Transfer switch giving me choice of grid or solar

[bigbass57]

Attached is a drawing of my layout. Just seeing if anyone sees any issues with my process. I have 5 EG4 6000XP inverters all hitting a combiner panel with each on 40a breakers. Out of this combiner panel I go to my transfer switch (Siemens DTNF324R by the way I'm switching my neutral so nothing goes back to the grid). Also going into transfer switch is my grid power so I can choose between Grid and solar. And of course the load comes out to my house's main panel. As you can see I left my disconnect this is my first line of disconnect and we are bonded at this location. Past that all my neutrals and grounds are separate. To add, I have a 27 KW generator that connects to the inverters and is auto started if my batteries need charging when the panels are not enough. I'm open to any ideas or suggestions. I know there are many ways to achieve this process. Just want to be certain I'm doing things correctly and safely. Thx

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[Azengr]

Maybe I missed it, but where is the neutral-ground bond when the transfer switch is feeding from inverter? Will you have the bond done on the primary inverter?

 

[bigbass57]

Maybe I missed it, but where is the neutral-ground bond when the transfer switch is feeding from inverter? Will you have the bond done on the primary inverter?

Sorry, I got so carried away explaining my system I forgot to ask my main question. Do I ground Bond in my inverter combiner panel or do I enable the ground bond within the menu of my EG4 inverters? Or does it matter where it bonded Inverter menu or combiner panel? Seems to me when I transfer from grid to solar I will need ground bond for my main panel since it is not ground bonded. My ground bonding for grid occurs at my grid disconnect so I know I'm good there. By the way my transfer switch will switch my L1 and L2 as well as my neutral. I felt like if I did not switch my neutral I may have some kind of back feed possibly to the grid. Thx

 

[ricardocello]

Sorry, I got so carried away explaining my system I forgot to ask my main question. Do I ground Bond in my inverter combiner panel or do I enable the ground bond within the menu of my EG4 inverters? Or does it matter where it bonded Inverter menu or combiner panel? Seems to me when I transfer from grid to solar I will need ground bond for my main panel since it is not ground bonded. My ground bonding for grid occurs at my grid disconnect so I know I'm good there. By the way my transfer switch will switch my L1 and L2 as well as my neutral. I felt like if I did not switch my neutral I may have some kind of back feed possibly to the grid. Thx

It takes two wires to feed anything back to the grid, a single neutral won't do it.
Nevertheless, the 3-pole transfer switch will work fine, but a 2-pole is all that is needed.

Here's an interesting point to consider: When you put the ground bond for the inverter in place (either in the inverter, or a hard connection in the transfer switch, you would be effectively connecting the grid neutral to the inverter neutral through the ground wire anyway. Defeating the purpose of the 3-pole switch.

The only way to prevent that is to do a single N-G bond either in the transfer switch on the load N, or in the main panel.
However, I believe code specifies that the bond should be at the first disconnect. @timselectric ?

 

[bigbass57]

It takes two wires to feed anything back to the grid, a single neutral won't do it.
Nevertheless, the 3-pole transfer switch will work fine, but a 2-pole is all that is needed.

Here's an interesting point to consider: When you put the ground bond for the inverter in place (either in the inverter, or a hard connection in the transfer switch, you would be effectively connecting the grid neutral to the inverter neutral through the ground wire anyway. Defeating the purpose of the 3-pole switch.

The only way to prevent that is to do a single N-G bond either in the transfer switch on the load N, or in the main panel.
However, I believe code specifies that the bond should be at the first disconnect. @timselectric ?

Totally agree. I was concerned as where to make my ground bond for the solar panel since the inspector wants ground bond at my disconnect before the transfer switch. This means I don't have ground bond at my main panel and would need it somewhere along the way for my solar panel to operate correctly. I don't have any history with ground bonding using the menu of the EG4 6000XP so I thought I could ground bond at the solar combiner panel. I heard Will speak about bonging in the menu but not sure how that occurs or works. Back to the transfer statement, I probably could save money getting a 2 pole instead of three pole transfer. I returned my three pole until I could get more clarity on the situation. Thx

 

[timselectric]

Your N/G bond already exists at the main panel. Do not add one.
And the transfer switch should only switch the line conductors. Not the neutral or ground.

 

[bigbass57]

Your N/G bond already exists at the main panel. Do not add one.
And the transfer switch should only switch the line conductors. Not the neutral or ground.

Thx

 

[Azengr]

I went through a similar design iteration process, initially planning to use a 3-pole manual transfer switch before ultimately going with a 2-pole switch, “saving” money and not trying to mess with the whole switching neutral and N-G bond challenges.

Not sure if it is useful, but below is what I ended up building. Couple differences to your plan: I only have 2x6000xp, I utilize the grid input on the inverters as I don’t have enough panels to be fully independent, and I run the generator input through a transfer switch to either feed my inverters (normal) or directly feed my load panel (something would have gone really bad for this scenario - I already had the 100A switch sitting around). My main challenge was trying to design in a way that avoided neutral and ground loops. Feel free to use for inspiration at your own risk… I’m not an electrician.

Out of curiosity, why go with 5 x 6000xp inverters instead or 2 or 3 x 12000xp?

 

[bigbass57]

I went through a similar design iteration process, initially planning to use a 3-pole manual transfer switch before ultimately going with a 2-pole switch, “saving” money and not trying to mess with the whole switching neutral and N-G bond challenges.

Not sure if it is useful, but below is what I ended up building. Couple differences to your plan: I only have 2x6000xp, I utilize the grid input on the inverters as I don’t have enough panels to be fully independent, and I run the generator input through a transfer switch to either feed my inverters (normal) or directly feed my load panel (something would have gone really bad for this scenario - I already had the 100A switch sitting around). My main challenge was trying to design in a way that avoided neutral and ground loops. Feel free to use for inspiration at your own risk… I’m not an electrician.

Out of curiosity, why go with 5 x 6000xp inverters instead or 2 or 3 x 12000xp?

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Wow!! Really helpful. This gives me some insight to improve. I ordered the 2 pole today instead of the 3 pole. To answer your question on inverters, I had the 6000EX and I had an offer to upgrade to the 6000XP at the time for little to no cost. I did consider the 12k and 18k but did not want to lay out the money. I did not do solar for a ROI situation as my zero base home build does not have more than $140 monthly grid cost running all electric with 2 large mini splits, tankless hot water, and a double oven range among other normal household items. Sometimes we are under $100 a month. We can experience grid down for a week or two with ice and snow issues. I have to say they have really improve the system and of course I'm underground which helps but down the road it is power lines on poles. Seems as though we have had no grid down since adding all this solar system. We are currently running 12k in PV with plans to expand. I do have a 27kw Generac to charge batteries when needed. Thanks for the drawing and input, I truly appreciate it.