breaker sizing

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jtdiesel65
jtdiesel65 Solar Expert Posts: 242 ✭✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
I want to provide a method for creating a bypass to switch from inverter power to generator power and I have to keep the neutrals isolated. This means I need a switch or breaker for the neutrals. The system is two 240v two phase inverters each with a 30a dual pole output breaker. The neutral outs from each inverter go to common bus bar. I would install the breaker between this common bus and the bus that feeds the house. I'm thinking that if I use a breaker for the neutral, I would need a 120a breaker to match the 30 amps on each leg of each inverter. 2 inverters * 2 legs each *30a each leg =120a. That correct?

thx
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: breaker sizing

    Why do you need to switch the neutrals? Usually that is not a problem. The only time it is would be if there were an N-G bond issue.

    There's no such thing as a "two phase" inverter. There's single phase, which is 240 VAC 60 Hz in NA and usually has a center tap neutral on the output, there's "half phase" 120 VAC 60 Hz where one side is connected to ground to be neutral (or all left floating for most MSW types), and there's 3 phase which is an animal you probably won't be dealing with (two different pole Voltage choices and configurations, usually three separate inverters tied together).

    Are these two SW4024 inverters stacked? Normally the gen would feed AC IN on such a unit. If you need to bypass the inverters altogether that requires a transfer switch.

    Please provide more detail about the equipment in question and what the usage is. As stated your inquiry doesn't make sense.
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  • jtdiesel65
    jtdiesel65 Solar Expert Posts: 242 ✭✭✭
    #3
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    Re: breaker sizing

    They are split phase: http://www.solar-electric.com/schneider-electric-sw-conext-inverter-4024-120.html

    The input neutrals have to be isolated from output neutrals when they are stacked. The AC panel advertises bypass capability but unfortunately doesn't provide the correct parts given that the neutrals need to be isolated. It's an oversight by Schneider. What I'm really after is a sanity check on the size of the breakers required to switch the neutrals.

    thx
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: breaker sizing

    Ah, Xantrex: the reason why there's Outback and MidNite. ;)

    When you split a 240 VAC 30 Amp circuit the maximum power between one leg and neutral is 30 Amps. If power is supplied from the other leg as well the current on the neutral line is the difference i current between the two legs (which are 180 degrees out of phase). So there is never more than 30 Amps on the neutral line.

    Examples:

    L1 = 30 Amps
    L2 = 0 Amps
    N = 30 Amps

    L1 = 30 Amps
    L2 = 10 Amps
    N = 20 Amps
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #5
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    Re: breaker sizing

    Hi jt..,

    There will be less confusion if your Signature states that your inverters are Context SW4024s. For almost two decades Trace and Xantrex made SW4024s, and this can either confuse many of us, OR we often feel the need to ask this question before replying.

    Schneider, using Divine wisdom, has not differentiated their new inverters, from the tens of thousands of the older ones with the same model number.

    So the AC conduit box came from Schneider, and it lacks the correct handling of the Neutrals?

    You might go to the MidNite Forum, and ask the question of how to handle this situation in the e-panel Topic, perhaps:
    http://midniteforum.com/index.php?board=4.0

    It would seem that this Bypass Breaker assembly MUST have all breakers Ganged together. Perhaps MN's panel will have the correct solution and, if the Schneider (?) box is missing something that is a MUST, then it may be unsuitable for the task, and needs to be returned ... ??

    Seemed to me that some of these Stacked Context Inverters were BURNING UP in the field ... this must have been the cause?

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: breaker sizing
    Vic wrote: »
    Hi jt..,

    There will be less confusion if your Signature states that your inverters are Conext SW4024s. For almost two decades Trace and Xantrex made SW4024s, and this can either confuse many of us, OR we often feel the need to ask this question before replying.

    Schneider, using Divine wisdom, has not differentiated their new inverters, from the tens of thousands of the older ones with the same model number.

    I suspect that may not be by accident. The old SW inverters had a well-deserved reputation for quality. The XW series did damage to the Xantrex brand name. So now we change the name and keep the old model designation. Why? Perhaps to fool the public?

    It's not unheard of. There is a company using the name "Tracer" on products - perhaps to associate with the venerable Trace equipment?

    It's half a step above the practice of putting flashing diodes and the letters "MPPT" on a shunt controller to fool people into thinking they can get the real deal for hundreds less.

    You don't get cynical just because you get old, but being cynical to begin with can help you get old.
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #7
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    Re: breaker sizing

    Hi Marc,

    You are absolutely correct. I like to dislike Schneider Electric. I had thought that this model number choice might not be accidental -- wanting to have a more positive association from the old SWs with their new ones. This must work for Schneider, or perhaps just more defective thinking on their part.

    But, I do realize for off-gridders there are few alternatives to either the XW or SW inverters (yea, know about Outback). When any of the SW+es here croak, it will be a sad day, and wonder what one would do ... am holding out for a MidNite Inverter ... Thanks for the perspective, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • jtdiesel65
    jtdiesel65 Solar Expert Posts: 242 ✭✭✭
    #8
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    Re: breaker sizing

    I was one of the people having inverters fry. see: http://forum.solar-electric.com/showthread.php?21344-Fried-conext-sw4024

    Yeah, the AC panel and stacking kit do not provide all the parts required for bypass functionity for stacked inverters.


    My old inverter was a trace sw4024. Rock solid. Still have it on a shelf in case these new inverters don't work out.
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