Split phase or Single phase ?

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billybob9
billybob9 Registered Users Posts: 141 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
My new SMA Inverter is back feeding 120vac back into the grid with two hot wires (120vac ea ). Calling it 2 single phase (or poles) could possibly mean that it could be connected to either one of the 2 hot buses. Since I believe the Idea was to distribute the heat equally between the two buses then breaker slots next to each other, was a no brainer way to do it. So if power was going in instead of coming out it would be a 120/240VAC split Phase, but this never happens. 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,693 admin
    #2
    You have to check the inverter specifications, but it sounds like you are feeding 240 VAC back to your mains panel--Which is how virtually all of the US residential GT inverters are wired.

    Remember that almost all US modern homes are wired 120/240 VAC split phase. L1 to neutral is 120 VAC, L2 to neutral is 120 VAC. L1 to L2 is 240 VAC... L1 vs L2 are 180 degrees out of phase, so they "add up" to 240 VAC when used as power source.

    https://en.wikipedia.org/wiki/Split-phase_electric_power

    If you did not use L1 from first bus bar, and L2 from the second bus bar... (i.e., L1 from bar1 and L2 from bar2), you would get zero volts between the two connections.

    For standard two pole North American Breakers, L1 is Bar1 and L2 is Bar2 connections. So you always see 240 VAC between L1 and L2.
    Square D Homeline 30 Amp 2-Pole Circuit Breaker-HOM230CP - The Home DepotNote, there are double breakers that are 1/2 width. Those breakers only connect to one bus bar so they are truly 120 VAC only connections (with respect to neutral). L1 and L1 (for example) connections:

    https://www.homedepot.com/p/Square-D-Homeline-2-20-Amp-Single-Pole-Tandem-Circuit-Breaker-HOMT2020CP/202353308

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • billybob9
    billybob9 Registered Users Posts: 141 ✭✭
    #3
    Where does L1 to L2 happen at ? That would be 120vdc added to 120vdc to make 240vdc ? Would this be done in the transformer. That 30A two pole breaker that you show is what I am using as per SMA users manual so all is correct.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,693 admin
    #4
    Yes, the pole mounted (or other location) transformer feeding the L1/L2/N drop to your home is just a Center Tapped transformer (the center tap is the Neutral lead). And the Neutral lead is tied to ground (cold water pipe, ground rod, etc.):


    Just like taking two D Cell batteries end to end in series. Call the center connection between the two batteries Neutral.. V1 to N = +1.5 volts; N to V2 = -1.5 volts; V1 to V2 = 3.0 volts.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,693 admin
    #6
    My pleasure BillyBob.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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