inverter to AC breaker box (off-grid)

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  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: inverter to AC breaker box (off-grid)
    bobdog wrote: »
    My question on using a single panel, was simply so I wouldn't have to have 2 panels. I figured your answer was the proper one (safe one!) and will just put in 2 panels. Down the road if i can afford one really nice TSW big boy, then I can do something else with the 2nd panel.

    Thought so.

    As for the two inverters into one panel...

    Can it be done?
    Sure. Just add a second isolated neutral bus bar and make sure to keep everything straight and separate. And, of course, do NOT tie the hot bus bars together - it MUST BE considered to be two separate systems living in one box.

    Should it be done?
    Not a chance - at least, not outside of an electronics lab. :)


    If you go the two panels route - then if/when you get an inverter big enough to feed everything, you can simply feed both panels from it.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: inverter to AC breaker box (off-grid)

    I am going to run the "K.I.S.S." flag up the poll and lets see how this works.

    We are talking about inverter(s) less than 600 watts, so do we really need a AC distribution center?? I can not see why, we need just one fuse/breaker for each inverter. If you use 14-2 wire or bigger, you really do not need either, why, the inverter can't supply current to damage the wire.

    Now, lets look at this item:
    http://www.amazon.com/Cooper-Bussmann-BP-SSU-Switch-Holder/dp/B001AQ2B96
    It is a fuse holder and switch in-one for a 2X4 box. Use one for each inverter. Now you have separate lines with a switch and fuse. For each box, Run a cord with male plug to one inverter and run the 14-2 romex for the cabin circuit(s).
  • bobdogbobdog Solar Expert Posts: 191 ✭✭
    Re: inverter to AC breaker box (off-grid)
    n3qik wrote: »
    I am going to run the "K.I.S.S." flag up the poll and lets see how this works.

    We are talking about inverter(s) less than 600 watts, so do we really need a AC distribution center?? I can not see why, we need just one fuse/breaker for each inverter. If you use 14-2 wire or bigger, you really do not need either, why, the inverter can't supply current to damage the wire.

    Now, lets look at this item:
    http://www.amazon.com/Cooper-Bussmann-BP-SSU-Switch-Holder/dp/B001AQ2B96
    It is a fuse holder and switch in-one for a 2X4 box. Use one for each inverter. Now you have separate lines with a switch and fuse. For each box, Run a cord with male plug to one inverter and run the 14-2 romex for the cabin circuit(s).

    Funny, I inherited one of those with the cabin. I like the idea. I would like to have many separate circuits for the cabin, but for now I can have a couple and be done with it. KISS, gotta love it.

    Why I think this may work for the time being is that I just decided to purchase (and did) a Morningstar 300watt SureSine inverter. From the limited reviews I've seen from this forum, it just made sense for now; dollar wise and quality. The point being that for now, I want to separate out the electronic gizmos, such as laptop, etc. from the lights (fan?) which can run off the cheapizoid MSW 750.

    I still think as my system may expand down the road I will put a panel in and get a larger inverter, but as of now I've achieved my initial goal of separation of circuits. I'll run the cabin with 2 circuits plus a DC or 2 for BU and go from there.

    Not knowing any better though, does anyone know if I can run the MS 300watt SureSine inverter with a 'real' neutral, or am I still in that '2-hot sides' mode?

    This thread has been one of the most helpful for me and I thank all those who helped along the way.

    Tim
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: inverter to AC breaker box (off-grid)
    bobdog wrote: »
    Not knowing any better though, does anyone know if I can run the MS 300watt SureSine inverter with a 'real' neutral, or am I still in that '2-hot sides' mode?

    In the manual, under "Step 3 - AC Wiring":

    "NOTE: The AC output is isolated, therefore AC line and neutral are interchangeable. Use UL Listed 12AWG (4 mm2) black wire for AC Line and UL Listed 12AWG (4 mm2) white wire for AC Neutral. The earth grounded leg defines AC Neutral."

    The illustration just above that shows neutral bonded to ground.

    Also:

    "4. Wire the white AC Line wire to earth ground. Check local code for appropriate earth grounding requirements."


    That doesn't exactly answer the first part of your question (and that's engineer territory so I don't have an answer either), but it does answer the second part; Yes, you should wire normally and bond neutral to ground.
  • bobdogbobdog Solar Expert Posts: 191 ✭✭
    Re: inverter to AC breaker box (off-grid)

    Thanks to all. Just got back from the cabin and the PSW Morningstar 300 watt inverter was waiting for me. I love Christmas in October!

    I will be going up to the cabin next weekend again and installing it. I can't wait. I can test it with the small amount of power needs I currently have.

    woo-hoo! new toys.....
  • System2System2 Posts: 6,290 admin
    Re: inverter to AC breaker box (off-grid)

    I am sorry to piggy back this thread, I was reading it and it somewhat pertains to what I am doing. The specifications of the inverter I am trying to connect is a 240vac inverter 7kw it has 3 terminal posts positive, negative, and earth ground. When i test the output of the inverter I get 240 across the positive and negative legs. When I test either leg to earth ground I get nothing. This tells me the inverter produces single phase 240vac not the two phase 120vac on each leg like I thought it did. I want to make sure before I transfer my house circuits over to the new breaker box that I have it connected right. On one main lug I connected the positive cable from inverter, on the other main lug I connected the negative. I connected the Earth Ground to the ground bar of new breaker box and connected that to the house grounding rod. Okay, I know the electric company sends two single phase 120vac legs to my house breaker box 180 degrees out of phase of each other. The inverter that I have doesn't have two phase capabilities; so what I did was connect one 15 amp circuit off each main lug and connected both common wires to ground making both circuits become series; but I tested this and burned out one of my test loads; one load got more voltage than the other which was rated at 115 volts and the other was rated at 117volts. The one rated at 115 burned out. What did I do wrong? I have a step down transformer 480/240 to 240/120; I tried to connect the 240 from the inverter to the primary but it goes into protect mode with no power output. I have to connect 240 on one half of the transformer's primary to get it to produce. Is there somthing I am missing. The primary has a center tap as well as the secondary I adjusted accordingly to the diagram as well as setting it for the desired output on secondary. Though when I tested this setup it worked but one side of the transformer overheated and shut down, I have not tested it since then and I am not sure if I burned out the transformer; hopefully I didn't. If i didn't burn it out, is it possible to reverse feed the transformer by putting 240 on the secondary and using primary as output? Instead of being step down will it be a step up? Currently I am not using the transformer. My thoughts are if I connect all circuits that I intend to the new breaker box that the voltage will stabilize and the earth gorund will neutralize any excess voltage. Is this correct? Thank you in advance.
  • BB.BB. Super Moderators, Administrators Posts: 29,497 admin
    Re: inverter to AC breaker box (off-grid)
    I am sorry to piggy back this thread, I was reading it and it somewhat pertains to what I am doing. The specifications of the inverter I am trying to connect is a 240vac inverter 7kw it has 3 terminal posts positive, negative, and earth ground. When i test the output of the inverter I get 240 across the positive and negative legs. When I test either leg to earth ground I get nothing.

    Just to be clear, there are +/- DC input power and LineA and LineB output (and a Neutral if it had one).

    Do you have a brand name/model number/website for this inverter?

    Details are important here... TYPICALLY, MSW (Modified Square/Sine Wave) inverters typically do not have isolated outputs. And you can smoke the inverter if you attempt to create a grounded neutral (and share the ground with the battery bank).

    And, again TYPICALLY, TSW (True Sine Wave) type inverters have transformer isolated AC output. The Transformer will either have two (LineA/LineB) outputs or three (LineA/Neutral/LineB) outputs. The Three wire "center tap" of the transformer is what is grounded/earth referenced for Split Phase 120/240 VAC inverters/utility-grid power systems.

    A pure two wire 240 VAC 60 Hz inverter is not real common... A pure two wire 230 VAC (European) inverter is standard for other parts of the world.
    This tells me the inverter produces single phase 240vac not the two phase 120vac on each leg like I thought it did. I want to make sure before I transfer my house circuits over to the new breaker box that I have it connected right.

    Is this a remote home with no Utility Power, or is this a utility connected home and you are looking for emergency backup power?

    If this is a utility powered home--You need to have an electrician install some sort of transfer switch setup. While you can make a DYI two input main panel by just flipping circuit breakers, it is not legal, and not really safe/accident proof (turn on both grid and inverter breakers at the same time).
    On one main lug I connected the positive cable from inverter, on the other main lug I connected the negative. I connected the Earth Ground to the ground bar of new breaker box and connected that to the house grounding rod. Okay, I know the electric company sends two single phase 120vac legs to my house breaker box 180 degrees out of phase of each other.

    Yep, think a three wire/center tapped transformer. The center tap (in north America) is tied to earth/safety ground. But has no other function in the 120/240 VAC wiring/power flow.
    The inverter that I have doesn't have two phase capabilities; so what I did was connect one 15 amp circuit off each main lug and connected both common wires to ground making both circuits become series; but I tested this and burned out one of my test loads; one load got more voltage than the other which was rated at 115 volts and the other was rated at 117volts. The one rated at 115 burned out. What did I do wrong?

    Without a center tap connection (pure 240 VAC two wire), you have just placed your two 120 VAC loads in series. If they are matched loads, they will each carry equal current and 1/2 the 240 VAC load.

    If they are unmatched loads, then one will carry nearly 240 VAC, and the other will see near 0 VAC.
    I have a step down transformer 480/240 to 240/120; I tried to connect the 240 from the inverter to the primary but the it goes into protect mode with no power output. I have to connect 240 on one half of the transformer's primary to get it to produce 120 on the secondary. Is there somthing I am missing. The primary has a center tap as well as the secondary I adjusted accordingly to the diagram as well as setting it for the desired output on secondary. though when I tested this setup it worked but once side of the transformer overheated and shut down, I have not tested it since then and I am not sure if I burned out the transformer; hopefully I didn't. If i didn't burn it out, is it possible to reverse feed the transformer by putting 240 on the secondary and using primary as output? Instead of being step down will it be a step up? Thank you in advance.

    There are lots of ways to "fix" the situation, and there are lots of ways to burn down your home and/or kill somebody.

    Do not do any "whole home" testing right now until you better understand the piece of gear that you have (manual, etc.). Inverters (MSW vs TSW vs Hybrid) and grounding/neutral/home wiring/shared neutral branch circuits--All serve to make the questions and answers fairly complex.

    If we do continue the discussion, I will copy these posts and put them in their own thread.

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