Auto Transformer Bonding

[Hedges]

Sounds like you could show them how to design a version which would support US as well as European market.
Demonstrated with cuts & jumps, now just needs to be put in the schematic and layout.

My Sunny Island provide info over RS-485 and programmable signaling relay for on/off grid. I may use that to switch an auto-transformer, for improved load sharing but not neutral-forming. So not as critical.

 

[automatikdonn]

I'm honestly not worried about the grid rebalancing issue. I haven't seen any of that actually happening in my other solaredge AT setup. I see it happening locally, but I have three different service entrances on this property. If I heavily unbalance the load on say service entrance 1 - I see no load on the ATs that are on service entrance 3.

At least not with the measurement tools I have here.

I have tested this using a walrus pump at different locations.

However proper bonding/grounding is a genuine concern.

 

[automatikdonn]

Main panel ground-grid neutral connect and auto transformer/aux panel ground-aux panel neutral connection means grid neutral is connected to aux panel neutral. The common connection between the two neutrals is done via the common ground wire.

This is due to the ground neutral bond in the main service entrance? I think I get the current flow now.

I was really hopeful that this setup would have just worked as is.

Something new to learn every day I guess.

 

[automatikdonn]

Geez I guess I missed the whole ES5K mega thread. I'm going to read back through that and maybe work up a wiring diagram that normal dummies like me can follow to safely and effectively use these units.

Thanks for all the response here guys. Your time is appreciated.

 

[Hedges]

Geez I guess I missed the whole ES5K mega thread. I'm going to read back through that and maybe work up a wiring diagram that normal dummies like me can follow to safely and effectively use these units.

I think that will be possible only for some configurations/applications.
Although, there are differing opinions on the forum.

Do post what you come up with and we'll see if we can find fault with it.

 

[automatikdonn]

I think that will be possible only for some configurations/applications.
Although, there are differing opinions on the forum.

Do post what you come up with and we'll see if we can find fault with it.

I think it's worth the effort to solve or at least semi solve for most use cases.

I would love if people can take their time to poke holes in it.

I will get back to this thread one I have something useful.

 

[Master Tinkerer]

I know we have all beat the brakes off this discussion - however please stick with me. It will be entertaining at the very least. Also mods if this thread is in the wrong place, please move it to the right place. I didn't really see a section of the forum that covers my question / line of discussion.

I have a LISTED auto transformer that is designed to be connected to the grid and then automatically switch over to off-grid / genset / etc when the grid goes down. Now this AT was designed with the explicit intent of being connected to the grid and was listed as such.

The question is about neutral bonding. Should I be bonding the neutral / should I not be bonding the neutral. I have asked around locally and nobody really can give me a non-circular answer.

Auto Transformers are covered in a couple places in the NEC.

210.9 Circuits Derived From Autotransformers
Branch circuits shall not be derived from autotransformers unless the circuit supplied has a grounded conductor that is electrically connected to a grounded conductor of the system supplying the autotransformer.

I read this as - if you have branch circuits coming off the AT - one must use a common ground.

215.11 Circuits Derived From Autotransformers
Feeders shall not be derived from autotransformers unless the system supplied has a grounded conductor that is electrically connected to a grounded conductor of the system supplying the autotransformer.

I read this as - if you need to use the output of an AT as a feeder - it must use a common ground.

So this brings me to my question - should that common ground be bonded in my split phase panel or not? See the image below.

View attachment 121422

Thank You!!!

 

[automatikdonn]

Here is the most simple version of this that meets the NEC sections I can find.

Feel free to poke holes in the design

 

[Sir Huff n Puff]

Hey There,

Total newbie to solar living in Panama here. I followed as much of your thread as I could regarding your setup and I think we're using similar things. I have on growatt 5000es inverter with 3 eg4 batteries running to a growatt ATS 11.4k. The system is currently operating as a grid-tied backup generator. I haven't set up solar yet. So far the system works when the grid goes down. It switches to batteries. I'm having an issue after the grid comes back. The system won't disengage fully and go back to grid bypass mode. The fans stay on and it registers an overload warning when using more than 5kw. I have to flip the breaker on the ATS (shutting house power off), switch the inverter to standby mode, then flip the ATS breaker on and switch the inverter back to on. Then it fully engages grid bypass mode. Any thoughts?

 

[automatikdonn]

Hey There,

Total newbie to solar living in Panama here. I followed as much of your thread as I could regarding your setup and I think we're using similar things. I have on growatt 5000es inverter with 3 eg4 batteries running to a growatt ATS 11.4k. The system is currently operating as a grid-tied backup generator. I haven't set up solar yet. So far the system works when the grid goes down. It switches to batteries. I'm having an issue after the grid comes back. The system won't disengage fully and go back to grid bypass mode. The fans stay on and it registers an overload warning when using more than 5kw. I have to flip the breaker on the ATS (shutting house power off), switch the inverter to standby mode, then flip the ATS breaker on and switch the inverter back to on. Then it fully engages grid bypass mode. Any thoughts?

I have no ideas why it would be doing that. I would check your settings to ensure that you are picking the correct modes. I will say that you may consider not running more than 5kw through that inverter in any mode. Are the terminals on the physical connections rated for more than 5kw?

 

[Sir Huff n Puff]

I have no ideas why it would be doing that. I would check your settings to ensure that you are picking the correct modes. I will say that you may consider not running more than 5kw through that inverter in any mode. Are the terminals on the physical connections rated for more than 5kw?

I believe so. When running in grid bypass mode the unit functions fine, even with loads higher than 5kw. No overload alerts. It's only after the grid goes off and comes back on that the issue arises. The display shows grid bypass but the fans are still on and it the use percentage acts like I am still on batteries. When I use a high load appliance (electric tankless, already planning to switch to gas), the unit, while showing grid bypass, goes into overload alert. It doesn't shut down, but the fans spin up and it acts like I am using more than 5kw, as if it thinks it is still running from battery.

 

[Hedges]

Is it drawing from the battery, or from grid?
Just look at your utility meter, if you don't have suitable DMM.

I expect fans to spin up due to temperature rather than measured current, but you never know.

 

[Sir Huff n Puff]

This happens after the inverter should be switching back from battery to grid. I am on the grid at this time, the batteries are not being used. however, the inverter is performing like it is using batteries, spinning up the fan when there is a larger draw. This is occurring when it is supposed to be in grid bypass mode. Does that make sense?

 

[Hedges]

That is what you describe, or think. But you haven't indicated you actually confirmed the power is in fact coming from grid.
Just that it ought be be, but inverter behavior seems inconsistent with that.

 

[Sir Huff n Puff]

Sorry I wasn't clear. I did check that by turning the batteries off. It is on grid. Shouldn't that be sufficient to check?

 

[Hedges]

Yes, with no solar that does confirm.

Seems to be a firmware issue, in that it has clearly closed the relay, yet is powering fans and implementing a current limit.
I was thinking for a moment battery charging consumed some of maximum allowed input current, but that couldn't be the case if batteries are shut off.

Maybe it would behave differently with some PV connected. Can you try that?
Manufacturer may not have tested how it behaves as a battery-only UPS. Although, that should be expected for grid failure and recovery at night.

 

[Sir Huff n Puff]

I, unfortunately, do not have solar yet. It's coming as soon as the $$ is right. We have a poor grid that goes down often, thus the backup generator aspect for now. I checked the firmware and it seems to be the latest: 040-05-7.01 top and 04-05-7.01 bottom. I also have the wifi stick installed and working. that should update firmware, no? Is there anything else I can do? I've reached out to Signature Solar already, waiting for a "tier 2" response team to advise. Returning to Signature Solar from Panama will be difficult and expensive at best.