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Should the neutral wire from an autotransformer be bonded to ground in the breaker box?

uzernaam

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I'm running a completely independent system with no AC IN on the Growatt SPF 5000 ES to power a shed near my house. I have a 2 gauge cable running to a ground rod outside. This cable is connected to a ground bus bar inside a breaker panel. This is the only ground rod or ground connection on the system. (The house mains AC ground is on a different rod and the DC system is not connected to it in any way.) I'm creating a neutral using an autotransformer which connects to the neutral bus bar in the panel. Should I bond the neutral to ground in the panel? I'm vague on the answer to this so I don't want to proceed until certain.
 
There can be ONLY ONE LOCATION where neutral and Ground are tied together.
If the panel is powered by the inverter only, then that neutral is tied to ground. If the panel has ANY OTHER FEEDER, IT CAN ONLY BE BONDED THERE.
 
I understand the 1 ground point requirement.

The question is - could bonding the neutral from an autotransformer to ground damage the inverter? I have read some that some inverter designs might not like it.
 
The Growatt SPF 5000 ES has 240VAC output, no Neutral.
You need to run a ground from the panel to the Growatt.
The system you describe is completely isolated from the grid.
You need to bond the neutral and the ground in the panel where the transformer connects.
The ground connection in the transformer is a safety ground only, it is not bonded internally to the transformer neutral.
 
I just want to be sure that the circuit topology of the inverter won't know or care that its output goes to a transformer with a ground-bonded neutral tap. I hate smoke and sparks and lost $$.
 

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As long as the OUTPUT of the auto transformer is bonded in the panel only, and the inverter is connected to the input correctly, there will not be any connection internally.
 
The ground serves two functions, dissipation of induced currents and safety if a conductor energizes the case of a piece of equipment.
It isn't connected in a complete circuit under normal circumstances.
 
As long as the OUTPUT of the auto transformer is bonded in the panel only, and the inverter is connected to the input correctly, there will not be any connection internally.

See, that's the thing. There is no "output" (or input) - just three lead wires on the transformer - L1, L2, and N. I landed them on the bus bars. Some are saying that they need to connect through a breaker, but if I break the hots the neutral becomes unstable and suddenly you could see 240V on a 120V circuit from load/phase imbalance. You never want to put two AC 120V loads in series on 240V, which is the situation you get if the transformer becomes disconnected by its "protection."

Right?
 
Ok, the transformer is just creating a neutral… if you shut off the hots, the neutral is at zero to ground.
 
Ok, I see an issue… you have the output of the inverter feeding a breaker, and that breaker also connected to the auto transformer…
I would want a separate breaker panel for the output of the inverter, feeding the autotransformer. As it looks now, the breaker is always hot. Only way to turn off the AT is turning off the inverter.
 
I just want to be sure that the circuit topology of the inverter won't know or care that its output goes to a transformer with a ground-bonded neutral tap. I hate smoke and sparks and lost $$.
What Autotransformer did you get? Are you happy with it? Any issues?
 
Ok, I see an issue… you have the output of the inverter feeding a breaker, and that breaker also connected to the auto transformer…
I would want a separate breaker panel for the output of the inverter, feeding the autotransformer. As it looks now, the breaker is always hot. Only way to turn off the AT is turning off the inverter.
The inverter is attached to a backfeed breaker from the inverter.
It only has continuity to the busses in the panel when the breaker is closed. It's acting as a main panel breaker.
So, in principle, the backfeed breaker is also controlling the transformer which is direct wired to the bus lugs, but I agree the transformer should be on its own supply breaker.
 
See, that's the thing. There is no "output" (or input) - just three lead wires on the transformer - L1, L2, and N. I landed them on the bus bars. Some are saying that they need to connect through a breaker, but if I break the hots the neutral becomes unstable and suddenly you could see 240V on a 120V circuit from load/phase imbalance. You never want to put two AC 120V loads in series on 240V, which is the situation you get if the transformer becomes disconnected by its "protection."

Right?
The neutral is the output, L1 and L2 are inputs.
If you run 25A of 120V load on one leg the power runs up L1 (or L2) and down the Neutral to the load.
Being AC, the flow is actually back and forth.
But it needs both L1 and L2 connected as inputs to provide the midpoint Neutral output.

If you hook up 12VAC to the transformer to L1 and N, L2 will meter at 120V from N and 240V from L1.
Transformers are simple devices.
 
a Drawing / sketch of the setup will help us all understand better. Won’t it be better to use an isolation transformer rather than an auto transformer ?
 
See, that's the thing. There is no "output" (or input) - just three lead wires on the transformer - L1, L2, and N. I landed them on the bus bars. Some are saying that they need to connect through a breaker, but if I break the hots the neutral becomes unstable and suddenly you could see 240V on a 120V circuit from load/phase imbalance. You never want to put two AC 120V loads in series on 240V, which is the situation you get if the transformer becomes disconnected by its "protection."

Right?
Ok... if you break the OUTPUT of the inverter... there is no hot to feed the transformer, therefore, there will be no unstable 120V or 240V on the circuits.
 
Poz does a great job explaining bonding, and the autotransformer.
The comments section even has a nice explanation of what is going on.
 
This video does not address bonding neutral to ground…


this wiring diagram shows the neural going to the neural bar and then to ground

1636425781794.png
 
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