Inverter question

8n-bob8n-bob Solar Expert Posts: 35 ✭✭
Hi All:

Been very busy and have not been on the boards in a while.

I have a question on my 120 VAC inverter. I have a Zantrex Prowatt 2000 watt full wave inverter.

Here goes the question.

On a normal wall receptacle you have 120 Volts between Hot and Neutral and also 120 Volts between Hot and Ground. I understand that Neutral and ground are tied in the breaker box. On my Zantrex and some smaller modified sine wave inverters you have 120 volts between Hot and Neutral but 60 volts between Hot and ground and neutral and ground.

So if you send power from the inverter to a small breaker box and and out from there. There is still voltage between Neutral and Ground when the Breaker is thrown.

I came across this by chance when I was hooking up my permanent solar set up and grounding every thing. I just checked voltage between what I thought was hot on the inverter and ground and only got 60 volts.

Now I don't know what to do in the breaker box. If I tie Neutral to Ground bad things I guess would happen :confused:

I searched the boards and did not find anything but I may not have searched correctly.

Well Take Care
BobO.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,641 admin
    Re: Inverter question

    In North America, "we" tie the Neutral (white wire/wide blade) to safety ground (green wire/frame of vehicle, ground rod/cold water pipe) for our utility power.

    For many TSW (true or pure sine wave) inverters, their output may be "floating" (think a full isolated transformer output), or it may be tied to the frame of AC inverter from the factory. Yours sounds to be floating.

    For most loads, floating or ground bonded or floating output does not really matter. The AC loads don't care, and for smaller inverters (typically less than 2-3 kWatt), safety wise, it really does not matter if the neutral is ground bonded or not (there are a whole bunch of details about safety theory we can discuss--if you like).

    There are a few AC loads that "care" and need a ground bonded neutral. Those include some florescent tube fixtures (tubes may not reliably start/turn on), and spark type ignition systems for natural gas/propane appliances (the flame detect needs ground bonded neutral).

    However, for portable systems, ground bonding may not make sense (no ground rod, no metal cold water pipes, etc.). The fact you have ~60 VAC from neutral to ground or from hot to ground (note voltage will probably "float" and may vary from 0 to 120 VAC to ground--Just depends on leakage current in the AC power system) will not affect the operation of any of the AC loads. May cause a bit of an issue with a GFI outlet (false trip).

    If you have a MSW (modified sine/square wave) AC inverter--Most of them will "smoke" if you attempt to ground bond the AC Neutral output.

    In any case, before you ground bond a neutral for an off grid AC inverter--Make sure to read the manual. Almost all TSW inverters can be ground bonded--And some will already be ground bonded neutral inside. And almost all MSW inverters cannot have their AC neutral ground bonded without self destructing.

    If you have a GFI outlet--If you ground bond the Neutral--You have to do this in the "input" side of the GFI and not the output side--Otherwise your GFI will trip.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 8n-bob8n-bob Solar Expert Posts: 35 ✭✭
    Re: Inverter question

    OK That explains a lot. If I ground bond the Neutral and Ground then the potential between those two goes to "0" volts and between Hot and Ground will go to 120. Got Ya.

    I'll check with the MFG to make sure if I can internally bond the ground to neutral.

    One other question that pops up and I think I know the answer.

    Lets say it's OK to do the internal ground bond before the GFI receptacle. Is it ok to bond ground and neutral in the breaker panel then. I would guess it's OK and Will not trip the GFI.

    Thanks for your Reply Bill Much Appreciated.

    BobO.
  • BB.BB. Super Moderators, Administrators Posts: 32,641 admin
    Re: Inverter question

    Ground in main panel, GFI on branch outlets after main panel.

    If you have a GFI on the inverter output, ground bonding at the main panel will trip the GFI on the inverter.

    Or can trip the inverter GFI... depending.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 8n-bob8n-bob Solar Expert Posts: 35 ✭✭
    Re: Inverter question

    OK So I should just bond inside the inverter, since the output on the inverter is a GFI plug. Then just run from that receptacle to the small breaker panel that I have and leave the ground and neutral not bonded. Or I can get rid of the GFI on the out put of the inverter and just put a regular receptacle in it's place and bond in the breaker panel.

    Thanks Bill

    BobO.
  • BB.BB. Super Moderators, Administrators Posts: 32,641 admin
    Re: Inverter question

    Yes. Those are the options. Either will work.

    Some like hard wired inverters, some like a plug for simple genset/inverter swap.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 8n-bob8n-bob Solar Expert Posts: 35 ✭✭
    Re: Inverter question

    Thanks for you Help Bill
    :D

    Have a great day
    BobO.
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