Safe Grid Use of the 5000ES and transformer

[timselectric]

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.

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

 

[timselectric]

Exactly what I did and it works perfectly.

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

 

[JohnGalt1717]

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

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.

 

[JohnGalt1717]

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

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.

 

[timselectric]

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.

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.

 

[wilsonb100]

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.

 

[timselectric]

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.

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

 

[JohnGalt1717]

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.

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.

 

[Pendrak]

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.

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).

 

[JohnGalt1717]

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).

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.

 

[Pendrak]

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

Why? taking only L1 and L2 from grid is like use the L1 and L2 on the inverter, in others words there will be no unbalance.

 

[JohnGalt1717]

Why? taking only L1 and L2 from grid is like use the L1 and L2 on the inverter, in others words there will be no unbalance.

(Well there is if there is an unbalance on the 2 legs of 120V created by the auto-transformer, but that's literally why you have the auto-transformer, to balance that out. So as long as you have excess over max unbalance, it is designed to handle it, and if you don't, then you're going to blow up all of your 120V stuff if the breaker on it pops, which we knew. That's why you overside your auto-transformer and by virtue of how electricity works, you'll only experience loss of having a second one hooked up if it's actually in active use. Otherwise it's balanced and thus no electricity flowing through it.

 

[Pendrak]

(Well there is if there is an unbalance on the 2 legs of 120V created by the auto-transformer, but that's literally why you have the auto-transformer, to balance that out. So as long as you have excess over max unbalance, it is designed to handle it, and if you don't, then you're going to blow up all of your 120V stuff if the breaker on it pops, which we knew. That's why you overside your auto-transformer and by virtue of how electricity works, you'll only experience loss of having a second one hooked up if it's actually in active use. Otherwise it's balanced and thus no electricity flowing through it.

You don't need do that if you connect the inverter directly to the autotransformer, if the breaker pops it will cut the inverter and the autotransformer at the same time...

 

[JohnGalt1717]

You don't need do that if you connect the inverter directly to the autotransformer, if the breaker pops it will cut the inverter and the autotransformer at the same time...

Yup, that's for the new one and that also implies that you have one auto-transformer per inverter which I don't, because I have a max 5000W imbalance (measured with extensive testing) on the 120V yet I routinely use 27kW of power while charging our car and running our heat pump and the dryer on and the dishwasher and hot water running.
So I have 6 inverters with 6 strings of solar, and 2 auto-transformers, of which one of them virtually never has any amperage on it at all. (I've yet to ever drive more than 5.1kW of total 120V and that was just in testing, normally it's under 1.5kW)
If I was to do it again, I'd use EG4s or switch to one of the new 96V inverter/solar charge controllers that do native split phase, but I don't have that kind of money, so I've just made sure I have enough capacity at the cost of a slight power wastage in all circumstances.

 

[Pendrak]

Yup, that's for the new one and that also implies that you have one auto-transformer per inverter which I don't, because I have a max 5000W imbalance (measured with extensive testing) on the 120V yet I routinely use 27kW of power while charging our car and running our heat pump and the dryer on and the dishwasher and hot water running.
So I have 6 inverters with 6 strings of solar, and 2 auto-transformers, of which one of them virtually never has any amperage on it at all. (I've yet to ever drive more than 5.1kW of total 120V and that was just in testing, normally it's under 1.5kW)
If I was to do it again, I'd use EG4s or switch to one of the new 96V inverter/solar charge controllers that do native split phase, but I don't have that kind of money, so I've just made sure I have enough capacity at the cost of a slight power wastage in all circumstances.

The second autotransformer don't need to be connected in that way...

I have 2 autotransfomer by the way.

 

[timselectric]

The two of you are welcome to do whatever you choose in your own home.
But please don't recommend it to others.
People come here to learn how to do it properly and safely.

 

[JohnGalt1717]

The second autotransformer don't need to be connected in that way...

The first one is a new one. It's in series with the inverter. The second one is installed with a breaker in the panel and a neutral back to the neutral bus bar. Is there a better way?

 

[JohnGalt1717]

The two of you are welcome to do whatever you choose in your own home.
But please don't recommend it to others.
People come here to learn how to do it properly and safely.

You've yet to give a scientific answer as to why we're wrong. Please do enlighten us. As an electrical engineer (i.e. my knowledge comes from a full understanding of the physics, not just a US Code book and the wrote memorization of an electrician), I love to be educated whenever possible.
(PS: My install passed inspection by the local building enforcement and he was an electrician before code enforcement. I explained it and why and he looked at the UL sticker and agreed that was the correct and only safe way to do it and signed off.)

 

[Pendrak]

The two of you are welcome to do whatever you choose in your own home.
But please don't recommend it to others.
People come here to learn how to do it properly and safely.

That diagram is from growatt not from me, that's the safe way to connect it.

 

[Pendrak]

The first one is a new one. It's in series with the inverter. The second one is installed with a breaker in the panel and a neutral back to the neutral bus bar. Is there a better way?

That's exactly the way i connect it.