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EDITED TITLE: Why not common Neutral? What is dangerous about it?

FilterGuy said:
You may be correct, but that still does not answer the original question: What is dangerous about using these in a common neutral situation if the bonding screws are removed?

Maybe I am just dense, but I still don't see why using these with common neutral and no bonding screws is dangerous. I have a suspicion that if we could actually have a conversation with the electrical engineers that designed the units, we would find that the inverter can be used with common neutral if the bonding screws are removed. However, between the engineer and the customer there are a LOT of people that don't understand this stuff (this includes the US-based support engineers at the company and at the distributors.). I know this is a problem because of the number of times I have talked to the US-based support engineers that are clueless about even the most basic aspects of the inverters let alone a subject as detailed as this one. The unfortunate result is that by the time it gets to the customer, the message is that it is dangerous.
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Absolutely nothing makes it dangerous.
As long as you remove the bonding screws.
Based on my 38 years of experience.
But, I'm just a guy on the internet. lol
 
timselectric said:
Close, but not exactly.
What makes it a separately derived system is if the common neutral is separated and broken during the transfer.
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OK. I stand corrected.... I should have worded it differently. The end result is the same. With an independently derived system, the neutral is switched and the system provides its own NG bond. In a non-independently derived system, neutral is not switched and a separate ng Bond is not provided.

The interesting thing is that the engineers must have had some sense of or they would not have designed in the bonding screw. The presence of the screws implies that the original designers of the unit expected it to be used as either an independently derived source or a non-independently derived source.
 
FilterGuy said:
The interesting thing is that the engineers must have had some sense of or they would not have designed in the bonding screw. The presence of the screws implies that the original designers of the unit expected it to be used as either an independently derived source or a non-independently derived source.
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It was designed this way. because, everywhere except for North America. It needs to create a new N/G bond, whenever it disconnects from the grids N/G bond.
 
FilterGuy said:
In fact, not doing bonding and using a common neutral takes the inverter out of the bonding game and lets the local rules do what is appropriate.
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But it adds support and warranty costs when someone does it wrong.

You could/should design an inverter to automatically adjust bonding, but some utility systems (I believe MEN by UK standards, but @crossy likely has a better handle on it) will use various forms of multi-point grounding upstream with GFCI/RSD on the utility main. These differences, which often vary within a country, and make it hard to re-use a design.
 
FilterGuy said:
No, the GFCI does not need an NG bond before it to detect the problem. However, the problem does have to be downstream of the GFCI.
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I thought it detects the current difference between the two conductors (neutral and phase) if there is an imbalance, that means there is a current flowing to ground, would that not require a neutral ground bond before the GCFI?
 
LeoThomson said:
I thought it detects the current difference between the two conductors (neutral and phase) if there is an imbalance, that means there is a current flowing to ground, would that not require a neutral ground bond before the GCFI?
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No
Any difference measured between the two conductors, will trip the GFCI. No matter what path it finds to take.
 
Zwy said:
Manufacturers that have common neutral don't have N-G bond at the inverter under inverter power (battery as you refer to above) from what I've seen such as Deye/Sun Synk
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The Sol-Ark manual has common neutral in all of the diagrams. The inverter will throw up an error if the neutral/ground are not connected together in off grid mode.
 
timselectric said:
No
Any difference measured between the two conductors, will trip the GFCI. No matter what path it finds to take.
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But there wouldn't be a difference if there wasn't an alternative path right? (Hence the requirement of a connection before and after the GCFI)
 
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LeoThomson said:
I don't think you understand what I am trying to say and I don't know how I can make it clearer.
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I do understand what you are saying.
But you don't have to create any alternate paths.
As long as all of the power travels only through the GFCI, you are safe. That's why a GFCI can be used on a two wire system. And it's all that is required.
 
Quattrohead said:
The Sol-Ark manual has common neutral in all of the diagrams. The inverter will throw up an error if the neutral/ground are not connected together in off grid mode.
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I assume the Sol-Ark doesn't have dynamic bonding. It relies on a common neutral to provide bonding. I'm not too familiar with Sol-Ark but is it load sharing capable with grid? If so, that is why Sol-Ark uses the common neutral.
 
timselectric said:
I do understand what you are saying.
But you don't have to create any alternate paths.
As long as all of the power travels only through the GFCI, you are safe. That's why a GFCI can be used on a two wire system. And it's all that is required.
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Let me try it again. For there to be an imbalance to be detected there has to be a alternative path in one of the conductors (regardless if it is phase or neutral) both before and after the GCFI.
 
LeoThomson said:
Let me try it again. For there to be an imbalance to be detected there has to be a alternative path in one of the conductors (regardless if it is phase or neutral) both before and after the GCFI.
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Correct
But you don't have to create a path.
If an alternative path finds its way into the circuit, the GFCI trips.
If no path is detected, you can use the power safely.
 
timselectric said:
Correct
But you don't have to create a path.
If an alternative path finds its way into the circuit, the GFCI trips.
If no path is detected, you can use the power safely.
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There is one bond that we create on purpose, the neutral-ground bond before the GCFI, the second bond to create a path (accidentally) is a short between neutral and ground or phase and ground. (This accidental bond could also happen before the GFCI)

What we are worried about is ground loops, where we have one wire (usually neutral) connected to ground in multiple places, or am I missing what the main concern is?
 
LeoThomson said:
There is one bond that we create on purpose, the neutral-ground bond before the GCFI, the second bond to create a path (accidentally) is a short between neutral and ground or phase and ground. (This accidental bond could also happen before the GFCI)

What we are worried about is ground loops, where we have one wire (usually neutral) connected to ground in multiple places, or am I missing what the main concern is?
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Those are two different situations/ conversations.
A GFCI is a stand alone personnel protection device.
 
timselectric said:
Those are two different situations/ conversations.
A GFCI is a stand alone personnel protection device.
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Correct.

But the problem we are trying to solve is ground loops, a GFCI detects those, but I don't know if it is possible to put something like that on the transformers and inverters. Maybe it doesn't even have to trip and just give an audible warning.

I noticed my multiplus trip (and reset) with what I think was static electricity. Which made me think that maybe something like that could be the "solution"
 
Ground loops are easy to avoid.
But yes, you could use a GFCI on any circuit.
Or even the entire feeder.
I have installed several 2500 amp commercial services that had GFCI protection on the main. To protect the entire building system.
 
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