Dealing with Neutral output on SGP 6kW split phase connected to transfer switch

[plutoz]

I have the Sungoldpower 6kW non-solar inverter I purchased as a temporary solution to use a 48V LifePo4 battery in place of a backup generator until I am ready to upgrade to a real AIO inverter with solar in a year or so (probably will go with SolArk at that time).

I have an existing 2 pole manual transfer switch (which does not switch neutral) which was installed along with a L14-30 generator inlet on the outside of my house to be used with a floating neutral propane/gas generator. The transfer switch feeds a critical circuits subpanel. What I'm hoping to do is rewire so the inverter feeds the 'generator' side of the transfer switch, and then redirect the generator inlet to the input of the inverter so I can recharge the battery from the generator when it gets low. I will have to manually fire up the inverter and throw the transfer switch but that's fine.

I'm a bit confused about what to do with the neutral wire both from the generator and on the output side of the inverter. If you are familiar with this model of inverter you may know that it has no connector for the neutral on the input side (the wiring diagram in the manual simply says this wire is not required). It also comes from the factory with a green jumper wire which bonds the neutral and ground on the output side. I've already disconnected this and verified with a tester that the neutral and ground are not bonded once it is removed. The Sungoldpower manual also specifically mentions you should "never connect input neutral to output neutral". Here is the example wiring diagram from the manual:



What I am wondering is:

A) What do I do with the neutral output of the inverter, do I tie it back to the shared neutral bus inside the transfer switch which already has the neutral from the main panel (where it is tied to ground)? Or do I just leave it not connected?

B) Since there is no neutral input on the inverter do I just not connect the neutral from the generator inlet to anything, or should it be tied to the transfer switch neutral bar as well?

C) And lastly is it possible to also wire up a 120V outlet split off from the generator inlet before it goes to the inverter? In which case would the neutral for this outlet be connected to the generator (which has a floating neutral), transfer switch, or inverter (or a combination of these)?

 

[timselectric]

A) What do I do with the neutral output of the inverter, do I tie it back to the shared neutral bus inside the transfer switch which already has the neutral from the main panel (where it is tied to ground)?

Yes

B) Since there is no neutral input on the inverter do I just not connect the neutral from the generator inlet to anything

Yes

C) And lastly is it possible to also wire up a 120V outlet split off from the generator inlet before it goes to the inverter?

Yes

In which case would the neutral for this outlet be connected to the generator

Yes
This outlet should be a GFCI. Because it won't have a ground.

 

[plutoz]

This outlet should be a GFCI. Because it won't have a ground.

What if I tied the ground wire for this outlet (and the generator) back to the transfer switch which in turn is grounded to the main panel? That is how it is now with the generator connected directly to the transfer switch...

 

[timselectric]

What if I tied the ground wire for this outlet (and the generator) back to the transfer switch which in turn is grounded to the main panel? That is how it is now with the generator connected directly to the transfer switch...

That would be a problem.
Because of the inverter (no neutral input).
And it saying not to connect input and output neutral together.
The two systems (generator and house) need to remain isolated. The inverter is the isolator, in this case.

 

[plutoz]

That would be a problem.
Because of the inverter (no neutral input).
And it saying not to connect input and output neutral together.
The two systems (generator and house) need to remain isolated. The inverter is the isolator, in this case.

I'm not sure I follow, my question was about the ground not the neutral. The neutral and ground are not bonded in either the inverter or the generator. What/where should I be connecting the inverter ground to if not to the transfer switch?

The generator is a WEN Inverter generator. I assumed I wouldn't need a ground rod connected to the generator if I was connecting to the house panel through the transfer switch as this would provide connection to ground back at my main panel; this was all installed as part of a new construction and I haven't used the generator during an outage yet.

Does having a link to the utility neutral or not have any impact on how faults are handled? Ie with the current setup the generator's floating neutral is linked to the main panel via transfer switch's neutral bar. If I don't have a connection from the inverter's neutral output and the transfer switch is this potentially going to cause an issue if there is a fault somewhere?

I just don't want to get into a situation where I'm sending current back to the grid via the utility neutral inadvertently, that would obviously be bad. Or maybe I'm completely misunderstanding how all of this works...

 

[timselectric]

I'm not sure I follow, my question was about the ground not the neutral.

The grounding system begins and is created by the N/G bond.

The generator is a WEN Inverter generator. I assumed I wouldn't need a ground rod connected to the generator if I was connecting to the house panel through the transfer switch as this would provide connection to ground back at my main panel; this was all installed as part of a new construction and I haven't used the generator during an outage yet.

Correct
It is connected to the existing grounding system. As it should be.

Does having a link to the utility neutral or not have any impact on how faults are handled?

No,
Not how faults are handled.

Ie with the current setup the generator's floating neutral is linked to the main panel via transfer switch's neutral bar.

It's not floating, because it's connected to the house system.

If I don't have a connection from the inverter's neutral output and the transfer switch is this potentially going to cause an issue if there is a fault somewhere?

Yes
The neutral provides the ability to utilize 120v for loads. And the fault current path through the N/G bond at the main panel.

I just don't want to get into a situation where I'm sending current back to the grid via the utility neutral inadvertently, that would obviously be bad. Or maybe I'm completely misunderstanding how all of this works...

Current can't flow through the neutral alone.
There must be a completed circuit for current to flow.

 

[plutoz]

Correct
It is connected to the existing grounding system. As it should be.

Right, so once I disconnect the generator from the existing system and am only using it as a power source / input for the inverter aren't I breaking that connection?

It makes sense to me that I wouldn't connect the generator's neutral to the inverter (which it lacks an input connector for anyway) but I still can't wrap my head around why I wouldn't want all the grounds tied together. Unless I misunderstood you somewhere?

 

[timselectric]

Right, so once I disconnect the generator from the existing system and am only using it as a power source / input for the inverter aren't I breaking that connection?

It makes sense to me that I wouldn't connect the generator's neutral to the inverter (which it lacks an input connector for anyway) but I still can't wrap my head around why I wouldn't want all the grounds tied together. Unless I misunderstood you somewhere?

Ground, yes.
Neutral, no.

 

[timselectric]

Right, so once I disconnect the generator from the existing system and am only using it as a power source / input for the inverter aren't I breaking that connection?

If you are using it to feed the inverter. It isn't disconnected from the existing system. (As far as neutral and ground goes)

 

[timselectric]

Ok
I think that I see where the confusion is.
The generator is not floating in your current setup.
But it will be floating in the new setup.
Because it will be floating. (The inverter forces this)
You must keep the systems separate from each other.
Ground is one system for all. But neutral must be separate. Between the input (generator) and the output (the rest of the system) of the inverter.

 

[plutoz]

OK so does this drawing look correct?

 

[timselectric]

OK so does this drawing look correct?

View attachment 177832

Yes
Assuming that you forgot the critical loads panel?