Growatt 3000 SPF Floating Neutral (Solved for Now)

ChrisG

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A few of us here have been struggling what to do with ground/neutral on our Growatt inverters as there is much different behavior on ground/neutral when on UTIL power vs Solar/Battery power. My inverter will always be tied to main panel to charge batteries if no solar available where the only G/N bond occurs in my system. After searching and actual testing, I've found that when I jump the neutrals AC input and AC output on the growatt, everything works as expected. I have 0 amps on ground output and basically 0 volts between ground and neutral on output AND input running in either mode. I've tested this on a 12amp continuous load and below are the results. Prior to this I had up to 56v running on the ground wire when in Solar/Battery mode and a good amount of amps. Jumping the neutrals between input/output definitely solved the issue.

11/20/2021 Test Results:
Utility 12a Load: (the N/G 4.6v is something on this circuit within the house, nothing to do with inverter and I am looking into this separately)
  1. Amps on G: 0.01a
  2. N/G: 4.6v (measured same on input)
  3. L/G: 119v
  4. L/N: 115v
Battery 12a Load: (did not unplug GW, just changed to SBU)
  1. Amps on G: 0.02a
  2. N/G: 0.026v (measured same on input)
  3. L/G: 120v
  4. L/N: 120v

As I mentioned on previous tests while in Solar/Battery mode, there was a significant amount of voltage and current on the AC output ground wire which was caused me to rethink even using this product.

Big thanks to all those that helped guide me through many testing scenarios, especially @FilterGuy
 
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FilterGuy

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I have been trying to get a handle on how to properly set up the NG bond for Growatt for months. They previously supported using their dry-contact output and an external relay to dynamically generate the NG bond, but that is no longer supported in their latest firmware.

The solution that @ChrisG has worked out seems to work and is very simple, but I do not know if Growatt supports connecting the Neutral in and Neutral out. (I have an email to Growatt support asking them about this.)

Assuming Growatt does support connecting the neutral-in and neutral-out, then the following appears to be the best solution for stationary and mobile systems:
1637630395386.png
 
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Diysolar123

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in the ideal world you of course only want a single bonding...but then reality steps in ;-)
the best option is to put in a transfer switch that will handle the hot, neutral, and ground.
This means you will use your grid bonding when on grid power and when switching over the transfer switch contains the ground/neutral bonding and is disconnected from the grid connection entirely.

this is clean and straight forward...and a bit of a pain; basically you are bypassing using the inverter output when AC grid is available.

depending on wiring you have to consider two possibilities with input wiring and two responses by the inverter:
The two grid connection possibilities are wired or NOT wired...whether its a plug or hardwired, things can definitely get disconnected.
The inverter is either going to output the GRID power, or generate its own.
You cannot use a "normal" grid driven transfer switch (the relay coil is controlled by the presence of the AC in voltage) because even if the grid is up, the inverter CAN decide to switch to battery power!
So you must use a transfer switch that is controlled by the inverter.

(the following is NOT what you should do...however, to be honest I have my powerpack next to my grid input panel and I bonded the inverter neutral to a ground wire from the panel so regardless of the state of the input power wiring, the output neutral IS grounded)
The "second" bonding is a short run (6ft) and the output is a single isolated circuit, no GFI.; the proverbial "do as I say not as I do" comes to mind...)

always make sure that the ground is "grounded" and that the neutral is NOT floating...

1637638776213.png
 

ChrisG

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in the ideal world you of course only want a single bonding...but then reality steps in ;-)
the best option is to put in a transfer switch that will handle the hot, neutral, and ground.
This means you will use your grid bonding when on grid power and when switching over the transfer switch contains the ground/neutral bonding and is disconnected from the grid connection entirely.

this is clean and straight forward...and a bit of a pain; basically you are bypassing using the inverter output when AC grid is available.

depending on wiring you have to consider two possibilities with input wiring and two responses by the inverter:
The two grid connection possibilities are wired or NOT wired...whether its a plug or hardwired, things can definitely get disconnected.
The inverter is either going to output the GRID power, or generate its own.
You cannot use a "normal" grid driven transfer switch (the relay coil is controlled by the presence of the AC in voltage) because even if the grid is up, the inverter CAN decide to switch to battery power!
So you must use a transfer switch that is controlled by the inverter.

(the following is NOT what you should do...however, to be honest I have my powerpack next to my grid input panel and I bonded the inverter neutral to a ground wire from the panel so regardless of the state of the input power wiring, the output neutral IS grounded)
The "second" bonding is a short run (6ft) and the output is a single isolated circuit, no GFI.; the proverbial "do as I say not as I do" comes to mind...)

always make sure that the ground is "grounded" and that the neutral is NOT floating...

View attachment 73265
As best as I can tell by bonding the AC In/Out neutrals (ugly connection within Growatt limited space), it does not float the neutral on grid or solar/battery. Even when force tripping GFCI or Breaker or both. Not sure if there is a more definitive test I can do.
 

FilterGuy

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You cannot use a "normal" grid driven transfer switch (the relay coil is controlled by the presence of the AC in voltage) because even if the grid is up, the inverter CAN decide to switch to battery power!
So you must use a transfer switch that is controlled by the inverter.
That is mostly true. However, the ability to connect the input and output neutral presents an opportunity to manage it without the inverter involvement.

If the set-up is stationary, just connect the input and output and it will always see the single bond in the main breaker box.... problem solved.
(Yes, if things get disconnected, all bets are off.... but that is true with regular house wiring. If the bond gets disconnected it is a problem.)

For a mobile system, there are times when it is *expected* that the connection to the AC is lost, and the NG-Bond is lost with it.
That is where the relay I show above comes in. There are kinda 3 conditions:

1) Hooked up to shore power and shore power is turned on.
In this case, the relay turns on and hooks shore neutral to the system neutral. At that point, the system 'sees' the shore power NG-bond.. It does not matter if the inverter is in pass-through or inverter mode. Either way, the system sees the grid-provided bond.
2) Not hooked up to shore power.
In this case, the relay is off which means the system neutral is connected to the ground and that provides the NG-bond
3) Hooked up to shore power and shore power is turned off.
Presumably, this would be unusual, but it is a possibility so we have to consider it. In this case, the relay would be off so the Local NG-bond is created, but since the shore neutral is not hooked up, the system can not see the shore N-G bond. All is good.


The other thing that can get set-ups in trouble is the transition from one mode to another. If there are two NG-Bonds even for a moment it will pop an RCD/GFCI. With the circuit shown above, the neutral is disconnected before the local NG bond is created (and Visa Versa). This leaves a very brief moment where there is no NG Bond but there is never 2 NG bonds. (That is not ideal, but is common for these situations).

Even when force tripping GFCI or Breaker or both. Not sure if there is a more definitive test I can do.
Hmmm Tripping the GFCI is an interesting case for a stationary setup without the relay. I *thought* a GFCI disconnected both Hot and Neutral.
This would isolate the system from the NG-bond back at the breaker box. However, if you are not seeing the neutral float when the breaker trips, there must still be connectivity on the Neutral.
 

ChrisG

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Hmmm Tripping the GFCI is an interesting case for a stationary setup without the relay. I *thought* a GFCI disconnected both Hot and Neutral.
This would isolate the system from the NG-bond back at the breaker box.
Now I need to retest this after you mentioned that, I honestly can't recall. I'm thinking that might not be true as I said I'd always be hard wired (not GFCI). Will test again tomorrow and post back for those that will not be permanently connected to a grid or shore power where G/N are bonded at main panel.
 

FilterGuy

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Now I need to retest this after you mentioned that, I honestly can't recall. I'm thinking that might not be true as I said I'd always be hard wired (not GFCI). Will test again tomorrow and post back for those that will not be permanently connected to a grid or shore power where G/N are bonded at main panel.
If you find that a popped GFCI lets the system float, then the relay is needed any time there is a GFCI upstream from the inverter.

Keep us posted!!
 

FilterGuy

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In this video, if you look closely you can see that both Hot and Neutral are disconnected by a GFCI plug. Consequently, if the GFCI pops, it isolates the neutral from the circuit so there is no NG bond unless one in created locally. Consequently, the relay should be used for stationary systems that have a GFCI upstream from the inverter.

 

FilterGuy

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One more interesting point. A GFCI breaker in the breaker box does *not* disconnect neutral, so it would not have the issue.
 

tigerwillow1

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I realize the purpose of the video 2 posts up is to show which lines are disconnected, but just as a caution to anybody watching the whole thing, the description starting at 5:37 of how the sense transformers are used and how a ground fault is detected is close to 100% wrong. Contrary to what it says, the inner transformer senses current in both the hot and neutral, and the outer transformer is exclusively for neutral-ground bond detection. Additionally, the referenced chip is not an op amp used as a comparator, but rather an application specific GFCI chip. A different video correctly explains how the GFCI detection functions work. The use of outer transformer and grounded neutral detection starts at 3:35.
 

ChrisG

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@FilterGuy Retest complete. When I simply flip the breaker on the AC Input circuit, the load stays the same, on the neutral only. No volts or amps on ground like in my previous test which is good and this will be my hardwire scenario anyway. When I trip the GFCI on the same circuit, the neutral DOES float between Ground and Neutral, about 54v and minimal amps.

So I think the net is, if you hardwire your growatt into main panel (not plugged into outlet), bond the AC IN and OUT neutrals, you're good for all situations. If you plan on using your growatt plugged into a GFCI or in an RV shore power situation, you still need to deal with the floating neutral.

At this point I torture tested this Growatt 3000SPF. Max loads, wired up differently, duration tests, etc. Think I'm ready to commission it for use via hardwire to main service panel with a safe ground and neutral solution :).
 
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FilterGuy

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OK..... I just got a response from Growatt with good news:

Hi Paul,

We have two newer N-G version of SPF 3000TL LVM that came with Neutral and Ground interconnection and no need to do any extra wiring or setting. The customer can checks the nameplate to verify these specific N-G version.

Model Number was listed in the following
  • SPF 3000 TL LVM-24P – model# SKSL00.0010200
  • SPF 3000 TL LVM-48P – model# SKSL00.0010000

Other SPF 3000TL LVM-24P or -48P models without the setting 24 available, please connect manually the Neutral wire between inverter AC input and AC output like the diagram you provided in the previous email.

So..... my description above is correct for older models and they take care of it internally on newer models.
 

ChrisG

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@FilterGuy Awesome. Mine has Option 24, but I have absolutely no interest in the relay. Will just keep the neutrals bonded as I do now which seems to be supported by Growatt, which is even better news.
 

FilterGuy

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It has been a long and frustrating journey to pin down how to deal with Growatt grounding. The first problem was the lack of clear documentation from Growatt, the second problem was that their intended solution did not work with GFCI, the third problem was that their firmware was changing. It feels good to have a set of solutions that work and are supported. If growatt was not so popular here on the forum I would have given up long ago.

The next obstacle will be figuring out exactly what the new models do.... I suspect the new models will work just like the MPP models. The two brands seem to use the same firmware so my guess is the engineering is done by one company and the results are used by both. A long time ago, MPP had the external relay for bonding but they got rid of it. I suspect Growatt is just now catching up.
 

ChrisG

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It has been a long and frustrating journey to pin down how to deal with Growatt grounding. The first problem was the lack of clear documentation from Growatt, the second problem was that their intended solution did not work with GFCI, the third problem was that their firmware was changing. It feels good to have a set of solutions that work and are supported. If growatt was not so popular here on the forum I would have given up long ago.

The next obstacle will be figuring out exactly what the new models do.... I suspect the new models will work just like the MPP models. The two brands seem to use the same firmware so my guess is the engineering is done by one company and the results are used by both. A long time ago, MPP had the external relay for bonding but they got rid of it. I suspect Growatt is just now catching up.
@FilterGuy Do you happen to know the latest firmware for the SPF 3000 LVM 48v? I'm currently running 502.06/002.00. Looking at the Watts website I see this. Assume it's the latest. I've never tried a firmware update before so would be the first time.

1637805078566.png
 
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FilterGuy

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@FilterGuy Do you happen to know the latest firmware for the SPF 3000 LVM 48v? I'm currently running 502.06/002.00. Looking at the Watts website I see this. Assume it's the latest. I've never tried a firmware update before so would be the first time.

View attachment 73470
No. Sorry. I really don't know where to go get Growatt firmware/

Have a look at this post.


The link in there implies that there is at least a 510.xxx available.
 

ddanley

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OK..... I just got a response from Growatt with good news:



So..... my description above is correct for older models and they take care of it internally on newer models.

I really appreciate you folks tracking this down!

ChrisG states that "when I jump the neutrals AC input and AC output on the growatt," ... What does that mean exactly?

I have a plate/sticker on the side, but the model number is nowhere to be found. My SPF 3000TL LVM-24P is about a month old and I don't seem have option 24. Is there another plate hidden somewhere besides the one on the side?

Thanks again for the research on this!
 
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FilterGuy

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I really appreciate you folks tracking this down!

ChrisG states that "when I jump the neutrals AC input and AC output on the growatt," ... What does that mean exactly?
It simply means to hook a wire from the AC Neutral input to the AC Neutral output as shown here:
1637891150741.png

However, if there is a GFCI plug in between the inverter and the main panel, or if it is a mobile system, a bonding relay needs to be added as shown below:
1637891258578.png

I have a plate/sticker on the side, but the model number is nowhere to be found. My SPF 3000TL LVM-24P is about a month old and I don't seem have option 24. Is there another plate hidden somewhere besides the one on the side?
Could you please send a picture of the sticker you found?

Also, please look in the cable compartment for a nameplate/serial number sticker.
 

FilterGuy

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I really appreciate you folks tracking this down!

ChrisG states that "when I jump the neutrals AC input and AC output on the growatt," ... What does that mean exactly?

I have a plate/sticker on the side, but the model number is nowhere to be found. My SPF 3000TL LVM-24P is about a month old and I don't seem have option 24. Is there another plate hidden somewhere besides the one on the side?

Thanks again for the research on this!

BTW: I assume you have already looked at the back of the unit for the nameplate.
 
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