ATS Grounding question

[FilterGuy]

I don't think that ATS just above is needed. Or the ATS IN would be connected to the generator. That inverter has an internal switch.

It is not really needed. However, some people like to put one in so they can bypass the inverter-charger for maintenance purposes. I get the sentiment.... but I don't think it is worth it.

 

[JASHOTZE]

It is not really needed. However, some people like to put one in so they can bypass the inverter-charger for maintenance purposes. I get the sentiment.... but I don't think it is worth it.

So I don’t have an inverter charger.

It is not really needed. However, some people like to put one in so they can bypass the inverter-charger for maintenance purposes. I get the sentiment.... but I don't think it is worth it.

so that diagram makes sense except the ATS has no earth ground out. Only L/N for inverter, shore power and output.

 

[FilterGuy]

So I don’t have an inverter charger.

so that diagram makes sense except the ATS has no earth ground out. Only L/N for inverter, shore power and output.

This would be the solution if the ATS has no grounding. Question: Is the ATS a plastic case or is it a metal case with a ground lug. If it has a ground lug, it would be like this:



BTW: Do you know if the ATS switches both line and neutral or just line?

 

[bruce_loco]

Let's separate the discussion. 1) How to string the ground wire between components

I will address the ground wire between components in this post.

Grounding.

If I am reading the OP correctly, the system has an inverter, ATS, and grounded DC negative. The way I would do this is shown below.

View attachment 71349
Inverters do not tie negative to ground internally, so there is no ground loop in the above diagram.

Inverter-chargers:

Some people like to install ATSs with inverter chargers so they can cut the inverter charger out of the loop for maintenance. Far too often, when an ATS is installed with an inverter charger, ground loops are unnecessarily created. In almost all cases the ATS and the Inverters will tie all ground inputs and outputs together. People dutifully connect everything together and end up with this:

View attachment 71347

In this case, the ground connection between the inverter output and the ATS is not needed. The following is properly grounded and does not have the ground loop.

View attachment 71348

Hi @FilterGuy do you see any problems with ground switching?
In the UK we have TNC-S, which means that the grounding is bonded with the neutral at the house entrance.
But if I am in full solar mode, if there is a ground fault, I would be be injecting the fault into the UK grid, hence the system is not fully off-grid.
I have a 3 pole contactor, and i thought to switch the ground as well, that way it is either fully off grid or fully on grid.
But sometimes you read stuff about "not switching the ground" which I can't understand why.

This is what I was planning:


Do you see any issues with this?

 

[FilterGuy]

Lets start with the basic question.

But sometimes you read stuff about "not switching the ground" which I can't understand why.

The ground wire is a fundamental part of the safety design of any system. As such, you want all connections in it and to it as solid and reliable as possible. Switching it creates a point of failure that is always(?) unnecessary in a stationary install. (I have never come across a need to switch neutral in a stationary install)

In the UK we have TNC-S, which means that the grounding is bonded with the neutral at the house entrance.

That is essentially the same as the US. The bond is at the service entrance, but on the customer side, not the utility side. The function is the same either way.

But if I am in full solar mode, if there is a ground fault, I would be be injecting the fault into the UK grid, hence the system is not fully off-grid.

What inverter are you using? Does it do dynamic bonding? If so, you probably are 'fully off grid" when in full battery mode.

 

[bruce_loco]

Lets start with the basic question.

The ground wire is a fundamental part of the safety design of any system. As such, you want all connections in it and to it as solid and reliable as possible. Switching it creates a point of failure that is always(?) unnecessary in a stationary install. (I have never come across a need to switch neutral in a stationary install)

That is essentially the same as the US. The bond is at the service entrance, but on the customer side, not the utility side. The function is the same either way.


What inverter are you using? Does it do dynamic bonding? If so, you probably are 'fully off grid" when in full battery mode.

Its the MPP PIP8048Max, the manual isn't really clear on grounding
All it has is:
"GROUNDING INSTRUCTIONS This inverter/ charger should be connected to a permanent grounded
wiring system. Be sure to comply with local requirements and regulation to install this inverter."

Which is fine, but adding the ATS adds complexity on the grounding

 

[FilterGuy]

Since you are in UK, it is probably a safe assumption it is a 230V version of the inverter. I do not have experience or information on the 230V versions, so I can only assume it does dynamic bonding. To verify this, please check for continuity between Neutral and ground when the inverter is disconnected from everything. If you find continuity, it is nearly certain the unit does dynamic bonding.

For the rest of this post, I will assume the inverter does dynamic bonding.

This is my best guess of the model of the dynamic bonding in the MAX:


Plugging that into your situation in the simplest arrangement we get this:


When in passthrough mode the inverter is sharing a ground but is otherwise completely isolated from the inverter
When in battery mode the inverter is sharing the ground but the output neutral and hot wires are completely isolated from the grid.

If you want to put an isolating transfer switch in, the story does not change.




Sharing ground does NOT mean a ground fault will be "injected" into the grid. The ground fault current on the output of the inverter will remain on the dynamic bond of the inverter.

 

[bruce_loco]

Since you are in UK, it is probably a safe assumption it is a 230V version of the inverter. I do not have experience or information on the 230V versions, so I can only assume it does dynamic bonding. To verify this, please check for continuity between Neutral and ground when the inverter is disconnected from everything. If you find continuity, it is nearly certain the unit does dynamic bonding.

For the rest of this post, I will assume the inverter does dynamic bonding.

This is my best guess of the model of the dynamic bonding in the MAX:
View attachment 132069

Plugging that into your situation in the simplest arrangement we get this:

View attachment 132070
When in passthrough mode the inverter is sharing a ground but is otherwise completely isolated from the inverter
When in battery mode the inverter is sharing the ground but the output neutral and hot wires are completely isolated from the grid.

If you want to put an isolating transfer switch in, the story does not change.

View attachment 132081


Sharing ground does NOT mean a ground fault will be "injected" into the grid. The ground fault current on the output of the inverter will remain on the dynamic bond of the inverter.

Yes, the UK is 230v.
I will do some continuity testing to check for the dynamic bonding. I asked MPP solar support as well just in case.
In conclusion I just need to the same ground for the whole system.

That makes it simpler.
Thanks

 

[bruce_loco]

Yes, the UK is 230v.
I will do some continuity testing to check for the dynamic bonding. I asked MPP solar support as well just in case.
In conclusion I just need to the same ground for the whole system.

That makes it simpler.
Thanks

Hi @FilterGuy

Response from MPP Solar for bonding on the MPP PIP8048Max:

When under line mode (AC bypass) = output N-G will remain open.
When under battery mode (solar or battery) = output N-G will bond

I will still check for continuity just in case :D

Thanks

 

[pablo131]

just to add for information. For my own MPP Unit, i got this reply from MPP
Hi Paul

By design the 2524GE does NOT come with a N-G ground screw, which means under battery/solar mode, output N-G will not bond and so it will behave per original design to be "floated". This is why you will measure a differential between N-G and this is perfectly normal. Reason N-G screw is not added on all the models is that some customers prefer dealing with N-G bond at the load distribution panel side by themselves, so in that case they will need to remove the screw.

Some models come with N-G screw by default, and when this happens:
1. LINE MODE -- N-G output will remain open, letting the AC mains panel decide (which should be closed anyway).
2. BATTERY MODE -- N-G output will bond (closed).

If you require the N-G bond feature, simply add a screw at the following location, marked in BLUE, on MAIN BOARD and this should resolve your problem.



P.S. Can anyone tell me the size of the screw? ta