At home we have three 127v AC power supply, 120° from one another. I want to install grid tied PV array, and the project approved by the electrical company displays a single phase inverter connected to two out of the three phases available at home (I guess I'll have to choose the phase with higher load or something like that). The inverter in question is this one.

The problem is: nowhere in the manufacturer's manual such weird configuration seems advised. It is explicitly stated that it is a single phase device, and I must connect L, N and PE on the AC side of the inverter, which I take L to be the phase, N the neutral, an PE the ground (which is shorted to the neutral inside the electric box at home). I assume the project advises to connect ground to PE, phase 1 to L, phase 2 to N, and leave phase 3 out.

How is this supposed to work? Only one phase will be powered by the inverter and the other will be used simply as reference? Can it damage the equipment? Is such installation common?

  • 1
    You might want to say where "home" is, so that you get answers appropriate to your jurisdiction. However, I would say that if the project has utility approval -- depending on what that actually means -- you should be good to go.
    – Dave Tweed
    Mar 28 '18 at 18:58
  • It seems odd to me that your home is powered using three-phase power. It's certainly possible. It's just that I've never seen it in practice. Assuming you are correct about that (and I've no reason to doubt you), then I think you do have a problem here. Have you contacted those at the electrical company that approved the project itself and made sure they understood the situation you are asking here? The fact that you say "I assume the project advises..." suggests to me that the project doesn't actually advise anything. I think you could contact them and clarify these details, directly.
    – jonk
    Mar 28 '18 at 19:15
  • Disregard the fact that neutral is shorted to ground in one place. Neutral is not Ground. (except, obviously, inside the electric box at home). After that, location matters. Mar 28 '18 at 19:18

Looks fine to me. Consult with the manufacturer to assure the machine is internally built to be able to accept line wire on the "N" terminal. I expect it will be -- they couldn't sell any in North America/Colombia if not.

You have 3-phase "wye" power, Brazilian style. A single-phase load could either go corner-neutral (127V) or go corner-corner (220V).

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When you're backfeeding into the grid at a small scale, the same applies to feeds as loads. Since you can attach a single-phase 220V load to A-B, you can also attach a single-phase backfeed there.

It does not matter to which phases your house's loads are attached, because you know of course that a grid-tied solar inverter is totally incapable of creating power for your local use during power outages. That is not what grid-tied inverters do. If you want that ability, things get more complicated.

  • It may matter very little which phase I choose as load, but my reasoning is, if I choose the most loaded phase in my house, less power is carried back to the transformer at street, so at a global level we have a fewer losses. I don't know if it this is correct, and even if it is, it is probably a rounding error loss.
    – lvella
    Mar 28 '18 at 22:05
  • 1
    It would need to be a phase that loads while the sun is out. Air conditioning comes to mind. Yes, phase imbalance is annoying but the concept is, if everyone chooses random phases, it averages out. Mar 28 '18 at 22:22
  • Some places charge and net-meter on a per-phase basis, so if OP uses power on A phase and exports on B phase, they could be charged retail for the imported power but only paid a fraction of that for the exported power. Jan 1 '20 at 6:50

Reviewing the specifications and the schematic diagram on the bottom right of pg 1 of the Inverter spec., the output voltage of the inverter is going to be 220 VAC to 240 VAC (50 Hz or 60 Hz per your selection). The schematic has a 2 wire output and a chassis ground. One of the 2 output terminals is labeled "P" and one labeled "N". Service voltage at your home is 220/127V 3 phase, 4 wire, so phase-to-phase voltage is 220v which matches your inverter output. One "possible problem" that I cannot determine from the 2 page spec sheet is whether the output terminal labeled "N" is actually grounded internally which would prevent you from connecting the inverter to your service in its' current configuration. The Neutral of your service voltage is grounded and the 3 phase legs an not grounded, so you cannot connect a grounded inverter output to an un-grounded (but referenced) service voltage phase or you create a direct short circuit. If the Inverter circuitry does ground the "N" output terminal, it could probably be disconnected from its' internal ground (by removing a "jumper" inside the inverter).. I would not try that without consulting the manufacturer!
If the "N" terminal on the inverter is not bonded to the ground but is "floating", you could most likely connect the "N" terminal to one of the 3 service phase legs and the "P" terminal to a 2nd phase leg and the inverter would then supply 2 of 3 phases of your house distribution.
It is difficult to be more assured about advising you without knowing "everything" you "intended" or "believed" you would be able to power from your inverter once installed! I doubt you bought it thinking you would power the entire house, but probably power selected loads when the utility service failed. Provide more information and I will try and provide you a more specific answer.

  • Hello, and welcome to Stack Exchange. There's some great information here, but it's really hard to read without paragraph breaks (the "Wall of Text" effect). It would be great if you spent a minute or two making it easier to read. Mar 28 '18 at 23:21

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