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Grounding sub panel

Marqese

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Feb 18, 2022
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I’m now at the point of wiring up my growatt to a sub panel. On the growatt Im wiring the AC input to an extension cord that I will plug into a grid tied outlet. From the AC output Im wiring a sub panel. My question is where does the ground from the AC output of the growatt connect to in the sub panel?
 
The metal chassis of ALL devices in the system should be grounded and the ground should trace all the way back to the MAIN panel. Specifically to your question. The Growatt should have a grounding lug, hopefully 2. The ground wire from the extension cord going to the Growatt AC INPUT should be attached to the Growatt ground lug and the the other ground lug (add one if needed) on the Growatt should be attached to the ground bus bar of the sub-panel. You didn't mention a neutral wire. If there is a neutral going into the sub-panel then make sure the ground bus and neutral bus are NOT tied together.
 
Thanks for the response. What’s weird is my sub panel didn’t come with a ground bus which I thought was weird. It has the neutral bar so I’m good there
 
Thanks for the response. What’s weird is my sub panel didn’t come with a ground bus which I thought was weird. It has the neutral bar so I’m good there
Midnight Solar has a nice selection of bus bars. You should size the ground bus so it has the same number of positions as the number of branch circuits that will be in the sub-panel because each of these should be grounded also.
 
Make sure the ground bar is bonded to the casing of the sub panel and the neutral bar is isolated from casing. Some sub panels will have a green machine screw going through the neutral bar or buss that bonds it to the casing.
 
The heavy powder coating is basically non conductive unless you sand off a small area down to bare metal. If you attached the Ground Bus Bar to the panel with the self threading metal screws then it should be fine.
 
Boxes need to be grounded with wires (typically green for U.S.) to terminal lug, sheet metal screwed into metal case. Metal conduit between boxes does not qualify as grounding two boxes together because their threaded collar clamping rings often become loose, potentially making poor connection.

Think about consequences not grounding separated electrical metal boxes together. Left hand on one metal box, right hand on another metal box. Do you feel lucky or confident?

Grounding together metal electrical boxes is for safety and should be non-negotiable, but it is not going to solve any neutral to ground bonding issue that it might create with your inverter due to the single point ground to neutral bonding in main panel. Actual outside ground rod connection should only go to one point which is normally main input breaker panel.

Neutral should be brought back to single point neutral-ground bonded neutral bus bar in breaker box (typically main box). If you make any additional neutral to ground bonding in downstream boxes then you can have neutral return currents being shared on ground wires, which is a no-no, also creating a safety issue.
 
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Boxes need to be grounded with wires (typically green for U.S.) to terminal lug, sheet metal screwed into metal case…Grounding together metal electrical boxes is for safety and should be non-negotiable,
posts 2&6 mention that as well

To OP: I would insure the metal box has 0 ohms to the grounding bus bar. You have to test on bare metal as someone mentioned

neutral bar doesn’t have continuity to the panel either though. This is the sub panel I have
And it should not - as a sub-panel

The neutral(s) should be joined together with neutrals only; the bare/green/grounds should be joined only to themselves; there should be only one place that neutrals and bare/green meet to be joined together and that is specifically called out to be at the power source.
My question is where does the ground from the AC output of the growatt connect to in the sub panel?
Do the instructions received with your unit have a wiring diagram? Because I don’t know if your growatt makes a neutral-ground bond or not.
1) If your sub-panel does not “see” the neutral-ground bond in the main panel that supplies the growatt and the growatt doesn’t make one the instructions should address that.
2) if the growatt output neutral and ground are bonded then you’ll want to address that with the instructions for the unit.
Make sure the ground bar is bonded to the casing of the sub panel and the neutral bar is isolated from casing. Some sub panels will have a green machine screw going through the neutral bar or buss that bonds it to the casing.
I’m not sure but I’m reasonably sure that boxes sold as subpanels do not usually have the neutral bonded to the box. But I’m not an electrician so my experience is limited for panels. You can add ground busbars for convenience but for small numbers of breakers I think code allows bare/grounds (with a jumper to the box) to be joined in the subpanel with wire nuts. At least one electrician I hired did that in a commercial building and the inspector signed off… but what do I know?
 
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posts 2&6 mention that as well

To OP: I would insure the metal box has 0 ohms to the grounding bus bar. You have to test on bare metal as someone mentioned


And it should not - as a sub-panel

The neutral(s) should be joined together with neutrals only; the bare/green/grounds should be joined only to themselves; there should be only one place that neutrals and bare/green meet to be joined together and that is specifically called out to be at the power source.

Do the instructions received with your unit have a wiring diagram? Because I don’t know if your growatt makes a neutral-ground bond or not.
1) If your sub-panel does not “see” the neutral-ground bond in the main panel that supplies the growatt and the growatt doesn’t make one the instructions should address that.
2) if the growatt output neutral and ground are bonded then you’ll want to address that with the instructions for the unit.

I’m not sure but I’m reasonably sure that boxes sold as subpanels do not usually have the neutral bonded to the box. But I’m not an electrician so my experience is limited for panels. You can add ground busbars for convenience but for small numbers of breakers I think code allows bare/grounds (with a jumper to the box) to be joined in the subpanel with wire nuts. At least one electrician I hired did that in a commercial building and the inspector signed off… but what do I know?
You can find panels with neutral bond connections. Almost any panel can be used as a "Main" especially anything rated for 100 amps or more. It depends on the application. A small 6 circuit panel that has a breaker backfed from a meter to supply a single water pump for livestock would be considered the main.
You should never use wirenuts in a panel.
 
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