EDITED TITLE: Why not common Neutral? What is dangerous about it?
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timselectric
If I can do it, you can do it.
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The only one that I can think of would be stacked inverters in a completely off grid installation. (Bonding at first disconnecting means)
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Its funny, I did a google search on voltronics and the clones showed up.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Yes. The only configurations that work are ones that allow for a bond on the output of the inverter. If an un-bonded generator is hooked to the input it still works but If the grid is connected to the input it does not work.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
This why it is so alarming to me that they are now shipping with no bonding screws and are unwilling to say common neutral is supported.
In my email to EG4 I attached this document.
meetyg
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After reading this long thread, I have a question and would like to hear your thoughts:
My MUST inverter doesn't do any dynamic N-G bonding and doesn't have any bonding screws.
Our AC system is single phase, 220v European like (either TN-S or TN-C-S, not sure but don't think it matters for our discussion).
I will be using it both grid-connected and off-grid (like when powerco goes down).
I am considering common Neutral, but that means that I would have to take incoming Neutral BEFORE the main RCD in the main AC panel, because if the main RCD trips, it disconnects the grid Neutral.
Another option I was thinking of was to do dynamic bonding by programming a microcontroller (MCU) to communicate with the inverter's RS485 port and poll the inverter's working mode (technically its possible to do, I won't get into the details).
The MCU will be connected to a relay/contactor that will do the N-G bond, if it senses that the inverter is in off-grid mode.
The thing is, that it could take say a second or two untill the MCU senses this change and reacts, closing or opening the relay as needed.
This will cause either two N-G bonds for a few seconds (when switching back to on-grid mode) or have a floating Neutral (when switching to off-grid mode).
Do you guys see any problems with this ? I know that multiple N-G bonds are not good, but at worst it will only be for a second or two.
Also, how will some electronics react to the floating Neutral that will be grounded all of a sudden ?
I really don't understand why these manufacturers (including Growatt, MPP and MUST) have removed the option to control an external relay from thier firmwares, via the dry-contact on the inverters. I have seen some older manuals that state a menu option to choose what the dry-contact will function as: either as a generator start (when battery is low) OR to close/open an external bonding relay according to the working mode of the inverter.
But almost all newer models have this feature unavailable, and the dry-contact is used just for Gen start. Any thoughts why they did this major change?
It would have made our lives easier...
Could it be related to the response times as I mentioned with my proposed DIY solution?
Thanks...
My MUST inverter doesn't do any dynamic N-G bonding and doesn't have any bonding screws.
Our AC system is single phase, 220v European like (either TN-S or TN-C-S, not sure but don't think it matters for our discussion).
I will be using it both grid-connected and off-grid (like when powerco goes down).
I am considering common Neutral, but that means that I would have to take incoming Neutral BEFORE the main RCD in the main AC panel, because if the main RCD trips, it disconnects the grid Neutral.
Another option I was thinking of was to do dynamic bonding by programming a microcontroller (MCU) to communicate with the inverter's RS485 port and poll the inverter's working mode (technically its possible to do, I won't get into the details).
The MCU will be connected to a relay/contactor that will do the N-G bond, if it senses that the inverter is in off-grid mode.
The thing is, that it could take say a second or two untill the MCU senses this change and reacts, closing or opening the relay as needed.
This will cause either two N-G bonds for a few seconds (when switching back to on-grid mode) or have a floating Neutral (when switching to off-grid mode).
Do you guys see any problems with this ? I know that multiple N-G bonds are not good, but at worst it will only be for a second or two.
Also, how will some electronics react to the floating Neutral that will be grounded all of a sudden ?
I really don't understand why these manufacturers (including Growatt, MPP and MUST) have removed the option to control an external relay from thier firmwares, via the dry-contact on the inverters. I have seen some older manuals that state a menu option to choose what the dry-contact will function as: either as a generator start (when battery is low) OR to close/open an external bonding relay according to the working mode of the inverter.
But almost all newer models have this feature unavailable, and the dry-contact is used just for Gen start. Any thoughts why they did this major change?
It would have made our lives easier...
Could it be related to the response times as I mentioned with my proposed DIY solution?
Thanks...
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Many of the Voltronics clones used to not have the internal bonding relay, so they allowed dynamic bonding using an external relay via the dry contact output. As they added the internal bonding relay the removed the external control. When MPP made the transition, they released new firmware that took away the option of using the dry contacts and that hosed the people that had the old version.
I have never looked at Must inverters but I just downloaded a Must inverter manual.....and it sure looks like one of the Voltronics clones.
Interesting, I did not realize the RCDs in Europe disconnected neutral for some reason I thought they only disconnected the hot line. That certainly presents a problem. I'll have to read up on that.
If it is a Voltronic clone, you could probably do something like this:
If the RCD ever opened, the relay would disconnect the neutral from the grid and connect it to the Ground. There would be a moment while the relay is switching that it would be unbonded but I don't think that would be an issue for most things. Only a modern appliance that is actively checking for an N-G bond would be affected.
Notice that the above also assumes that the common neutral is acceptable. (It appears to work on other Voltronic clones)
Warning: The above is my guess. However, since I know so little about Must inverters, I can't say this is very definitive
meetyg
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Thanks for your suggestion!
So in your opinion it's best to have the inverter AC IN after the main RCD ? I was reluctant to have it before the RCD, for safety reasons. I do plan however to have an RCD on the inverter AC OUT (with DC current sensing too).
Would that now impose a new problem ?
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
If the RCD is breaking the neutral, there must be a good reason for it.... but I don't know off-hand what it is. However, Tapping the neutral before the RCD will thwart whatever the reason is.
None that I can think of.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
I sent EG4 support an email with details showing why shipping without the bonding screws makes things worse unless they support common-neutral. Their response indicated that they felt shipping without the bonding screws made the system NEC-compliant in most cases. Their answer did not mention common-neutral. I responded to that with a very direct question about support (or not) of common-neutral.
BTW: I also asked if they were shipping all of their inverters without screws.
I have not heard back, but the email was late enough on Friday that I would not expect an answer till next week.
BTW: I also asked if they were shipping all of their inverters without screws.
I have not heard back, but the email was late enough on Friday that I would not expect an answer till next week.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
My questions to EG4 support:
Their Response:
1) They refuse to answer a basic and critical safety question about what their product can do
2) They are making the situation worse on *all* of their inverters.
Unbelievable.
Zwy
Emperor Of Solar
Simply amazing they aren't clear on this. I currently have my EG4's mounted and wired, working on battery bank and will have to take the EG4 apart to see if a bonding screw is present or not as this was wired according to dynamic bonding being present in the unit.
Truly is unbelievable.
timselectric
If I can do it, you can do it.
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Not surprised at all.
12VoltInstalls
life passes by too quickly to not live in freedom
I am. Although some of what’s been discussed over this issue I understand at its basis I am not qualified to instruct or review the issue(s). Nevertheless, what it comes down to is a relatively simple design flaw as far as I can tell; that’s what surprises me. Because all that’s really required is discreet bare/ground and N, L(1,2) that is switched internally and automatically based on what the software sees regarding its installation environment.
That is only a slight step imho considering there are lesser expensive AIOs that actually do this now and have for a while.
So it boggles me that equipment which attempts to be competitive with top-shelf market segments cannot just incorporate the additional bit of hardware and program it accordingly. The issue is in the design phase in practice, but systemically is a R&D issue. I mean think about it: several lettered folks including Hedges picked this issue apart and out and - with no disrespect or negativity included - he can’t possibly be the most advanced or the only EE on the planet that could think this through, right?
Or am I too simple and naive to have said this?
timselectric
If I can do it, you can do it.
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Coming from the electrical installation industry.
The N/G bond required by NEC, is the responsibility of the installer. We provide it at the correct location, based on how and where the system is to be used.
I don't need or want an individual piece of equipment trying to be a one size fits all facilitator of the safety system that is my responsibility.
I always recommend removing the bonding screw from these AIO's. (When connected to the grid) because now, it's just a part of a larger system. And the newly combined system now has different requirements. Whenever you change an existing system. You should address it as a new system. And assess the requirements of this new system. Adding a piece of equipment to the end or beginning of a system is simple. But Adding it to the middle changes it completely.
The N/G bond required by NEC, is the responsibility of the installer. We provide it at the correct location, based on how and where the system is to be used.
I don't need or want an individual piece of equipment trying to be a one size fits all facilitator of the safety system that is my responsibility.
I always recommend removing the bonding screw from these AIO's. (When connected to the grid) because now, it's just a part of a larger system. And the newly combined system now has different requirements. Whenever you change an existing system. You should address it as a new system. And assess the requirements of this new system. Adding a piece of equipment to the end or beginning of a system is simple. But Adding it to the middle changes it completely.
Zwy
Emperor Of Solar
So how would you bond N-G with a pair or more EG4 6500EX's with screws removed that also has AC input? No common neutral either.
I'll be waiting for the response, and remember, it has to meet NEC to be "properly bonded" as PW says.
timselectric
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PreppenWolf
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I agree common neutral is preferred. I have not done this yet as I want guidance from SS first.
If they post a video saying multi-unit common is allowed I will be removing my bonding screws and going that route.
I would love to see an extra pair of N and G lugs added right next to each other under the bottom cover. Then get rid if the internal screw and provide a solid copper or stainless jumper instead. This would make it a lot easier to implement for DIY.
PreppenWolf
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Please note due to not having a common neutral for my current 2 unit 120/240 setup, I do see current on Ground from my offgrid panel to grid panel. I upsized the wire to handle full possible current in event of some issue. Obviously having current on ground is undesirable and an indication of loops.