How does your inverter deal with ground.

FilterGuy

What, me worry?
Folks, When setting up an inverter, one of the more important safety things to get correct is the grounding and the neutral-Ground bond.
  • All of the inverters have a grounding lug
  • All of the inverters have a ground connection on the AC out.
  • Some inverters have an AC in and when they do they have a ground connection on the input.
Sadly, the information provided in many manuals is nearly non-existent when it comes to how it handles ground internally.

Are the two (or three) grounds tied together?
Is there a neutral-ground bond?
If there is an AC-IN, does it change the neutral-ground bond when getting power from the AC-in?

I have started to try and collect this type of information for various inverters. Once I get information on several of them I will put it all into a resource and post it.

How does your inverter handle internal ground? If you send me the make/model of your inverter, I will add it to the resource.

The next 3 posts are examples of what I envision for each page of the resource.
 

adam.brakhane

New Member
I have the Growatt SPF 3000TL LVM and I thought it would operate pretty much as you describe the MPP solar LV2424, but from what I can tell, there is no way to enable a G-N bond on inverter power (the manual mentions an option #24 to enable this, but my inverter does not have option #24). Have you seen this one before?
 

DerpsyDoodler

Photon Sorcerer
i have a samlex evo 4024. neutral is bonded to ground internally. when ac is plugged in, neutral bond switches to ac neutral and ground is connected to input (earth ground) thereby also earth-grounding the RV. The samlex manual does an excellent job of explaining.
 

upnorthandpersonal

Administrator
Brand: MUST Power
Model: EP3000 Plus (European, 230V single phase, 6kW)
Source: me
Confidence: high

Are the two (or three) grounds tied together?

Yes

Is there a neutral-ground bond?

No

If there is an AC-IN, does it change the neutral-ground bond when getting power from the AC-in?

No

In Europe, it is generally not done - TT networks are actually growing due to RCDs being very good and readily available. It depends of course from country to country here...
 

Comanchecreek

New Member
Power Tech On 2000 watt inverter. No neutral ground bonding that I can test. No reference to grounding in manual other than to ground the bonding lug to trailer frame. Causes GFCI trip when first powered on. No AC input, only DC. Installed in a fifth wheel trailer. Connection to the trailer is plug in through 50 amp plug using a 20 amp adapter. Large draws, and converter/charger portion of converter is turned off. Large draw items such as refrigerator, and A/C unit are shut off.
 

FilterGuy

What, me worry?
I have the Growatt SPF 3000TL LVM and I thought it would operate pretty much as you describe the MPP solar LV2424, but from what I can tell, there is no way to enable a G-N bond on inverter power (the manual mentions an option #24 to enable this, but my inverter does not have option #24). Have you seen this one before?
I Have had a *really* hard time getting any definitive data on growatt inverters. I would love to get my hands on one and figure it out.
Brand: MUST Power
Model: EP3000 Plus (European, 230V single phase, 6kW)
Source: me
Confidence: high

Are the two (or three) grounds tied together?

Yes

Is there a neutral-ground bond?

No

If there is an AC-IN, does it change the neutral-ground bond when getting power from the AC-in?

No

In Europe, it is generally not done - TT networks are actually growing due to RCDs being very good and readily available. It depends of course from country to country here...
Thanks!!! I will add this to the resource.
 

Aquanuts

New Member
Folks, When setting up an inverter, one of the more important safety things to get correct is the grounding and the neutral-Ground bond.
  • All of the inverters have a grounding lug
  • All of the inverters have a ground connection on the AC out.
  • Some inverters have an AC in and when they do they have a ground connection on the input.
Sadly, the information provided in many manuals is nearly non-existent when it comes to how it handles ground internally.

Are the two (or three) grounds tied together?
Is there a neutral-ground bond?
If there is an AC-IN, does it change the neutral-ground bond when getting power from the AC-in?

I have started to try and collect this type of information for various inverters. Once I get information on several of them I will put it all into a resource and post it.

How does your inverter handle internal ground? If you send me the make/model of your inverter, I will add it to the resource.

The next 3 posts are examples of what I envision for each page of the resource.
I have an AIMS 24vdc to 115vac 1500W/3000W pure sine wave. I have been having an issue do to it being under powered, unrelated to this thread but during the course of troubleshooting the problem I discovered that a circuit checker indicates an open ground. AIMS Tech Support says that is a normal reading as the neutral line carries voltage, (I didn't get the value), and must be left to float from ground. He also said that connecting the neutral to ground would damage the inverter. I have the inverter installed such that it will supply the a/c needs of my trailer unless there is a shore power supply, in which case there is a relay that isolates the inverter from the A/C network. Apparently, that is the right way to do it. I would say that you should tie your system ground to the chassis and leave you neutral float. Isolate your inverter from AC when you are on shore power, (I believe that is code anyway) since the neutral will be tied to ground at the supply panel.

My 2 cents worth.
 

DerpsyDoodler

Photon Sorcerer
I have an AIMS 24vdc to 115vac 1500W/3000W pure sine wave. I have been having an issue do to it being under powered, unrelated to this thread but during the course of troubleshooting the problem I discovered that a circuit checker indicates an open ground. AIMS Tech Support says that is a normal reading as the neutral line carries voltage, (I didn't get the value), and must be left to float from ground. He also said that connecting the neutral to ground would damage the inverter. I have the inverter installed such that it will supply the a/c needs of my trailer unless there is a shore power supply, in which case there is a relay that isolates the inverter from the A/C network. Apparently, that is the right way to do it. I would say that you should tie your system ground to the chassis and leave you neutral float. Isolate your inverter from AC when you are on shore power, (I believe that is code anyway) since the neutral will be tied to ground at the supply panel.

My 2 cents worth.
There is no "1 size fits all" solution to this. you have to know how your inverter handles grounding to understand how to properly ground it for your use case.

This sounds like good info for other users of aims inverter(s).
 

FilterGuy

What, me worry?
I have an AIMS 24vdc to 115vac 1500W/3000W pure sine wave. I have been having an issue do to it being under powered, unrelated to this thread but during the course of troubleshooting the problem I discovered that a circuit checker indicates an open ground.
Interesting. What model do you have? According to the manual for the LV2424 inverter/charger this is conceptually the way it should work:

1627067511236.png

(Unlike many companies, Aims documented the LV2424 grounding scheme pretty well.)
As you can see, When on battery, the LV2424 creates the N-G bond and when on shore power it does not. This is pretty standard for a good inverter/charger because you always want one and only one N-G Bond and shore power should always have a N-G Bond.

AIMS Tech Support says that is a normal reading as the neutral line carries voltage, (I didn't get the value), and must be left to float from ground. He also said that connecting the neutral to ground would damage the inverter.
That seems like a really bad design for an inverter. It completely prevents one of the primary purpose of the 'ground' wire in the AC wiring from working: A short to the ground wire will not pop the breaker and clear the fault.
 

Leon

Solar Enthusiast
I've recently received one of these 3.5KW all in one units (will be inverter-only usage in my case): aliexpress link

Is there a set of tests I can do to conclusively work out the grounding arrangements? The manual and user interface is clearly derived from the same source as MPP etc, for what that is worth.
 

FilterGuy

What, me worry?
I've recently received one of these 3.5KW all in one units (will be inverter-only usage in my case): aliexpress link

Is there a set of tests I can do to conclusively work out the grounding arrangements? The manual and user interface is clearly derived from the same source as MPP etc, for what that is worth.
lets walk through it.

Ground:
Every inverter I have looked at or have the information for has the Chassis Ground, AC input Ground, and AC output ground all tied together. You can check this with an ohm meter.

As a 240 V unit, you will still have a neutral and a Hot.... I do not have the manual so I can't really say how it is marked.

Neutral-Ground Bond.
This gets a little tricky because you don't know what relays are internal to the inverter and what the 'non-powered' state of the relay is.
When the inverter is hooked up you can put an AC voltmeter between neutral and ground. If there is a voltage higher than a few milivolts, there is probably not a N-G bond. If the voltage is zero or just a few milivolts, there probably is a N-G bond.

Since it is a 240V Single phase output, my guess is that you will find that there is no N-G bond. However, if you are putting in an off-grid system you need to decide what your grounding scheme will be. The key question will be 'Will the breaker trip if there is a short between the Hot and ground/safety wire. One way to accomplish this is to create a N-G bond at the inverter. In the event of a short, the bond will alow a high current that will trip a traditional breaker and clear the fault. However, people have reported that some manufacturers say not to do this or it will damage the inverter. (That seems like a bad design to me and I sometimes wonder if the call agent does not really know what they are talking about).

Another way to 'clear the fault' is to use CGFI breakers that will trip if the current in the hot and neutral become unbalanced.

The key is to have one and only one NG-bond in the system. If you have an inverter set up and there is an external N-G ground, you can check to see if there is an internal N-G bond by putting a clamp on ammeter on the ground wire between the inverter and the external N-G ground while there is an AC load on the system. If there is current on the ground wire, then the inverter almost certainly has an internal N-G ground and the external N-G ground should be removed. (Note: That current on the ground wire is a safety issue and is why you should not have more than one N-G ground.

Note: In all of the discussion so far in this post, the term 'ground' has almost nothing to do with earth ground. It is talking about the grounding wire that is throughout the AC system (In the US, this is called the Equipment Grounding Wire) The tests are the same regardless if the ground wire is tied to earth.

The primary purpose of tying the ground wire to earth ground is to ensure the system does not 'float' to a voltage that is significantly higher than the earth.

Since you will only be using it as an inverter this does not apply, but the issue gets more complicated if you are using 'shore power'. Since shore power [almost] always has a N-G bond, there should be no additional N-G bond when on shore power. However, when you are not on shore power, there needs to be a bond. Some inverters handle this with relays. Some don't handle it at all.
 

OffGridInTheCity

Solar Addict
At the US AC level I believe I understand and all my stuff is grounded. Its the DC side - e.g. the battery - that I don't get. I have a 48vdc system.

In general what's the logic of DC ground vs AC ground - can they be shared? should thy be different? does DC need to be grounded?

I have AIMS 12,000w inverters and I ground the AC output to the regular house ground, do not use the AC input (so not ground needed) - but don't do anything on the 48vdc battery side.
 
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FilterGuy

What, me worry?
The NEC requires any circuit operating above 50V to be grounded. A Nominal 48V system will run as high as 60V so the NEC requirement is that it must be grounded.

Ideally you would have all of the grounds for your DC equipment on one ground bus. The DC negative would also be tied to this bus. Meanwhile, all of your AC equipment ground are on a 2nd ground bus. A single wire between one of the two buses tie them together. Typically the AC ground bus would also be tied to earth ground....meaning the DC ground is tied to earth ground as well.

Note: I typically find the best way to tie the DC ground bus to the AC ground bus is to tie the ground lug of the inverter to the DC ground bus. Since the inverter ties AC ground to the lug, this ties the AC grounding to the DC grounding.

You may want to review this series of resources:
 
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