[RE-wrenches] N-G bond for supply side connection Midnite Power

Wed Oct 29 09:27:26 PDT 2025

One consideration that I've found to be valuable is ensuring the parallel
comm cables(inverters and batteries) are equal length. This may even
potentially be a more important consideration than AC lines being equal
length.

On Wed, Oct 29, 2025, 9:19 AM jay via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> It  seems like the inverters are not actually communicating for them to be
> so far off from each other.
>
> jay
>
> On Oct 29, 2025, at 8:58 AM, Dave Tedeyan via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> Jay,
> It is a grid tied system, and I am seeing this behavior while the grid is
> present. I have not been able to take a closer look to see if this happens
> during a grid outage. I am not even sure there has been a long enough
> outage yet as these systems are fairly new.
>
> And to be clear, these systems are generally working as expected. Even
> though this strange circulating current seems to happen many days, each
> system has only thrown the CA-DC link overvoltage error once.
>
> Cheers,
> Dave
>
> On Wed, Oct 29, 2025 at 10:43 AM Jay via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> These issues described here is this for both on and off grid?
>>
>> Jay
>>
>> On Oct 29, 2025, at 7:41 AM, Dave Tedeyan via RE-wrenches <
>> re-wrenches at lists.re-wrenches.org> wrote:
>>
>> 
>> William this is really good information, thanks for sharing the technical
>> perspective.
>>
>> I have two sites with two of these inverters and both of them are
>> exhibiting very similar behavior. On Friday, I was out at the other one to
>> wrap up a few things. While I was out there I verified some of the things
>> that Midnite tech support suggested like making sure that the AC wires to
>> each inverter's grid in and cables are the same length and also from the
>> battery bus bar to each inverter are the same length. This was actually a
>> bit surprising to me, considering with lead acid it is more important to
>> have the battery cables from the bus bar to the batteries be the exact same
>> length and the cables to the inverters did not matter as much.
>>
>> Based on what we were talking about last week, I removed the N-G bond in
>> the disconnect for the solar, but I have not yet gone looking for other N-G
>> connections in the way that Jason suggested. I have not gotten a CA-DC link
>> overvoltage error, but I have still seen some of the symptoms. It is not as
>> bad as the other site, but what I notice on the monitoring is that in the
>> late afternoon/early evening one inverter shows an unreasonable amount of
>> solar (with power going into the grid and into the battery), while the
>> other inverter shows low solar (with a ton of power coming out of the
>> battery going to the load and the grid), and the battery SOC drops very
>> quickly down to the discharge end SOC (on grid) setting of 85%.
>> Jason and William, do you know whether any faulty wiring with N-G
>> connected in loads on the non-backed up side will affect the system the
>> same way? Or is it mostly just important to check for any neutrals
>> connected to ground on the backed up loads side?
>>
>> Jason, as to why a supply side connection - I was under the impression
>> that a Power Control System just effectively limits the amount of power
>> that can be sold to the grid. But on a standard 200A service, that limits
>> you to about 7.7kw of sell back. I would not want to limit the system that
>> much for a roughly 20kw system, even if more than the 7.7kw can go to
>> powering loads and battery charging. In the Midnite monitoring, it is
>> pretty easy to limit the grid sell back with the "maximum feed in grid
>> power" in the Power Control settings.
>>
>> Cheers,
>> Dave
>>
>> On Sun, Oct 26, 2025 at 8:51 AM William Bryce via RE-wrenches <
>> re-wrenches at lists.re-wrenches.org> wrote:
>>
>>> All
>>>
>>> Most modern all-in-one (AIO) inverters are designed around a non-isolated
>>> high-voltage DC bus. This design is what allows manufacturers to advertise
>>> higher output numbers — for example, “15–18 kW” — while the inverter may
>>> only deliver 12 kW during nighttime operation when PV isn’t contributing
>>> (it is also cheaper to build). Without the shared non-isolated DC link,
>>> these power-boosted daytime ratings wouldn’t be possible.
>>>
>>> A DC-bus overvoltage fault almost always points to one of two issues:
>>>
>>>    1.
>>>
>>>    Improper system design
>>>    2.
>>>
>>>    Wiring and installation mistakes
>>>
>>> Off-Grid Example
>>>
>>> A common DIY mistake is pairing a large solar array (because glass is
>>> cheap) with a relatively small battery (not as cheap).
>>> When the battery is full and a large load suddenly turns off, the excess
>>> energy has nowhere to go. The inverter throttles back, but the stored
>>> energy can still push the DC-bus voltage up rapidly. If the inverter didn’t
>>> protect itself, the capacitors would be at risk — so it shuts down with an
>>> overvoltage error. This is also common when using a large retrofitted AC
>>> coupled array.
>>> Grid-Tie Example
>>>
>>> In grid-connected systems, DC-bus overvoltage is typically caused by wiring
>>> mistakes, some common examples are:
>>>
>>> Multiple neutral-to-ground bonds
>>>
>>> Reversed hot/neutral at outlets
>>>
>>> A single inverter is usually more forgiving. However, stacked inverters must
>>> share phase, neutral, and grounding relationships precisely. Any mis-wiring
>>> can create circulating currents. That circulating energy is not
>>> accounted for in the inverter’s internal power calculations, so the DC-bus
>>> voltage rises unexpectedly — and the inverter shuts down for protection.
>>>
>>> A DC Link Overvoltage error is usually not an inverter defect — it’s a
>>> system design or system wiring problem 99% of the time. Ensuring proper
>>> neutral/ground bonding, correct polarity, adequate battery capacity, and
>>> proper commissioning is critical to reliable AIO operation.
>>>
>>> This behavior is not unique to the MN AIO — all AIO inverters using a
>>> non-isolated DC-bus topology share the same fundamental protection
>>> limitations.
>>>
>>> Inverters are getting more complex to deal with the new rules and
>>> utility requirements, this causes reliability issues as we move (or pushed)
>>> to full integration with the grid.  Because you know we all want the
>>> utility to have full control over our systems!
>>>
>>> On Sat, Oct 25, 2025 at 9:51 AM Jay via RE-wrenches <
>>> re-wrenches at lists.re-wrenches.org> wrote:
>>>
>>>> I had an issue with a EG4 inverter and tech support was an insistent
>>>> that there was multiple ground neutral bonds in the system. Fully off grid
>>>> system with no generator.
>>>> It wasn’t the issue but it seems like these inverters are sensitive to
>>>> it.
>>>>
>>>> Is the inverter internally bonded, not that I’m aware of or what I’ve
>>>> measured.
>>>> And so I can’t figure out what it’s measuring between N/G to have a
>>>> potential issue.
>>>>
>>>> Maybe someone can explain?
>>>>
>>>> Jay
>>>>
>>>>
>>>>
>>>> On Oct 24, 2025, at 6:49 PM, Dave Tedeyan via RE-wrenches <
>>>> re-wrenches at lists.re-wrenches.org> wrote:
>>>>
>>>> 
>>>> Thanks all for your thoughts here. It seems that the general consensus
>>>> so far is that the N-G should be bonded in the solar main disconnecting
>>>> means when doing a supply side connection (even if it is not technically a
>>>> separate service). When talking with Midnite Power, we made it very clear
>>>> that we were talking about a N-G bond in the inverter combiner / solar main
>>>> disconnect, and not the backed up loads panel. And being that NY is still
>>>> on 2017 code (only going to 2020 next year), with the ambiguity in the code
>>>> I am probably okay to undo the N-G connection in the main solar disconnect.
>>>>
>>>> In this case specifically, we are backing up only a small subset of
>>>> loads in the house. The reason for the two inverters is because there is
>>>> about 24kw of solar. There is also a manual transfer switch to normally be
>>>> able to power the loads off the inverters, but to be able to switch to
>>>> powering the loads off the main panel in case of service needed on the
>>>> inverters. The neutrals in this system are all connected together, and I am
>>>> not sure if that could cause issues. It is probably difficult to explain
>>>> all the details in words, so I am copying part of the three line diagram
>>>> here. The second picture is the conductor and conduit schedule.
>>>>
>>>> Tom, I get it that the error sounds like it is on the DC side based on
>>>> the words, but when I talked to Midnite about it they were pretty clear
>>>> about it being due to multiple N-G bonds and they did not mention that it
>>>> could have anything to do with the DC side.
>>>>
>>>> Jason, that is a good idea as well to check the loads that got moved
>>>> over to see if there are any other inadvertent N-G bonds on the premises.
>>>> This also similar to what Midnite suggested, which was to lift the N-G bond
>>>> in the main panel and then see if they are still bonded somewhere else. It
>>>> seems like it can be a slow process to track that down with power cut to
>>>> the house, but that might be what I have to try if removing the N-G bond in
>>>> the solar main disconnect does not help.
>>>>
>>>> So, my main questions to anyone who has an opinion here are two fold:
>>>> 1. Do you bond the N-G in general in the main solar disconnect for a
>>>> supply side connection?
>>>> 2. Specifically with the Midnite AIO inverters, has anyone else had
>>>> issues with this "CA-DC link Overvoltage error" due to having a second N-G
>>>> bond in the house? (one in the main service panel, and one in the solar
>>>> main disconnect if it is a supply side connection). Or have you seen this
>>>> error and found that it was caused by something else?
>>>>
>>>> Cheers,
>>>> Dave
>>>>
>>>>
>>>>
>>>> On Thu, Oct 23, 2025 at 5:25 PM Jason Szumlanski via RE-wrenches <
>>>> re-wrenches at lists.re-wrenches.org> wrote:
>>>>
>>>>> I agree. It is not a separate service. It is a "tap" of the existing
>>>>> service (I use that term loosely here). The additional service disconnect
>>>>> for the supply side interconnection should have L1, L2, and N
>>>>> connected ahead of the premises main disconnect with no EGC. There should
>>>>> be a N-G bonding jumper in the PV service disconnect. Then there should be
>>>>> no N-G bonds downstream of both the premises main disconnect and the PV
>>>>> service disconnect.
>>>>>
>>>>> Basically, it's the same as two main disconnects running from a meter
>>>>> enclosure. Each of the service disconnects has a N-G bond required.
>>>>>
>>>>> Some AHJs (the crazy ones) require an EGC between the enclosure where
>>>>> the supply side connection is made and the PV service disconnect. This
>>>>> creates a parallel fault path, and should not be allowed, in my humble
>>>>> opinion.
>>>>>
>>>>> Now it sounds like you might be doing a partial home backup. The issue
>>>>> there is that sometimes the loads or enclosures you moved over the backup
>>>>> load panel have inadvertent N-G bonds. Sometimes it's as simple as someone
>>>>> who got creative and used a ground as a neutral in a switch box. I say
>>>>> simple, but that can be hard to track down.
>>>>>
>>>>> When Midnite said to remove it from the inverter distribution panel,
>>>>> they were probably talking about the protected loads panel.
>>>>>
>>>>> I think more information is needed.
>>>>>
>>>>>
>>>>>
>>>>> Jason Szumlanski
>>>>> Principal Solar Designer | Florida Solar Design Group
>>>>> NABCEP Certified Solar Professional (PVIP)
>>>>> Florida State Certified Solar Contractor CVC56956
>>>>> Florida Certified Electrical Contractor EC13013208
>>>>>
>>>>>
>>>>> On Thu, Oct 23, 2025 at 11:03 AM Tyrone Houck via RE-wrenches <
>>>>> re-wrenches at lists.re-wrenches.org> wrote:
>>>>>
>>>>>> My interpretation, and the way it was explained to me by both Ryan
>>>>>> Mayfield and Kyle Bolger(several years ago at this point, popular opinion
>>>>>> may have changed since). Is that it is not a seperate service.
>>>>>>  It is however required to have a ground-neutral bond( though in my
>>>>>> opinion pointless and redundant as there is a bond in the enclosure where
>>>>>> the tap is made). If it gives you any issue, ensure as close to equal
>>>>>> potential to the grounding electrode as possible(and make sure your neutral
>>>>>> is appropriately sized). I personally don't see the point but it is an NEC
>>>>>> requirement
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Thu, Oct 23, 2025, 6:08 AM Dave Tedeyan via RE-wrenches <
>>>>>> re-wrenches at lists.re-wrenches.org> wrote:
>>>>>>
>>>>>>> Hi All,
>>>>>>>
>>>>>>> For years I have understood that when doing a supply side
>>>>>>> connection, you are supposed to bond the neutral to ground in the solar
>>>>>>> service disconnect. I have a Midnite AIO system with two inverters (set up
>>>>>>> as a supply side connection) that recently was getting a CA-DC link
>>>>>>> Overvoltage error. When talking to Midnite, their first response was to
>>>>>>> make sure that there was only one N-G bond in the whole system. When I
>>>>>>> mentioned that the solar is a separate service and thus there is a N-G bond
>>>>>>> in both the main panel and the inverter distribution panel, they said to
>>>>>>> remove it from the inverter distribution panel. I want to make the system
>>>>>>> work right, but I also am hesitant to do something against how I have
>>>>>>> understood the NEC to be for a long time. I am curious if you all have
>>>>>>> thoughts on this or run into a similar situation.
>>>>>>>
>>>>>>> Cheers,
>>>>>>> Dave
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>> [image: Logo] <https://www.sungineersolar.com/>
>>>>>>> Dave Tedeyan, P.E.
>>>>>>> Owner | Sungineer Solar
>>>>>>> p: he | him | his
>>>>>>> a: 1653 Slaterville Rd.
>>>>>>> <https://www.google.com/maps/search/1653+Slaterville+Rd.+%C2%A0+%7C%C2%A0Ithaca,+NY+14850?entry=gmail&source=g>
>>>>>>>
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>>>>>>> NY 14850
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>>>>>>> c: (607) 270-0370
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