Neutral connection wiring for offgrid inverter with sub panel

[fabieville]

Where do you run the neutral connection from that goes to the inverter output? Do you run the neutral from the main panel disconnect or do u take the connection from the sub panel? Does it matter where it comes from seeing that its the same neutral in the main box that ties back with the one in the sub panel?

I have an off grid set up with a Main panel, sub panel and a transfer switch. I have 2 hots coming from the grid, sub panel where all my loads are and from the inverter going to my transfer switch but in regards to the inverter neutral connection should i run the neutral from the main panel box or take the connection only from the sub panel?

The neutral and ground bar are tied in the main disconnect box.
Running it from the main panel disconnect would be a shorter run to the inverter than taking it from the sub panel so i would use far less wire.

[joestue]

it doesn't matter. the neutral is one conductor not broken, switched, or fused anywhere.

[dnix71]

If you are not using a portable inverter, then the dwelling and inverter should meet NEC for a normal home. The transfer switch is almost always at the main panel, not a sub. You need to explain that first.

To safely backfeed, your inverter must be wired like the house. In the US, gensets under 5kw usually have floating neutrals. That is to say both plug slots on the output outlet are hot, 60v and out of phase so if you connect both across a load it adds up to 120v. This is the safe way for portable gensets. Touching one wire won't kill you, you have to touch them both at the same time to complete a circuit. The shell of the genset is grounded to earth somewhere nearby, but does not have a connection to neutral except in case you are using a grounded appliance and it shorts out. The ground in this case carries the short to the earth and away from you. You cannot backfeed a house in the US with a floating neutral source like that because the neutral and ground are tied together at the panels and inside the outlets.

On the US grid (a normal home in suburbia) the pole outside runs one wire phase through a transformer to step it down. The transformer is center tapped and the center tap is the neutral. From one side of the transformer to the middle is 120v and the other side is also 120v. If you use both hot wires you get 240 split phase.

Local code determines where the copper spike in the earth ground(s) must be located. And those are never at a sub panel as far as I know.

I'm guessing the inverter won't run everything, that is why you are making the connection at a sub.

[joestue]

In the US, gensets under 5kw usually have floating neutrals. That is to say both plug slots on the output outlet are hot, 60v and out of phase so if you connect both across a load it adds up to 120v. This is the safe way for portable gensets. Touching one wire won't kill you, you have to touch them both at the same time to complete a circuit. The shell of the genset is grounded to earth somewhere nearby, but does not have a connection to neutral except in case you are using a grounded appliance and it shorts out. The ground in this case carries the short to the earth and away from you. You cannot backfeed a house in the US with a floating neutral source like that because the neutral and ground are tied together at the panels and inside the outlets.

if the neutral is floating, when you read 60 vac its just phantom voltage. (also most generators are 120/240, floating)

if you google this exact question, you'll find a post by someone with a honda inverter generator with 80 volts on the neutral and 30 volts on the hot.  its all arbitrary to capacitance and leakage.

the ground wire to the generator does nothing except provide a ground to the shell of the generator in the event of a fault in the generator.

[fabieville]

My setup is a 220v high frequency hybrid inverter with input and output connections. But I don't use the input port which takes in L1, L2 and grounds. Instead I feed the output to a step down transformer to produce 120v. Then I feed the transformer 120v output to the inverter side on the transfer switch and then I connect the L1 and neutral coming from the main panel disconnect to the grid side of the transfer switch and then I connect the sub panel L1 and neutral to the load side of the transfer switch. My sub have all my load breakers.

My main panel disconnect with just the breaker for the grid alone is located close to my solar setup .Therefore can I use the neutral from it to connect to the load neutral slot on the transfer switch???
Instead of running a 30feet neutral wire from the sub seeing that the neutral in the main panel disconnect is the same like in the sub.

​​​​​​​I am only using 1 phase 120v that's why i am only working with the L1 & N from the grid and the L1 and N coming from the step down transformer.
Please note that the neutral and grounds are tied only in the main panel disconnect. Which setup is the correct one and will the switching of the transfer switch to either solar or grid goes smoothly without any issues?
Please note the transfer switches only 2 legs at a time. Either L1 and L2 or L1 or N

[dnix71]

I would not connect the neutral from one source of power to another. If something goes wrong the neutral may have enough voltage on it to cause damage to both systems since you tied them together.

A proper transfer switch isolates both sources completely from each other. Your appliances see one system or the other, the grid or your solar setup. That is why the transfer switch is supposed to be at the main grid panel.

Do Not connect the neutrals so if your solar is struck by lightning it will not run backwards and up the pole or into the house. If lightning strikes the pole it won't jump up or over into your solar sub and array. If you can't run everything from solar then you need an isolation transformer from the grid to feed the solar backed up sub panel. If the grid goes down the isolation transformer output is switched to the solar output. The solar sub panel should be grounded far away from the grid panel ground. If either side is struck the strike won't come up out of the ground to the other side.

[joestue]

If lightning strikes one circuit of you house it will reach into all circuits by nature of the ground wire being 1/4 inch away from the neutral wire.

Isolating and switching your neutral is not any safer, and wont protect anything.

Even in the event of a 48v battery grounded at one end and accidentally connected to the neutral, the 14 or 12 gauge neutral is just going to burn up. The voltage on it wont reach past that particular circuit unless you live in a house where all the neutrals are connected together with other circuits...which can happen