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I am always surprised when researching online for a topic for a few hours does not bring solid responses. This is one of such situations.

I am in the process to provide AC power to a remote small garage on a budget, off-grid. I have access to decent quality used/reconditioned car batteries which will provide 12V and I will connect a rather unexpensive 1.2kW continuous (3kW peak) inverter with "modified sine" wave (not pure sine wave).

Where I cannot find a solid solution is on (1) grounding and (2) protection breakers.

I live in Italy where we have 230V 50Hz nominal AC power, single phase, for residential application.

  1. Grounding.
    I have read articles that recommend to ground one of the two AC output wires to simulate the grounding that is supposed to be done by power operators on the line before entering to the house. That would be my Neutral line. I would be supposed to tie to a ground rod one of the two AC wires (a specific one or any of them?) along with the Inverter housing and the negative terminal of the battery to create a common reference level. Another article however reports that on "modified sine" inverter, there MUST be a difference in voltage between Ground and Neutral wires, if not the Inverter will blow up. These note insist that there should not be any connection between Neutral and Ground and to use the inverter chassis as the Ground level only. This would leave Neutral floating.

  2. Protecting.
    I would like to have a reliable breaking box between the Inverter and the garage wiring. My understanding for what I read is to take the two wires out of the Inverter into a differential breaker type A 0.03A sensibility (not type AC nor type B) and then to Magnetotermic Breaker of 16A. Then the box will reach a ground rod on a separate third wire and from this box I will output the two 230V AC wires plus the Ground wire.

What's the right direction to proceed in principle and in practice? I would love some insight and pointer to proper solid literature on the topic.

Before you ask, the inverter documentation just refers to ground the housing to a metal ground of the vehicle (not my case) or the negative pole of the battery, but it says noting about the 230V AC, nor about Grounding to an Earth pole nor to how properly protect connected utilities with circuit breakers, maybe because intended application is to connect a single device, not a small garage...

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  • \$\begingroup\$ Is the inverter the only source of AC power for the garage? You said it is off-grid but I want to confirm. Also, please list make and model of inverter and link to installation manual if possible. \$\endgroup\$
    – mkeith
    Apr 27 at 21:38
  • \$\begingroup\$ @Mkeith : Confirmed totally off grid, inverter will be the only power source. The inverter i will try is this cheap linked below. Please don’t run in horror. I can’t provide manual details (yet). m.it.aliexpress.com/item/… \$\endgroup\$ Apr 27 at 22:27
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    \$\begingroup\$ Electric code may be different in Italy. But in the US, if an inverter is the only source of power, then either inside the inverter, or outside, neutral must be "bonded' to ground. There must be a connection from ground to a grounding electrode (metal pole buried in the earth). There are a lot of details. I assume it is customary in Italy also to bond one of the connectors to earth. This becomes the "neutral." After that, the electrical installation is very similar to any other electrical installation. You run the 3 AC wires (neutral, hot, and GND) into the electrical box.... \$\endgroup\$
    – mkeith
    Apr 28 at 0:09
  • \$\begingroup\$ and wire it just like any other building with breakers, etc. Personally I would buy a known brand inverter such as Victron or Siemens or something. I do not like no-brand low-cost inverters from China because I am afraid they will not work, or will be unsafe (start a fire). \$\endgroup\$
    – mkeith
    Apr 28 at 0:10
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If one of the inverter's output legs can't be grounded, I suggest getting an isolation transformer and run the inverter through that. Then, tie one of the transformer output legs to neutral, and also bond it to ground at your distribution panel where your breakers reside.

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  • \$\begingroup\$ Thank you, that is for sure a very clean solution. It is quite impacting for 1.5kVA - and I may then better consider upgrading to a more qualified inverter. \$\endgroup\$ Apr 28 at 18:10
  • \$\begingroup\$ Smaller inverters and generators assume portability, so they get away with driving both hot and neutral legs with voltage. Large ones are assumed to be fixed, and thus are designed to be integrated with building wiring, including a grounded neutral. So, yes, spending a bit more will address this. \$\endgroup\$ Apr 28 at 18:17

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