculating wire size. You just saved me a lot of $$....thanks.
    Off grid 3.6 Kw solar, 2968Ah AGM's, Outback combiners, 4 FM80's, parallel FX2012's, Midnight solar E-Panels, Hub, Mate, Trimetric, Generac 14kw backup generator.

  8. #8
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    Default Re: 80 amp AC breaker for large guage wire

    Quote Originally Posted by Bigwooo View Post
    I do have a hub as it's required for a parallel configuration also. I don't really anticipate the need for 240 volts and I'm supplying power to three buildings: A main house, guest house, and garage/workshop. I'd like to keep the available amps higher in case I'm using power in the shop while both houses are occupied.
    1. That's not a lot of power to run 2 houses and a shop on to begin with.

    2. By going to 240, you don't "loose" any amps.....you merely split them between 2 legs of 120v.....means each wire can carry 1/2 the amp load of a single 120v wire, meaning you get to downsize the wire even more......AND, as a bonus, probably have less voltage drop.

    Just wanting to make sure you understand that clearly, as I sensed some confusion in your answer....or, maybe, my understanding of your answer...Quien Sabe ? ........ahahahaaa
    20-175watt Solarworld panels, mounted on two home built single axis powered trackers, 10-245w Solarworld panels, mounted on home built dual axis tracker, 1 MX60, 1 FM60, 1 FM80, 24v bank of Absolyte 2v AGM GNP II cells 1200amp/hr, 2-GTFX2524 2500w Outbacks producing 120/240 AC, Trimetric monitor, Grid tied, produce about 600kw/hrs/mo. 12/2012: Added 10 Solarworld 255w panels and 10 Enphase mirco inverters.

  9. #9
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    Default Re: 80 amp AC breaker for large guage wire

    As Andy says--If your loads are not 33 amps of 120 VAC going to one machine but, for example 20 amps going to two or more units and you can balance the loads across a 120/240 VAC circuit--It would be much less copper/voltage drop.

    Regarding 60 amps--Most inverters can surge 2x of their rated power for a few cycles to 10 minutes or more--It is possible that these inverters will supply several minutes of 2x rated current.

    Also, remember if you have motors with poor power factor, it is possible that the inverters VA rating (volts*amps) is higher than it power rating (volts*amps*power factor)--Which would also dictate larger wire (PF of 0.6 for induction motors is not unusual). Wiring/breakers should be rated for V*A usage with alternating current.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  10. #10

    Default Re: 80 amp AC breaker for large guage wire

    The instructions refer to how to wire it for the full rated capacity of the pass-through circuit.

    The NEC allows inverters to feed a circuit with a higher rating than the inverter can produce. This allows fairly small inverters to provide back-up power to loads which are usually fed by a larger source. (ie. utility or generator)

    Outback FX inverters have a 60 amp internal transfer switch regardless of the inverter's rated output. (The Mobile versions specify a 30 amp circuit.)
    A 60 amp AC load panel can hold several typical residential branch circuits. Especially if it is a 120/240 vac subpanel.

    The NEC article 230 requires that the minimum size for overhead and underground service conductors be a minimum of #8 copper or #6 aluminum. I have found building departments and inspectors who have interpreted this to serve as a mimimum service entrance rating. I've also had the AHJ (authority having jurisdiction) require that all residences have a metered service entrance with a minimum 60 amp breaker and circuit size.

    For off grid, as far as function is concerned, it needs to be rated for the maximum available power which is not always obvious. You may think your wire may have to be sized at 125% of your largest source. Beware. The inverters by the company-formerly-known-as-Trace can actually add the inverter's output to the generator (or grid) output and exceed the rating of either.
    Last edited by SolaRevolution; February 25th, 2012 at 9:07 PST.

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