Safe Grid Use of the 5000ES and transformer

Relay disconnect of output (or input) when autotransformer disconnected should work. So long as it is just a transformer, without an over-temperature thermostat (don't think it has one.)

Is it the .pdf schematic in OP's post #1 you're referring to? I think others were posted somewhere in these 42 pages.

A simpler solution, but only supporting 120V total current up to transformer's capability not current imbalance to its capability, would be connect inverters to a 240V only loads panel, then use 25A dual breaker to feed autotransformer and 120V loads panel (no separate breaker for transformer, just tapped off main lugs). If breaker trips, autotransformer and 120V loads are disconnected.

However you do it, use wire gauge capable of carrying 50A for auto-transformer neutral. That's how much current will be in neutral if L1/L2 are each carrying 25A. Data sheet lists 42A (48A for 208V input) line to neutral current.

The data sheet I've found for one GroWatt transformer model appears to implement relay disconnect for lost neutral as you propose (different from what's in post #1), but details of internal wiring aren't sufficient to be sure:


"The rated power of secondary side L1-N and L2-N could up to 5kVA respectively, and the power difference between the two split phases can not exceed 1.5kW."

???

1.5kW / 120V = 12.5A
Are they saying that a single 120V, 1500W, 12.5A load on one phase and zero on the second phase is maximum it can handle?
Of course balanced loads, either 240V only load or identical sized 120V loads on two phases wouldn't involve the transformer.
But if 1.5kW is the most imbalance either 5000VA rated ATS 5000T-US or 11400VA rated ATS 11400T-US can handle, that is only 750VA actually going through the transformer core.

I suspect that someone who misunderstands transformers wrote that line, while the specs for amps per wire are correct.

Note that these two models, with quite different max power rating, have identical "Max continued current(L-N)".
That means they are the same transformer, but have different contactor. Victron similarly offers theirs with two different L1/L2 ratings but same autotransformer.

Oh, big difference with Victron's auto-transformers is that they switch neutral between grid connected and ground bonded. That makes it safe and compliant.
"UL Listed" or not, IMPO (in my professional opinion), no safe and effective configuration for use of Growatt ATS-US together with utility grid has been presented. Off-grid, seems fine.

Hedges said:

Oh, big difference with Victron's auto-transformers is that they switch neutral between grid connected and ground bonded. That makes it safe and compliant.
"UL Listed" or not, IMPO (in my professional opinion), no safe and effective configuration for use of Growatt ATS-US together with utility grid has been presented. Off-grid, seems fine.

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Only safe option is to use an isolation transformer, with the US version and grid pass through.
Which pretty much makes it less economical.

Trip.Diamond said:

This method of creating a 'separately derived system' is a completely acceptable way to go and should work best for most people!

It will require a separate grounding rod be placed not less than 8 feet from any existing ground rod. I would also use Shunt trip breakers for the output of the Growatts tied to the Transformer breaker. For added safety.

However I see a problem with the way you drew it in your schematic. You have a Ground line running from the Main Panel to the Sub Panel and then Bond it in the Sub Panel. This will create a Bond in two places as the Main Panel for Utility disconnect will already have a Neutral/Ground Bond in place.
View attachment 80282

If you remove the wire coming from the Main Ground you should be good.

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I have a similar system, and I got a schmatic from Signature, attached. A third breaker is located on the AC Out Panel. When connected to the utility, the AC out, from the GroWatt units, is connected to the utility, if you trace the wires. The path is fron the Inverters to the 3rd breaker, then to the Split Phase Transformer, then to single breaker in the load panel. And L1,L2 on the load Panel get utility power. Is this not a conflict, in that the inverters are not meant to be grid tied? What am I missing?

billduck said:

I have a similar system, and I got a schmatic from Signature, attached. A third breaker is located on the AC Out Panel. When connected to the utility, the AC out, from the GroWatt units, is connected to the utility, if you trace the wires. The path is fron the Inverters to the 3rd breaker, then to the Split Phase Transformer, then to single breaker in the load panel. And L1,L2 on the load Panel get utility power. Is this not a conflict, in that the inverters are not meant to be grid tied? What am I missing?

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Yup
Don't do that , with an autotransformer. (Only with an isolation transformer)
The N/G bonding in the loads panel is also a problem, when in grid mode. (There's no neutral from the grid) all neutral current will flow on the ground conductor.

Edit:don't do it with an isolation Transformer either.
It would still be back feeding.

mrzed001 said:

And here is the (possible) Online double conversion MPP Solar MK/MKX (alias Voltronic Axpert King and King 2) schema:

View attachment 82235


As you can see only the double conversion unit is doing always the AC/DC and DC/AC conversion.

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With the Axpert King II (which I've found in a Czech retailer), there's no way it should ever be feeding power into the grid, right? From the perspective of the utility company, it should be considered the same as an online UPS?

freedomlives said:

With the Axpert King II (which I've found in a Czech retailer), there's no way it should ever be feeding power into the grid, right? From the perspective of the utility company, it should be considered the same as an online UPS?

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Yes, it is exactly like an online (double conversion) UPS.
The only other solution is to buy a separate charger (AC/DC) and an inverter (DC/AC).

billduck said:

I have a similar system, and I got a schmatic from Signature, attached. A third breaker is located on the AC Out Panel. When connected to the utility, the AC out, from the GroWatt units, is connected to the utility, if you trace the wires. The path is fron the Inverters to the 3rd breaker, then to the Split Phase Transformer, then to single breaker in the load panel. And L1,L2 on the load Panel get utility power. Is this not a conflict, in that the inverters are not meant to be grid tied? What am I missing?

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Off Grid system with the GroWatt 5000es/us inverter I have 24 used 250 Candian Solar panels that are rated from 30.1 volts and 8.8 each. When I try to draw up a system to max the voltage and amps I have too many volts as the inverter says max volts is 450VDC but 100 amps. Any Ideas?

neuropa3 said:

Off Grid system with the GroWatt 5000es/us inverter I have 24 used 250 Candian Solar panels that are rated from 30.1 volts and 8.8 each. When I try to draw up a system to max the voltage and amps I have too many volts as the inverter says max volts is 450VDC but 100 amps. Any Ideas?

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I have the same inverter and panels. 10 in series is the max you can connect. Otherwise the DC bus voltage will get too high.

timselectric said:

I have the same inverter and panels. 10 in series is the max you can connect. Otherwise the DC bus voltage will get too high.

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This is my current production from 10s4p. (11am)

Thanks, I have all the pieces but have to build it, off grid in wyoming with a wind turbine as well

timselectric said:

This is my current production from 10s4p. (11am)View attachment 109540View attachment 109541

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Thanks, I have all the pieces but have to build it, off grid in wyoming with a wind turbine as well

If you are grid tie, why don't just use L1 and L2 from grid and use the autotransformers for neutral? in other words don't use the neutral that came from grid and let the autotransformers provide the Neutral when is in bypass mode and off-grid mode.

Pendrak said:

If you are grid tie, why don't just use L1 and L2 from grid and use the autotransformers for neutral? in other words don't use the neutral that came from grid and let the autotransformers provide the Neutral when is in bypass mode and off-grid mode.

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Exactly what I did and it works perfectly.

Same here.

Pendrak said:

If you are grid tie, why don't just use L1 and L2 from grid and use the autotransformers for neutral? in other words don't use the neutral that came from grid and let the autotransformers provide the Neutral when is in bypass mode and off-grid mode.

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That's a major issue for bypass mode.
All of the unbalanced load is going to be on the ground conductor.

JohnGalt1717 said:

Exactly what I did and it works perfectly.

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You just think it's working. Because your house hasn't burned down yet. And nobody has been electrocuted yet.
Luckily

timselectric said:

That's a major issue for bypass mode.
All of the unbalanced load is going to be on the ground conductor.

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No it won’t. (I’ve tested it). The unbalanced load runs through the auto transformer up to its cut off. That’s the entire point.

And it works exactly the same as the transformer on the pole: it’s just a center tap that derives neutral. So you have no more risk of unbalanced than the grid does and thus no more risk of shunting to ground than the grid. (Of course bonding ground is stupid in the first place but rewuired by code so they can cheat at the power company.

timselectric said:

You just think it's working. Because your house hasn't burned down yet. And nobody has been electrocuted yet.
Luckily

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I at no time have any power on ground. Anywhere. Doesn’t matter if I turn off everything else 120 and just run a microwave or not. An auto transformer is identical to the transformer on the pole except it has the same number of turns in as out and derives 120 of the center instead of also stepping down 11kV to 240.

JohnGalt1717 said:

I at no time have any power on ground. Anywhere. Doesn’t matter if I turn off everything else 120 and just run a microwave or not. An auto transformer is identical to the transformer on the pole except it has the same number of turns in as out and derives 120 of the center instead of also stepping down 11kV to 240.

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The autotransformer is being placed in parallel with the grid transformer. If you bond the neutral as required by code. You are creating a neutral path between the two transformers on the ground conductor. This is only a problem with an autotransformer, because it has no separation between the primary and secondary power. An isolation transformer has the separation to omit the issue.
Good luck and please don't miss any insurance payments.

OPPS Just checked again, and I have the grid neutral connected to the autotransformer.
I think that's why my house has not burned down ! Tim is always right.

wilsonb100 said:

OPPS Just checked again, and I have the grid neutral connected to the autotransformer.
I think that's why my house has not burned down ! Tim is always right.

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That's safer, but not perfect. (Unless you are the only house being served by the utility transformer)
And no, I'm not even close to mostly right. lol

timselectric said:

The autotransformer is being placed in parallel with the grid transformer. If you bond the neutral as required by code. You are creating a neutral path between the two transformers on the ground conductor. This is only a problem with an autotransformer, because it has no separation between the primary and secondary power. An isolation transformer has the separation to omit the issue.
Good luck and please don't miss any insurance payments.

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How so?
There is no ground to the transformer around here. The transformer has its own ground bar that is not connected to the house. There is only sweetbar from the transformer to the house. The neutral in the sweetbar is not connected anywhere. Only L1 and L2 and the ground is direct earth at the meter panel, the foundation and the wire connected to my well casing.

And all of the power, because of the ground bond, if there was any excess not handled by the auto-transformer (as long as the breaker doesn't pop) will shunt to ground, not the pole transformer. (or visa-versa) There's literally no path back to the transformer on the pole other than L1 and L2.

timselectric said:

The autotransformer is being placed in parallel with the grid transformer. If you bond the neutral as required by code. You are creating a neutral path between the two transformers on the ground conductor. This is only a problem with an autotransformer, because it has no separation between the primary and secondary power. An isolation transformer has the separation to omit the issue.
Good luck and please don't miss any insurance payments.

Click to expand...

I repeat myself, don't use the neutral from the grid, in others words go agains the code from USA (if this is really on the NEC code).

Pendrak said:

I repeat myself, don't use the neutral from the grid, in others words go agains the code from USA (if this is really on the NEC code).

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Exactly. Disconnect your grid neutral entirely and make sure there is no ground path back to the grid transformer. Then you're European 240V only on the grid and everything else is entirely done by the auto-transformer. That doesn't mean you shouldn't bond, everything expects bonding and will freak out if you don't have bonding somewhere. It just means that you're deriving your own neutral no different than using a transformer with a 1:1 winding and center taping it.
PS: This is exactly how shaver outlets in Europe work.