Design Review - Growatt SPF 5000 ES Grid Backup & Neutral Bonding

[automatikdonn]

How does the 120V N load current decide which Transformer to use? Being that the Grid Transformer and the Auto Transformer are in parallel.

There is no neutral coming from the Main service entrance to the inverter, only two hot legs out of phase. One would think a 120V circuit will follow the path of least resistance and it would be derived from the Solar Load service panel in my drawing. Is that not how it works?

 

[LeRoyK]

Is the ground disconnected in Off Grid mode? I don't actually have these interters operational just yet, so I can't really check mine.

AC IN and AC Out Grounds are connected internally.

>+1 on needing a N/G bond in your 'solar load service panel' of post #37 @automatikdonn - right now it looks like your setup would not be able to clear a ground fault due to the lack of that N/G bond.

I am trying to understand the current flow and why that is. Is there anyway we can collaborate on a drawing so people can see all of the failure modes and protection mechanisms that can be put in place to handle those failures.

see the attached drawing of Ground Fault Example.

 

[Desert_AIP]

Stumbled on this video today, using the Seauto transformer with a SolArk.
The SolArk has a transformer inside to output split phase.
I think this would be a similar setup if running two Seauto transformers with a pair of the Growatts.
A pair of the Seautos would give you Neutral redundancy.

 

[LeRoyK]

There is no neutral coming from the Main service entrance to the inverter, only two hot legs out of phase. One would think a 120V circuit will follow the path of least resistance and it would be derived from the Solar Load service panel in my drawing. Is that not how it works?

See attached example of potential neutral current flow in ground wire if we add a second N/G Bond. In 'Solar Disconnect Service Panel' the Neutral current can go two different ways, #1 through N/G Bond back to Main Service Neutral or, #2 Through Auto Transformer to L2.
Sorry to make a mess out of your pretty drawing!



Here is How I suggest doing it. Connect ' Solar Disconnect Service Panel' Neutral to Main Service Panel Neutral, this will allow a ground fault to be cleared even when in Off-Grid Mode.

 

[??????]

@LeRoyK - I think the single main service panel N/G bond design is about as close as we can get. The only problem with this is that our AT is in parallel with the grid (pole) transformer so they're sharing the work of balancing the phases when we're in an on-grid scenario (L1/L2 connected through GW). That's effectively what Ben is doing In the video @Desert_AIP posted, and it seems to be working for him. Just cause it works doesn't mean it's code-correct though (I'm fairly sure this is a code violation, but not sure where in NEC it says it).

I think the only way to do this 'properly' is like this:

• On-grid: single G/N bond on the main service panel. L1/L2 of AT are disconnected from any subpanels. The grid/pole transformer is the only thing forming neutrals on any of our subpanels.
• Off-grid: add G/N bond conditonally (setting #24) on the subpanel. Connect L1/L2 of the AT to form the neutral. Grid transformer does not participate in neutral forming.

I believe this is how the Solaredge StorEdge solution (which was the original design use for the SE Autotransformer, see pg 31) switches this way. It has a 2s transfer time, which leads me to believe that it has internal controls to validate the neutral is formed with 120V on both legs prior to switching the internal ATS to the subpanel load. Doing things this way keeps the grid transformer and AT separated. The challenge here is validating neutral forming logic outside of a GW inverter since we're synchronizing a transfer across multiple external components with no comms bus/etc.

I'm pretty sure the design @automatikdonn and myself discussed can be extended to do this since the neutral forming validation is controlled by the 'OVER VLTG' protection relays, which performs the transfer in two stages (first GW internal, then externally with contactors)

 

[Desert_AIP]

LeRoyK is correct, I edited my posts.

I neglected to consider the path back via ground to the grid neutral when there is a second bonding point in the derived panel and drawing 120V power on the secondary panel.
I was in error. That would result in the ground acting as a current conductor, which is bad.

I still think you need a derived panel with the Growatt fed loads in it.
But I think you would configure it the same as any other grid tied sub panel.
Pulling 4 wires (L1, L2, N, G) from the main panel (L1 and L2 through the Growatt) and NOT bond N and G in the derived panel.

The Autotransformer is not internally bonded, the ground connection to it is a safety ground.

 

[LeRoyK]

@LeRoyK - I think the single main service panel N/G bond design is about as close as we can get. The only problem with this is that our AT is in parallel with the grid (pole) transformer so they're sharing the work of balancing the phases when we're in an on-grid scenario (L1/L2 connected through GW). That's effectively what Ben is doing In the video @Desert_AIP posted, and it seems to be working for him. Just cause it works doesn't mean it's code-correct though (I'm fairly sure this is a code violation, but not sure where in NEC it says it).

I would agree that this may not be code correct, but I think it is a safe way of doing it because the 30A breaker for AT will prevent an overload on the AT if, for some strange reason, it is balancing loads for an external customer.

 

[??????]

Great - so it sounds like post #44 single G/N bond in the service panel is getting close to being finalized, with the following additions:

• Lost neutral safety circuit
• Route inverter and subpanel grounds directly back to service panel G/N buss instead of through the GW (thoughts?)
• Conductor type and conduit annotations
• BOM
• Anything else?

@automatikdonn if you have your lucidchart file you could share, that might be good (unless anybody has anything more professional they could recommend). From there, I think it'd be good to throw this spaghetti against the wall with any electrician friends we collectively have, and then possibly we could nominate a brave soul to test it ?‍???

 

[automatikdonn]

Great - so it sounds like post #44 single G/N bond in the service panel is getting close to being finalized, with the following additions:

• Lost neutral safety circuit
• Route inverter and subpanel grounds directly back to service panel G/N buss instead of through the GW (thoughts?)
• Conductor type and conduit annotations
• BOM
• Anything else?

@automatikdonn if you have your lucidchart file you could share, that might be good (unless anybody has anything more professional they could recommend). From there, I think it'd be good to throw this spaghetti against the wall with any electrician friends we collectively have, and then possibly we could nominate a brave soul to test it ?‍???

I will be testing all of the failure modes, I have a service in my shop seperate from the house I don't mind tinkering with. And if something catches fire, I can at the very least see it and do something.

I am happy to share the outputs from lucidchart, also happy to share with other lucidchart users. It looks like this forum does not allow SVG attachments, so I uploaded the pdf.
What tools do most of you use to generate these types of docs? I have no windows, so I can't use visio (nor would I know how, I have been daily driving linux for 15ish years)

Here is a live view of the lucidchart doc that auto-updates when the doc is saved.

Wiring for Growatt 5000ES Mains and Gen Inputs: Lucidchart

Check out my Lucidchart document! Lucidchart is the intelligent diagramming solution that empowers teams to clarify complexity, align their insights, and build the future faster. Create your own diagram or flowchart at lucidchart.com.

lucid.app

Feel free to PM me your email address and I will add you to the lucidchart doc.

 

[automatikdonn]

How about this - it's not pretty. But I do believe it satisfies all of the requirements for a safe circuit.


Added Parts

230v Voltage Sensing Relay

https://www.amazon.com/dp/B087V4ZX9W

Not sure what contactor to use for the dry contact output on the GW

 

[??????]

Amazing work, thanks @automatikdonn ?

If anybody is feeling froggy, electra cloud looks like it might be a good option (free, cloud-based, versioned, sharable/forkable). Never personally used it. I think lucidchart does just fine for now though. I was using google charts and prior to that was using gliffy... would not recommend either.

Couple comments on post #50

• It looks like you're trying to switch grid neutral with the main service panel 4-pole contactor? If that's the case:
  • It looks like your neutral wire coming from the main service neutral to the contactor is green and I'd expect yellow
  • It looks like the the neutral conductor output from the contactor goes to the GW gnd and I'd expect it to go to the solar load service panel neutral buss
• I'd expect the GW AC IN gnd to tie directly to the main service panel neutral/gnd bonded buss, not pass through the 240V contactor
• GW dry contact relay for G/N bonding - what did you have in mind as a power source to drive this relay? Note: I've had good luck with 2-pole HVAC contactors for high current switching. I believe NEC 220.61 (screenshot below) says we need the ampacity of this relay (pole, not coil) to match our maximum unbalanced load, which for a single AT should be 30A. For a 240v coil, I think this 40A contactor should work for the G/N conditional subpanel bond.
  
  
• Nit: it looks like your AT overvoltage protection relay is monitoring one leg of the AT, my original post #12 monitors both legs (my redundancy is likely unnecessary... appreciate thoughts)

 

[automatikdonn]

The purpose in having the second contactor from main to GW inverter is to switch OFF all inputs from grid to GW in the event of a power loss. So this would be ground, and the two hots. When the power is shut to the GW from grid, this should engage the dry contacts of the GW triggering a Neutral Ground Bond on the Solar Disconnect service panel. That is at least the logic. Not sure how "up to code" this design is or the implications of essentially autoswitching a neutral ground bond, which is pretty much what is happening in this chart.

If there is no main panel electrically connected, then there is nothing to consider about G/N bonding and other what nots.


You are correct on only monitoring one leg and I don't know of an elegant way to solve that. Any ideas?

 

[automatikdonn]

Here is what I was able to find in the NEC, not sure if it applies to this scenario or not -

230.74 Simultaneous Opening of Poles

Each service disconnect shall simultaneously disconnect all ungrounded service conductors that it controls from the premises wiring system.

230.75 Disconnection of Grounded Conductor

Where the service disconnecting means does not disconnect the grounded conductor from the premises wiring, other means shall be provided for this purpose in the service equipment. A terminal or bus to which all grounded conductors can be attached by means of pressure connectors shall be permitted for this purpose. In a multisection switchboard or switchgear, disconnects for the grounded conductor shall be permitted to be in any section of the switchboard or switchgear.
Informational Note: In switchgear or multisection switchboards, the disconnecting means provided for the grounded conductor is typically identified as a neutral disconnect link and is typically located in the bus to which the service grounded conductor is connected.
250.6 Objectionable Current

(A) Arrangement to Prevent Objectionable Current

The grounding of electrical systems, circuit conductors, surge arresters, surge-protective devices, and conductive normally non-current-carrying metal parts of equipment shall be installed and arranged in a manner that will prevent objectionable current.

(B) Alterations to Stop Objectionable Current

If the use of multiple grounding connections results in objectionable current and the requirements of 250.4(A)(5) or (B)(4) are met, one or more of the following alterations shall be permitted:

1. Discontinue one or more but not all of such grounding connections.
2. Change the locations of the grounding connections.
3. Interrupt the continuity of the conductor or conductive path causing the objectionable current.
4. Take other suitable remedial and approved action.

250.8 Connection of Grounding and Bonding Equipment

(A) Permitted Methods

Equipment grounding conductors, grounding electrode conductors, and bonding jumpers shall be connected by one or more of the following means:

1. Listed pressure connectors
2. Terminal bars
3. Pressure connectors listed as grounding and bonding equipment
4. Exothermic welding process
5. Machine screw-type fasteners that engage not less than two threads or are secured with a nut
6. Thread-forming machine screws that engage not less than two threads in the enclosure
7. Connections that are part of a listed assembly
8. Other listed means

(B) Methods Not Permitted

Connection devices or fittings that depend solely on solder shall not be used.




I don't know if the actions being taken in the chart are approved, but they are seemingly suitable. I guess we will have to dive in and see if things work as expected. I have all of the parts listed on order

 

[LeRoyK]

Route inverter and subpanel grounds directly back to service panel G/N buss instead of through the GW (thoughts?)

I think this is a good idea. I checked and the Growatt has continuity between AC In Gnd, AC Out Gnd and Inverter case, so we only need to connect one of the inverters Gnd terminals.

second contactor from main to GW inverter

The purpose in having the second contactor from main to GW inverter is to switch OFF all inputs from grid to GW in the event of a power loss.

I believe you don't need this second contactor from main to GW inverter, it is just redundant to what is already build into the GW. The inverter has AC IN voltage sensing and will disconnect the internal contacts when the voltage is no longer good.

It will only disconnect L1 and L2, Gnd remains connected so that we do not have to add a second ground rod.

Switching N/G Bond with GW dry contacts

• I think this is a good idea, this prevents the AT from being paralleled to Grid Tansformer.

Not sure what contactor to use for the dry contact output on the GW

Use a 120V coil, you need to get power from a service panel, run it through the dry contacts then to the coil of the contactor.


N/G Bond
I had told you that you cannot have two N/G bonds at the same time, but that only applies to Inverter ON-Grid mode.
When Inverter is OFF-Grid the power source originates at the inverter, the original N/G Bond in the main service panel is no longer effective 'it is out of the curcuit'. So we need to create N/G Bond with the Contactor controlled by the GW dry contact. the two N/G bonds at the same time is fine. Being that the internal contacts in the GW have L1 and L2 disconnected, this puts the two N/G Bonds on completely different curcuits.

Lost Neutral Monitoring

Nit: it looks like your AT overvoltage protection relay is monitoring one leg of the AT, my original post #12 monitors both legs (my redundancy is likely unnecessary... appreciate thoughts)

I think it is fine monitoring only one leg if you monitor both Over Voltage and Under Voltage.

 

[automatikdonn]

Does anyone know an electrician we can get to review the design? It would be awesome to have an opinion from a licensed electrician who does these kinds of things (solar related) for a living.

I also plan on having my system inspected so I know if there are any code violations. Mainly for insurance purposes, if this all blows up and catches my shop on fire I want help in paying for the damages.

 

[automatikdonn]

I think this is a good idea. I checked and the Growatt has continuity between AC In Gnd, AC Out Gnd and Inverter case, so we only need to connect one of the inverters Gnd terminals.

second contactor from main to GW inverter

I believe you don't need this second contactor from main to GW inverter, it is just redundant to what is already build into the GW. The inverter has AC IN voltage sensing and will disconnect the internal contacts when the voltage is no longer good.

It will only disconnect L1 and L2, Gnd remains connected so that we do not have to add a second ground rod.

Switching N/G Bond with GW dry contacts

• I think this is a good idea, this prevents the AT from being paralleled to Grid Tansformer.

Use a 120V coil, you need to get power from a service panel, run it through the dry contacts then to the coil of the contactor.


N/G Bond
I had told you that you cannot have two N/G bonds at the same time, but that only applies to Inverter ON-Grid mode.
When Inverter is OFF-Grid the power source originates at the inverter, the original N/G Bond in the main service panel is no longer effective 'it is out of the curcuit'. So we need to create N/G Bond with the Contactor controlled by the GW dry contact. the two N/G bonds at the same time is fine. Being that the internal contacts in the GW have L1 and L2 disconnected, this puts the two N/G Bonds on completely different curcuits.

Lost Neutral Monitoring

I think it is fine monitoring only one leg if you monitor both Over Voltage and Under Voltage.

Ok so is this more like it? I put the neutral switching contactor in so the neutral is disconnected from the Solar disconnect panel in the event of a power failure. I am not sure its needed by happy path electric, but I thought it may be useful for unhappy path electric. One question about it, is should we also switch the ground on the same contactor?

I have also been searching for UL listed contactors. I found a couple on ABB such as this one - https://empower.abb.com/ecatalog/ec/EN_NA/p/1SBL177061R1401

 

[Desert_AIP]

If you pull the N from grid panel to derived panel, you're placing the autotransformer in parallel.
I still don't think you want to pull the N from the grid panel to the derived panel, even switched.
I don't think that is needed.
The only issue is the bonding. I do believe the bond in the derived panel should be switched, to activate when the grid is down.
The dry contact switch to activate the second bond in the derived panel when the grid goes down (or the GW switches to inverter power) is a good idea.

By not pulling the N from grid, the entire derived system is like a 240V appliance. And the safety ground still works through the path back to the grid panel, without a second bond.
The 120V side of derived system is powered through the autotransformer, which is itself a 240V appliance.

 

[LeRoyK]

Ok so is this more like it? I put the neutral switching contactor in so the neutral is disconnected from the Solar disconnect panel in the event of a power failure. I am not sure its needed by happy path electric, but I thought it may be useful for unhappy path electric. One question about it, is should we also switch the ground on the same contactor?
View attachment 70645

I don't think you need any Neutral wire and 'neutral switching contactor' from Main Service to Solar disconnect panel if you are using a contactor to Switch the N/G bond in 'Solar disconnect panel'. I had originally suggested having a Neural wire between Main Service and Solar disconnect panel to get away from the 'two N/G Bonds' problem, but that was before the N/G Bond switching contactor idea.

 

[automatikdonn]

How does the contactor for the N/G bond activate?

Is this getting closer?

 

[LeRoyK]

How does the contactor for the N/G bond activate?

Is this getting closer?
View attachment 70652

Connect the Red wire with "?" to your GW dry contact.
You are getting really Close!