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Set me straight on neutral/grounding on input

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(@collin80)
Active Member
Joined: 3 years ago
Posts: 4
Topic starter  

Yes, I know this has been discussed before. I read the existing topics. I think I'm just not getting my head around the concept fully. I can do the test suggested where I try stuff while the unit is off but I thought I'd ask for my specific set up and see if I'm just being dumb. Currently there is a 4 wire cable running between two breaker boxes in my house and I'd rather not cut it until I'm sure of what I really ought to do.

I don't have solar set up yet (got the panels.... I'll install them some day). For now I want to use the GS6k unit as essentially a battery back up for my secondary panel that runs my upstairs. I have batteries hooked up and have been using the inverter for testing purposes with the batteries powering the load. I charge the batteries with an external charger any time they get low. Now I want to actually... use the inverter properly. So, I want to connect to the incoming AC power and run it through the inverter to my secondary panel.

I've read about how the use of split phase input is problematic. Now, currently my subpanel is fed via 4 wires from my main panel. Obviously the main panel by code has neutral and ground bonded at the panel. If I were to disconnect the main and sub panels and wire the GS6k in between I think I'm supposed to attach L1 and L2 from the main to the input of the inverter, perhaps also attaching ground to the ground of the inverter then leave neutral input disconnected and attach the L1, L2, neutral of the subpanel to the output of the inverter. The inverter having a center tapped transformer should then provide the appropriate neutral for the subpanel. What I worry is what happens with ground. Technically it's connected to neutral. If I attach ground to the subpanel then the sub panel is sort of getting the original input neutral, right? This seems like it's perhaps not the way to go. Though, as long as neutral and ground are physically separate in the sub panel (and they ought to be!) then really I guess I'm not getting the neutral bleed through.

 

So, I hope the reader's digest version of what should be done is:

1. Ground/Neutral bond the main panel

2. On the inverter input only L1 and L2 but cap off the input neutral

3. Connect the ground of the main panel to the ground of the inverter

4. Connect L1, L2, N of output of inverter to a sub panel.

5. Connect ground from inverter and input to ground of sub panel such that this ground is completely 100% separate from any and all neutrals

 

Is that accurate?

 


   
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(@dickson)
Noble Member
Joined: 4 years ago
Posts: 1048
 

If I were to disconnect the main and sub panels and wire the GS6k in between I think I'm supposed to attach L1 and L2 from the main to the input of the inverter, perhaps also attaching ground to the ground of the inverter then leave neutral input disconnected and attach the L1, L2, neutral of the subpanel to the output of the inverter. The inverter having a center tapped transformer should then provide the appropriate neutral for the subpanel. What I worry is what happens with ground.

Make sure  L1  and L2  of the main  is only  connected to the GS 6k  INPUT .   The output of the inverter is  connected  to the subpanel L1  N  L2  .   The inverter having a center tapped transformer should then provide the appropriate neutral for the subpanel.   The  N  from the  main  is also  connected to the subpanel .   What happen with the ground  is  Connect the ground of the main panel to the ground of the inverter and  to the ground of the subpanel  but not  to the neutral  in the subpanel which go back to the  inverter .  The  ground rod at the main  will provide ground for the inverter  and  subpanel   and  the  N  of the transformer  .   This is similar   in  Genetry Solar Inverter 'ATS' (grid backup) mode demonstration  youtube  video .  You need  the  rev C  control board  .   The  main L1  and L2  is not  connected to the subpanel  but  L1 and L2  is  connected to the  subpanel  for (grid backup) to work .   


   
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(@inphase)
Estimable Member
Joined: 4 years ago
Posts: 159
 

Since the transformer in the inverter electrically isolates the input from the output, you will have what the code calls a "Separately Derived System". As such, you have to connect the output neutral to a "grounding electrode". You already have a grounding electrode system in the building at the original service. Any new electrode system has to bond to that one. So essentially the two system neutrals will end up connected together. In order to have an effective ground fault path, the output neutral will need to be connected to ground in your panel. If you already have a grounding electrode conductor present, then you are golden.


   
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(@collin80)
Active Member
Joined: 3 years ago
Posts: 4
Topic starter  

It sounds like my first step is getting a rev C control board as I've got a B board and that sounds to not work. I know you cannot have the neutral connect up on the B board if you're using split phase 240v - which I am.


   
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(@sid-genetry-solar)
Member Admin
Joined: 4 years ago
Posts: 2883
 
Posted by: @collin80
It sounds like my first step is getting a rev C control board as I've got a B board and that sounds to not work. I know you cannot have the neutral connect up on the B board if you're using split phase 240v - which I am.

In a nutshell, yes.  It is possible to use an A.1 / B board with a 240v setup, as long as the Neutrals are separated between the input panel and the output loads--i.e. as long as there are only 2 wires from the "input" power source connected to the inverter. 

You can check for a backfeed condition without damaging the inverter, providing it's powered off.  If you apply power to the AC input (WITH THE INVERTER OFF), measure the voltage on the output terminals.

  • If it's 0vAC, you're good.
  • If it's 240vAC, there's a backfeed condition due to the neutrals being tied together. 

This test will not hurt the inverter as long as it is powered off.


   
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(@dickson)
Noble Member
Joined: 4 years ago
Posts: 1048
 

I don't have solar set up yet (got the panels.... I'll install them some day). For now I want to use the GS6k unit as essentially a battery back up for my secondary panel that runs my upstairs. I have batteries hooked up and have been using the inverter for testing purposes with the batteries powering the load. I charge the batteries with an external charger any time they get low. Now I want to actually... use the inverter properly. So, I want to connect to the incoming AC power and run it through the inverter to my secondary panel.

Watch  ( Rev C input output requirements. Seek professional install! )   the latest  youtube  video  if  you  want to connect to the incoming AC power and run it through the inverter to your  secondary panel.      Your secondary panel that  run the upstair  must be  totally disconnected  from the  main panel   L1 and L2  .  The main  L!  and L2   is  connected to the  GS 6kw  INPUT  so your main  is  always ON  and not shut off like Sean  do in the video .    Be  careful  or your  inverter will have a very bad day .  


   
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