Inverter Ground/Neutral Bonding

[JY99]

I am in an off-grid situation. My inverter provides AC power to a distribution panel which then controls circuits for my cabin. My question has to do with bonding neutral and ground in my panel. My inverter has DC inputs and a ground connection (currently bonded to my ground busbar which connects to a ground rod). For outputs, it has 2 AC outlets as well as a terminal AC block (with Live, Neutral, and Ground outputs).

When I plug in a standard outlet tester into the built-in AC outlets on the inverter it shows open ground and the GFCI testing button does not trip the circuit. I am getting the same results on outlets that I power through the breaker box (and hence the inverter AC terminal block). I am using standard breakers (non-GFCI). From what I understand, the means that my circuits are not ground protected and any GFCI outlets will not function properly. I have wired in a GFCI outlet onto one circuit and it does not function as a GFCI.

I then tried bonded the neutral and ground busbar in my panel and my outlets now seem to function properly (circuit tester says all good and the GFCI trip function works properly). I understand that bonding the ground and neutral in a subpanel can be a bad idea, but I'm not sure why, or if it is appropriate here.

Any information around the safest way to work with the AC side is greatly appreciated!

System Details
- Completely Off-grid
- 6, 12V-200 W panels; 2 panels connected in series to produce 24V, each pair connected in parallel
- Renogy 60 A MPPT charge controller
- 4, 24V LiFePO 100 Ah Renogy batteries
- 24 V - 2000 W inverter: https://www.amazon.ca/dp/B081YVNZX1?starsLeft=1&ref_=cm_sw_r_apan_dp_ZKTRH6YQV1ZDYXD4MF75

 

[Blakes]

I dunno much, but my Renogy 48v inverter with a cheap outlet tester always shows open ground regardless of my bonding the first (main) panel or not.

Out of curiosity, see if there is AC voltage across N and G on the inverter with it plugged into nothing but the batteries. I bet there is...

 

[sunshine_eggo]

You need exactly one N-G bond and G should go to earth (ground rod). Your inverter does not appear to supply it (smaller inverter-only units often don't).

You will probably measure significant AC voltage between G and N at the inverter.

 

[JY99]

You need exactly one N-G bond and G should go to earth (ground rod). Your inverter does not appear to supply it (smaller inverter-only units often don't).

You will probably measure significant AC voltage between G and N at the inverter.

So since my inverter does not have a N-G ground, should I then bond them in my breaker panel? My circuits all behave exactly as expected when I do bond them (GFCIs function when tested, circuit tester shows correct wiring, etc).

What is the hazard if there is a bond in both the inverter and the panel? I'm having trouble seeing what issues it would cause

 

[JY99]

I dunno much, but my Renogy 48v inverter with a cheap outlet tester always shows open ground regardless of my bonding the first (main) panel or not.

Out of curiosity, see if there is AC voltage across N and G on the inverter with it plugged into nothing but the batteries. I bet there is...

Hmmm... I'm not at my cabin now, but I will test next time I am there. How would having a voltage acorss the N and G mean in my case?

 

[Blakes]

How would having a voltage acorss the N and G mean in my case?

I can't answer that question directly.

I think that with voltage across N and G it causes the outlet testers to not work correctly. I'm in the same boat as you yet my system works 100% fine with all my electronics, saws, etc. It's ran 24x7 for about 3 years now.

 

[JY99]

I can't answer that question directly.

I think that with voltage across N and G it causes the outlet testers to not work correctly. I'm in the same boat as you yet my system works 100% fine with all my electronics, saws, etc. It's ran 24x7 for about 3 years now.

Did you bond N and G in your panel in your case? My appliances DID appear to work properly when N and G were unbonded, but I really want the protection of ground fault on my circuits (some outlets near my sink or outdoors, etc).

 

[Blakes]

Did you bond N and G in your panel in your case? My appliances DID appear to work properly when N and G were unbonded, but I really want the protection of ground fault on my circuits (some outlets near my sink or outdoors, etc).

Yes, I'm bonded on the main panel.

I went back and forth on the bonding. I was unbonded for a year or so, then only discovered that I have around 30V AC across N/G when installing a new outlet on an AFCI circuit that I turned off. That 30v AC was a little tingly.... So I bonded again.

Really, what I want/need is a UL listed inverter, but funds aren't there yet.

 

[JY99]

Yes, I'm bonded on the main panel.

I went back and forth on the bonding. I was unbonded for a year or so, then only discovered that I have around 30V AC across N/G when installing a new outlet on an AFCI circuit that I turned off. That 30v AC was a little tingly.... So I bonded again.

Really, what I want/need is a UL listed inverter, but funds aren't there yet.

Thanks! I am still confused on what the danger is from having an (potentially) extra N-G bond, but since my appliances work and my circuit tester works with them bonded in my panel, my limited knowledge suggests its the way to go.

 

[sunshine_eggo]

So since my inverter does not have a N-G ground, should I then bond them in my breaker panel? My circuits all behave exactly as expected when I do bond them (GFCIs function when tested, circuit tester shows correct wiring, etc).

What is the hazard if there is a bond in both the inverter and the panel? I'm having trouble seeing what issues it would cause

After reading the manual and seeing the asinine response to open ground troubleshooting, I'm convinced there is no N-G bond:

https://m.media-amazon.com/images/I/A1TUOcbM7YL.pdf

Additionally, per above, you will measure a voltage between N and G if there is none in the system.

Two N-G bonds will result in current on the ground wire. That will typically trip GFCI outlets all over the place.

 

[dopeassjackson]

You should be useing the breaker pannel bonding screw because your useing it on the main pannel. On a sub pannel the ground would be carried back in the ground wire to the main pannel.

The ground on the inverter outlet should be grounded all the way to the ground rod..which is what I believe you have done.

 

[Snapperhead]

I found this to be a great source of info on this exact topic, and have a question regarding this open also....

Grounding Made simpler - Part 1: AC/houshold grounding

To get the paper, click on the orange button at the top of the screen. The subject of grounding is a complex, multifaceted subject, that is often treated as an after-thought but needs to be considered from the beginning of the design and build...

diysolarforum.com

 

[TexanSun]

So since my inverter does not have a N-G ground, should I then bond them in my breaker panel? My circuits all behave exactly as expected when I do bond them (GFCIs function when tested, circuit tester shows correct wiring, etc).

What is the hazard if there is a bond in both the inverter and the panel? I'm having trouble seeing what issues it would cause

Bonding the neutral and ground in multiple locations allows for multiple paths and is called "circulating currents". That is an electrical flow that is unpredicable and would not be able to be an isolated path to ground. There is a potential for shock hazard as well as energized conductors, particularly neutrals where there should not be current flowing. Ground ONCE in the panel, regardless if supplied by grid or inverter. Carry ALL conductors, line, neutral and ground to the respective bus bars, breakers, switches within that one panel and its ONE path to ground

 

[Snapperhead]

Bonding the neutral and ground in multiple locations allows for multiple paths and is called "circulating currents". That is an electrical flow that is unpredicable and would not be able to be an isolated path to ground. There is a potential for shock hazard as well as energized conductors, particularly neutrals where there should not be current flowing. Ground ONCE in the panel, regardless if supplied by grid or inverter. Carry ALL conductors, line, neutral and ground to the respective bus bars, breakers, switches within that one panel and its ONE path to ground

@TexanSun Thanks for clearing this up..... Could you please cast your eye over my recent post re: "grounding loop" and let me know what you think. I'd really appreciate your input