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Safety hazard w/ Growatt 5000ES (European version) when connected to American grid

Do you tie ground of the inverter, transformer, breaker panel, and loads to ground of the utility meter and main breaker panel at service entrance?
All metal objects or those not double insulated are connected to the PE connection assuming such continuity survives the transfer switch
 
All metal objects or those not double insulated are connected to the PE connection assuming such continuity survives the transfer switch

Are you in the U.S.?
Compared to the schematic provided by Pendrak, Did you add a ground as shown?
If so, “Neutral” from utility is bonded to ground at the meter (in the U.S.),
And Neutral from split-phase auto-transformer is bonded to ground in panel as shown,
So some imbalance current flows in ground, either completing balancing of your loads, or attempting to balance utility grid.
“Objectionable Current.”

1667400494942.png
 
If you generate split phase from a relatively low power auto transformer and you unequally load the phases you will drag the neutral towards the higher loaded phase , this then create a higher voltage phase on the other split resulting in potegyoxk damage.

Referencing the neutral to earth ground “ anchors “ the neutral in this case the overloaded phase is pulled down but the other phase holds basically the same voltage as before.

There is a very serious deficit in this thread of first principle understanding and far too much obscure references to only slightly understood custom and practice techniques.
How do we avoid this?
 
Are you in the U.S.?
Compared to the schematic provided by Pendrak, Did you add a ground as shown?
If so, “Neutral” from utility is bonded to ground at the meter (in the U.S.),
And Neutral from split-phase auto-transformer is bonded to ground in panel as shown,
So some imbalance current flows in ground, either completing balancing of your loads, or attempting to balance utility grid.
“Objectionable Current.”

View attachment 118861
In general if a neutral PE bond exists at the grid entrance to the property , then no ground rod is needed. Hence this PE is the earth wire distributed to all cases and the centre tap of the auto transformer , the inverter DOES NOT have a ground bond to any phase wire.

The system is safe

However some transfer switches essentially kill the neutral pe bond. , is so then on transfer from the grid it may e neccessary to bring the ground rod into play.
 
In general if a neutral PE bond exists at the grid entrance to the property , then no ground rod is needed
So wrong, so horribly wrong.
What absolute crap you spew on this forum.
Who or what the hell are you ???

Look I will take a ban on this forum to point out what complete and utter shit so called technical advice you hand out on here. It is complete rubbish.
 
In general if a neutral PE bond exists at the grid entrance to the property , then no ground rod is needed. Hence this PE is the earth wire distributed to all cases and the centre tap of the auto transformer , the inverter DOES NOT have a ground bond to any phase wire.

The system is safe

Do you have this system, in the U.S.?
Can you provide a drawing of what you're talking about?
I used the drawing posted by another user.

Sounds like yours may or may not be different. But I think you said you have a ground wire from grid entrance of property over to the center tap of the transformer.
I believe that will result in some current flowing in the ground wire, which is considered improper. It is called "objectionable current" by some.

I am curious about a couple things:
1) What is the exact circuit you're using, including all ground rods, ground wires, and neutral wires. (so I can evaluate if there is a shock hazard or NEC violation.)
2) You've called yourself a "professional EE" a couple times. Do you hold a professional engineer's license, authorizing you to sign plans?
 
Do you have this system, in the U.S.?
Can you provide a drawing of what you're talking about?
I used the drawing posted by another user.

Sounds like yours may or may not be different. But I think you said you have a ground wire from grid entrance of property over to the center tap of the transformer.

Yes if the neutral earth bond is there.
I believe that will result in some current flowing in the ground wire, which is considered improper. It is called "objectionable current" by some.

No the current only returns in a vault condition.

Under normal load situations no current flows in the ground
I am curious about a couple things:
1) What is the exact circuit you're using, including all ground rods, ground wires, and neutral wires. (so I can evaluate if there is a shock hazard or NEC violation.)
2) You've called yourself a "professional EE" a couple times. Do you hold a professional engineer's license, authorizing you to sign plans?
I’m a member of the IEEE.
 
Yes if the neutral earth bond is there.


No the current only returns in a vault condition.

Under normal load situations no current flows in the ground

If utility transformer center tap (neutral) bonds to ground, and you route Ground, L1 and L2 but not Neutral to your inverter & auto transformer, and if auto transformer has center tap bonded to ground ...

Then yes, current flows in the ground wire. Because neutral created by each transformer is not exactly midpoint between L1 and L2, depends on loading on each phase.

Do you have a residual current meter? How much current is flowing in ground?
1667489556248.png
If you did feed your inverter and auto transformer with a 5 mA GFIC, it would probably trip.

I’m a member of the IEEE.

So no particular qualification to evaluate safety of utility grid connected circuits.
Just like a whole lot of us who have an EE degree from an ABET approved institution/program.
An "EE" who is "professional" in the sense he gets paid for it. But not a "license professional engineer" recognized as an authority by the state.

Not that "UL Listed" or "Signed by a PE" is either necessary or sufficient for something to be safe. But it is accepted as an authoritative indication.


If you do have a ground wire between utility entrance and chassis of inverter etc., that is much safer.
A vendor provided a schematic lacking that, for use in U.S., and I think that carried serious risks.
 
If utility transformer center tap (neutral) bonds to ground, and you route Ground, L1 and L2 but not Neutral to your inverter & auto transformer, and if auto transformer has center tap bonded to ground ...

Then yes, current flows in the ground wire. Because neutral created by each transformer is not exactly midpoint between L1 and L2, depends on loading on each phase.

Do you have a residual current meter? How much current is flowing in ground?
View attachment 119001
If you did feed your inverter and auto transformer with a 5 mA GFIC, it would probably trip.



So no particular qualification to evaluate safety of utility grid connected circuits.
Just like a whole lot of us who have an EE degree from an ABET approved institution/program.
An "EE" who is "professional" in the sense he gets paid for it. But not a "license professional engineer" recognized as an authority by the state.

Not that "UL Listed" or "Signed by a PE" is either necessary or sufficient for something to be safe. But it is accepted as an authoritative indication.


If you do have a ground wire between utility entrance and chassis of inverter etc., that is much safer.
A vendor provided a schematic lacking that, for use in U.S., and I think that carried serious risks.
You are clearly confused

A current returns to its source

The circuit is simple assuming PE and neutral bonded at the consumer grid input.

All metallic cases are bonded to pe. The neutral is bonded to PE at the auto transformer , the invertor has no live wire bonded

Split phase currents return to the auto transformer via the neutral. They do not outside of fault conditions return to the neutral via the PE.

This circuit is safe and to code.

Objectionable current is return current using case ground due to incorrect neutral Pe bonding. In essence the original problem was “ objectionable current “
 
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If utility transformer center tap (neutral) bonds to ground, and you route Ground, L1 and L2 but not Neutral to your inverter & auto transformer, and if auto transformer has center tap bonded to ground ...

Then yes, current flows in the ground wire. Because neutral created by each transformer is not exactly midpoint between L1 and L2, depends on loading on each phase.

The neutral of the auto transformer is bonded to PE. Other then case or pe fault currents no load currents flow in the bond

Your analysis is incorrect.
Do you have a residual current meter? How much current is flowing in ground?
View attachment 119001
If you did feed your inverter and auto transformer with a 5 mA GFIC, it would probably trip.



So no particular qualification to evaluate safety of utility grid connected circuits.
Just like a whole lot of us who have an EE degree from an ABET approved institution/program.
An "EE" who is "professional" in the sense he gets paid for it. But not a "license professional engineer" recognized as an authority by the state.

Not that "UL Listed" or "Signed by a PE" is either necessary or sufficient for something to be safe. But it is accepted as an authoritative indication.


If you do have a ground wire between utility entrance and chassis of inverter etc., that is much safer.
A vendor provided a schematic lacking that, for use in U.S., and I think that carried serious risks.
 
I'll bet my analysis is correct. In the case of power from utility passing through relays in inverter to auto-transformer, and loads.
If you post a schematic of what you're talking about, I'll double check and show what I came up with.

I've been going off schematics others posted, and your words. A representative schematic from you would be much better.

I don't know how much experience you have with transformers.
I'm something of a neophyte myself, although I've used them since childhood.
But what I have done is measure them to determine inductance, leakage inductance, loss, saturation current, hysteresis, inrush.
I've built SPICE models reflecting all those parameters, with some degree of success but not always a great match to reality.
For instance, I've produced relatively good models of a 3-phase choke, but a zig-zag transformer in simulation showed far lower neutral carrying current than expected.
 
Here’s the basic idea no ground rod needed if neutral PE grid bond is consistent across invertor transfer

Assuming 240 vac split phase

Personally I would fit 30mA RCBO the invertor input and output feeds.

screenshot 2022-11-04 103643.png
 
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I added Grid Neutral and explicitly showed PE bond.
I added a 120V load after auto-transformer.

When pass-thru relays of inverter are closed, either imbalanced voltage on grid or imbalanced load would result in on-trivial current in PE.
PE should only carry minor current like injected from parasitic or EMI filter capacitance, not return currents of load, which yours will (to the extent that auto-transformer has some winding resistance, so voltage droops under load.)
A You-tuber linked somewhere in the forum showed significant current in auto-transformer under no load, due to grid imbalance. That will occur with either neutral or PE connection to grid.

Residual current breaker would provide human safety protection in some situations, but would trip due to PE currents for your setup as shown.

1667574749657.png
 
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Go 6:50 mark, the drawing is just like what you propose.
Oh god does nobody read . Firstly the bond on the invertor must be removed

Secondly the contention the two transformers fight each other is nonsense because the neutral in bonded to ground a fact that video completely ignores.

These videos are seriously deluding people

Look here is Victron takes note the neutral bonding output of the auto traffo


41AD0446-E01C-4B10-9104-33DE05D36204.jpeg

The output relay neutral ground bond is a useful addition as no neutral bonding should exist when the invertor is not operating

The Victron diagram is the same as mine when the invertor is operating
 
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Here’s the basic idea no ground rod needed if neutral PE grid bond is consistent across invertor transfer

Assuming 240 vac split phase

Personally I would fit 30mA RCBO the invertor input and output feeds.

View attachment 119079

I ran an LTSpice model and did bench test of this.

Split-phase 120/240V input, but grounded Neutral not used, just ground connected to center-tap of auto-transformer (or not).
"Neutral" or "Ground" are same model in SPICE. Pretty much the same in physical implementation as well, except single phase loads in the property dump current into neutral.

For SPICE, I tried to define a reasonable 5kVA auto-transformer. It is modeled as coupled inductors with resistance.
With center tap ungrounded, all 7A peak was handled by the transformer. Ungrounded, current split about 50/50 between ground wire and centertap.

autotransformer_LTspice.jpg

For bench test, I used a transformer I had, good for a few amps, and Load was an oil-filled radiator.
Much wimpier than the transformer I modeled.
With center tap ungrounded, all 6.74A rms was handled by the transformer.
Center tap grounded, center tap carried 0.53A and ground carried 6.32A

Centertap ungrounded 6.74A IMG_3080.JPG

Centertap grounded 0.53A IMG_3081.JPG Ground 6.32A IMG_3084.JPG


You think your ground carries zero current?
Try measuring it.
 
Something in your spice model is wrong. Grounded neutral output on a transformer is extremely common. All U.K. building site 110 transformers are neutral earth grounded in essence these are 55v split phase systems.

Current returns to its source. Current will only flow through the ground line if the normal return is not available and then only under fault conditions.

I’m sorry but I used many auto transformers and under normal non fault conditions current does not flow in the PE wire. If it did all my RCBOs would trip.

If you really are concerned about this then a galvanically isolated split phase output put transformer can be easily sourced , ie 240 to 240 centre tap , this guarantees no current can possibly flow in the ground line, except under equipment failure conditions
 
I ran an LTSpice model and did bench test of this.

Split-phase 120/240V input, but grounded Neutral not used, just ground connected to center-tap of auto-transformer (or not).
"Neutral" or "Ground" are same model in SPICE. Pretty much the same in physical implementation as well, except single phase loads in the property dump current into neutral.

For SPICE, I tried to define a reasonable 5kVA auto-transformer. It is modeled as coupled inductors with resistance.
With center tap ungrounded, all 7A peak was handled by the transformer. Ungrounded, current split about 50/50 between ground wire and centertap.

View attachment 119393

For bench test, I used a transformer I had, good for a few amps, and Load was an oil-filled radiator.
Much wimpier than the transformer I modeled.
With center tap ungrounded, all 6.74A rms was handled by the transformer.
Center tap grounded, center tap carried 0.53A and ground carried 6.32A

View attachment 119394

View attachment 119395 View attachment 119396


You think your ground carries zero current?
Try measuring it.
Something is wrong here. Current returns to the source not via the neutral PE bond

We’re you using a auto transformer or sn isolating transformer.
 
Something in your spice model is wrong. Grounded neutral output on a transformer is extremely common. All U.K. building site 110 transformers are neutral earth grounded in essence these are 55v split phase systems.


Current returns to its source. Current will only flow through the ground line if the normal return is not available and then only under fault conditions.

Current will return to source but if a parallel path is provided, objectionable current will flow on a ground equal to 1/2 the total neutral current. It has nothing to do with "normal return is not available". If there is a parallel path, 1/2 the current will flow on each wire.

I’m sorry but I used many auto transformers and under normal non fault conditions current does not flow in the PE wire. If it did all my RCBOs would trip.

If you really are concerned about this then a galvanically isolated split phase output put transformer can be easily sourced , ie 240 to 240 centre tap , this guarantees no current can possibly flow in the ground line, except under equipment failure conditions
 
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