Ground and Neutral connection for Split-Phase Switch Device

[再生可能 エネルギー]

I would like to build a Switch Device to connect a 240V load to either:
- the Grid or
- a Split-Phase Inverter (which is not Grid connected).

I plan to use a separate 2 poles relay to connect the load to one of the power input.
This part is straight forward, but regarding the Neutral and the Ground connection,
since my Split-Phase Inverter is not connected to the Grid, I think that some isolation relays
should also be used, but I could not find this information anymore, so I have few questions:

- About the Neutral wire:

1. Should the Neutral of the Grid, the Neutral of the Inverter, and the Neutral of the Load be connected all together all the time, or
2. Should the Neutral of the Load be connected either to the Neutral of the Grid or to the Neutral of the Inverter using a relay?

- About the Ground wire:

3. Should the Ground of the Grid, the Ground of the Inverter, and the Ground of the Load be connected all together all the time, or
4. Should the Ground of the Load be connected either to the Neutral of the Grid or to the Neutral of the Inverter using a relay?

So what would be your recommendation?

 

[FilterGuy]

- About the Ground wire:

3. Should the Ground of the Grid, the Ground of the Inverter, and the Ground of the Load be connected all together all the time, or
4. Should the Ground of the Load be connected either to the Neutral of the Grid or to the Neutral of the Inverter using a relay?

The ground is the easy part. All the devices should be tied to the same grounding circuit. No relays. No switches.

- About the Neutral wire:

1. Should the Neutral of the Grid, the Neutral of the Inverter, and the Neutral of the Load be connected all together all the time, or
2. Should the Neutral of the Load be connected either to the Neutral of the Grid or to the Neutral of the Inverter using a relay?

This is a little harder to answer because it depends on the inverter and how it is wired. What inverter are you going to use?

 

[再生可能 エネルギー]

The ground is the easy part. All the devices should be tied to the same grounding circuit. No relays. No switches.

Thank you, I put it because there are a lot of discussions on how to earth / ground an Off-Grid Inverter.

So maybe I didn't correctly write my question, but I guess the grounding issue
is when none of the output lines has a reference to the ground, such as using a resistance.

This is a little harder to answer because it depends on the inverter and how it is wired. What inverter are you going to use?

I am not decided about which inverter I will use yet, but it will be a stand alone Split-Phase Inverter, not an All-In-One system.
And it could be a combined unit, or two separate units where the two hot legs are combined into a 240 volts AC system.

I am considering for example getting a: Sigineer HP15048D

 

[hwy17]

Should the Neutral of the Grid, the Neutral of the Inverter, and the Neutral of the Load be connected all together all the time

With an unbonded inverter like a Schneider this is how you do it.

If the inverter is bonded you should see if you can unbond it.

Having inverter tied to building ground and neutral all the time is the best option, but it must be unbonded.

 

[FilterGuy]

I can not tell if the Sigineer HP15048D generates a neutral-ground bond.
However, if there is only one of the inverters:

• the grid neutral ties to the inverter AC-in neutral
• inverter AC out neutral ties to the load neutral.

This is true regardless if it is a common neutral with no bonding or a switched neutral with dynamic bonding.

However, there are a couple of things to watch out for:

1. Some split-phase inverters are really two inverters in one package. If both halves do dynamic bonding it creates two NG bonds. If possible, one should be disabled. However, since both are inside the unit, any undesirable current on the ground will be contained within the unit and should not be a big deal.
2. if there is a bypass switch to isolate the inverter and the unit is switched neutral with dynamic bonding, the neutral and both hots should be switched by the bypass switch.
   

 

[再生可能 エネルギー]

Thank you for the very precise answer.

I can not tell if the Sigineer HP15048D generates a neutral-ground bond.

From Sigineer website, I found some User Manuals with quite explanatory information, but I will reviews them separately.

However, if there is only one of the inverters:

• the grid neutral ties to the inverter AC-in neutral

In my case, for an Off-Grid installation, I don't plan to use any input, except to use the battery charging capability of the Inverter.
Some inverters also don't recommend connecting the Neutral to the Inverter Input (this is the case with the Sigineer Split-Phase)

With an unbonded inverter like a Schneider this is how you do it.

If the inverter is bonded you should see if you can unbond it.

Having inverter tied to building ground and neutral all the time is the best option, but it must be unbonded.

This the way I designed my Transfer Switch, expecting that the Inverter will have a Floating Neutral.
Especially also because I plan to have two Inverters (one single phase low power, and a split phase high power).

• inverter AC out neutral ties to the load neutral.

This is true regardless if it is a common neutral with no bonding or a switched neutral with dynamic bonding.

However, there are a couple of things to watch out for:

1. Some split-phase inverters are really two inverters in one package. If both halves do dynamic bonding it creates two NG bonds. If possible, one should be disabled. However, since both are inside the unit, any undesirable current on the ground will be contained within the unit and should not be a big deal.
2. if there is a bypass switch to isolate the inverter and the unit is switched neutral with dynamic bonding, the neutral and both hots should be switched by the bypass switch.

Thank you for clarifying this point regarding Dynamic Bounding, which was something no clear to me.