inverter grounding question

elesaver · July 2014

There is something on these forums that talks about redundancy in grounding for some inverters.

Here's the story: I will be using a 1500W Cotek 24V inverter. It has a grounding lug on top. Meanwhile, I will be running a wire from the inverter to a disconnect box and then to a small panel for up to 6 circuits. It is not clear to me as to where I should do the grounding...with the inverter lug or at the panel...or both?

If you decide to try to teach me (which I hope someone will), be as basic as you can since my experience is somewhat lacking. Thanks in advance.

Cariboocoot · July 2014

Re: inverter grounding question

There are three things that should be grounded on a sine wave inverter:
1). The DC negative
2). The metal case
3). The AC Neutral output (N-G bond)

Now here's where it gets tricky: some inverters have outlets on them and already have the N-G bond built-in. Thus the metal case gets grounded and that also grounds the AC Neutral output.

If you feed the output of the inverter to an AC distribution panel there will be grounds collected there from the branch circuits. They also need to be connected to ground, along with the distribution panel's case (usually there is a ground bus bar in the case bonded to it). But, and this is important, you do not want a neutral-ground bond in the distribution panel if one already exists at the inverter.

elesaver · July 2014

Re: inverter grounding question

"But, and this is important, you do not want a neutral-ground bond in the distribution panel if one already exists at the inverter. "

And, how would I go about discovering if there is a neutral-ground bond already existing in the inverter?

Cariboocoot · July 2014

Re: inverter grounding question

elesaver wrote: »

"But, and this is important, you do not want a neutral-ground bond in the distribution panel if one already exists at the inverter. "

And, how would I go about discovering if there is a neutral-ground bond already existing in the inverter?

First, check the installation manual to see what it has to say on the matter.
Second, one clue would be if it is hard-wired (usually no bond) or has outlets (usually bonded).
Third, with everything unwired and powered down check for continuity between neutral and ground.

BB. · July 2014

Re: inverter grounding question

Reviewing the manual, taking the output cover off and looking at the terminal/outlet block, using an Ohm meter, etc...

It is usually pretty obvious if they grounded the Neutral of the AC output (green wire connected to AC white or other color output wire).

If you have a generator permanently wired--You should also review its manual/grounding too. Generators tend to be larger animals and it can be a bit more difficult to find the a ground bonded AC neutral.

Generators over ~3.5 kWatts seem to usually have the ground bonded neutral. Smaller generators tend not to (may be somewhere in the US National Electric Code).

Two ground bonds is not the end of the world... But can cause problems--Particularly if you have a GFI type outlet on the genset or AC inverter. The two bondings will tend to trip the GFI in the middle.

Also--I am not a fan of GFI on the input to an AC Main panel... I prefer to have the GFI at the point of use (near sink, outside, etc.). That way, if a GFI is tripped, you know (roughly) where it occurred--And your entire home/RV is not plunged into darkness because the main/only GFI back at the inverter/genset was tripped.

-Bill

elesaver · July 2014

Re: inverter grounding question

OK, Cariboocoot and Bill. Thanks for the instruction. I will begin checking this out tomorrow.

zoneblue · July 2014

Re: inverter grounding question

Basically the inverter (aswell as all other metal cased components) should have its case connected to a single earth bus bar. That earth bus is then connected directly to the earth stake. You should avoid multiple, daisy chained, or joined grounding conducters. The exception would be an inverter with a double insulated plastic case, like my Stecca. The size of the inverter grounding conducter should be large enough to carry expected fault currents.

elesaver · July 2014

Re: inverter grounding question

After looking more closely into the Cotek SK1500 manual, I have found grounding information. The section reads:
Section 3-6
"The AC output ground wire should go to the grounding point for your loads (for example, a distribution panel ground bus).
Section 3-6-1
"120V models: The neutral conductor of the AC output circuit of the inverter is automatically connected to the safety ground during inverter operation. This conforms to NEC requirements that separately derived from AC sources (such as inverters and generators) which have their neutral conductors tied to ground in the same way as the neutral conductors from the utility tied to ground at the AC breaker panel. For models configured with a transfer relay while AC utility power is present and the inverter is in bypass mode, this connection (the neutral of the inverter's AC output to input safety ground) is not present so that the utility neutral is only connected to ground at your breaker panel, as required."

All right. Now, is my interpretation of this info correct? (I am plugging a male plug into the inverter by the way. This seems better than hard wiring at this moment because, in time, I hope to get a larger inverter. Anyway, the male plug will be attached to 10/2 wire and extend approx 50' to the location of the a disconnect box prior to being fed to a new electrical panel. At that panel, I will attach the ground wire from the 10/2 wiring to the ground bus bar which, in turn, will be attached to a earth grounding pipe. The grounding lug available on the inverter will not be used.

It's Section 3-6-1 Somewhat confusing to me with my application. I need some instruction on this, if you wouldn't mind. I will be running the 120V inverter panel to a breaker panel but never connected to the main AC utility where that box is grounded. I plan to ground the solar breaker panel from the ground bus bar to the same earth ground post that the main panel uses but with its own wire and clamp, of course.

Did I bat 1.000? Or should I go back to the drawing board?

Cariboocoot · July 2014

Re: inverter grounding question

"120V models: The neutral conductor of the AC output circuit of the inverter is automatically connected to the safety ground during inverter operation."

That means the neutral-groud bond is present at the inverter and does not need to be duplicated at the breaker panel.

Likewise this bond would be present in the main service panel, so if you were to use a transfer switch to change the sub panel between inverter and grid it would switch both hot and neutral; the N-G bond would change location but still be present. Hence this from the manual:

"For models configured with a transfer relay while AC utility power is present and the inverter is in bypass mode, this connection (the neutral of the inverter's AC output to input safety ground) is not present so that the utility neutral is only connected to ground at your breaker panel, as required."

Although that is meant for inverters with built-in transfer switches it is good to know they are trying to make the maze of wiring clear.

"The AC output ground wire should go to the grounding point for your loads (for example, a distribution panel ground bus."

That simply means to connect the ground wiring of loads (i.e. outlets) to the ground connection of the inverter. This is standard "carry through" wiring: hot to hot, neutral to neutral, ground to ground.

Carry the grounds from loads to the inverter, ground the inverter to Earth (this can even be a ground connection to the main service panel). You're good.

elesaver · July 2014

Re: inverter grounding question

"Carry the grounds from loads to the inverter, ground the inverter to Earth (this can even be a ground connection to the main service panel). You're good."

Thank you, Cariboocoot. I think I've got it. I'll run the inverter 120V to a disconnect and then to the 2nd smaller panel that is going to use solar power only (not connected in any way to the main panel). I'll earth ground that (solar power) electrical panel. I do not need to use the inverter grounding lug.

gkar · August 2014

Re: inverter grounding question

Cariboocoot wrote: »

There are three things that should be grounded on a sine wave inverter:
1). The DC negative
2). The metal case
3). The AC Neutral output (N-G bond)

That answered my neutral/ground bond question. I just bought a Schneider Electric Conext SW 2524 2,500 Watts, 24VDC Inverter/Charger for Split-phase 120/240 VAC and their manuals never covered the topic. In fact their wiring diagrams didn't show a neutral/ground bond.

I ohmed out the case ground stud to the neutral on the output and it was open. So should I bond the ground and neutral at the main distribution/breaker box (standalone, isolated system in a shed for a 240v well pump)?

Cariboocoot · August 2014

Re: inverter grounding question

gkar wrote: »

That answered my neutral/ground bond question. I just bought a Schneider Electric Conext SW 2524 2,500 Watts, 24VDC Inverter/Charger for Split-phase 120/240 VAC and their manuals never covered the topic. In fact their wiring diagrams didn't show a neutral/ground bond.

I ohmed out the case ground stud to the neutral on the output and it was open. So should I bond the ground and neutral at the main distribution/breaker box (standalone, isolated system in a shed for a 240v well pump)?

That particular inverter has a neutral flaw regarding input and output. You can't leave them tied together as you would with any other sine wave inverter. They supposedly are working on a fix for it, but I haven't heard if they've corrected it yet.

In your case where there is no existing grid input it should not be an issue. Ground the neutral output or not because if all it is running is a 240 VAC pump the neutral is not involved. Definitely ground the inverter case.

Double and triple check this with Schneider due to the issue I mentioned.

gkar · August 2014

Re: inverter grounding question

Good info, thanks....I shot an email off to Schneider this morning about this already, I'm not holding my breath that they'll answer. Would have been nice to know before I bought this inverter from Northern Arizona Wind and Sun (I wouldn't have).

If I want to add a 120vac outlet and a light to the shed would that flaw affect me being able to do that?

Cariboocoot · August 2014

Re: inverter grounding question

gkar wrote: »

Good info, thanks....I shot an email off to Schneider this morning about this already, I'm not holding my breath that they'll answer. Would have been nice to know before I bought this inverter from Northern Arizona Wind and Sun (I wouldn't have).

If I want to add a 120vac outlet and a light to the shed would that flaw affect me being able to do that?

Good question.
Technically 120 VAC does not require neutral to be grounded; it is done for safety reasons.

I found the thread describing the problem and it appears to be for stacked SW's:
http://forum.solar-electric.com/showthread.php?21344-Fried-conext-sw4024&highlight=Conext+SW

However, I don't trust it to be problem-free for single unit applications.

If anything I would ground the neutral output and leave the DC negative ungrounded (not unusual in systems with DC GFCI), as well as making sure any AC input has floating Neutral.

It's a pity they can write an instruction manual that makes wiring these things clear.

gkar · August 2014

Re: inverter grounding question

Thanks again. Maybe Schneider will provide some info on this. I'll post it up if they contact me. As a side note, all the diagrams included with the inverter were systems that had generators/line in. They all had floating neutrals.

gkar · August 2014

Re: inverter grounding question

Here's what they sent me....

Hello,

Just to clarify with you, are you using our AC/DC switch with your CSW install? the install manual clear shows that the ground and neutral, (PDF page 72/ print out section 3-6)

.I am also required to ask for your contact information
Contact Name:
Contact Email:
Contact Phone:
Mobile Phone:
Address:

vtmaps · August 2014

Re: inverter grounding question

Cariboocoot wrote: »

If anything I would ground the neutral output and leave the DC negative ungrounded (not unusual in systems with DC GFCI), as well as making sure any AC input has floating Neutral.

Huh? In systems with a DC GFCI, the GFCI is the bond. Of course, if any current flows through the "bond" it becomes unbonded.

--vtMaps

Cariboocoot · August 2014

Re: inverter grounding question

vtmaps wrote: »

Huh? In systems with a DC GFCI, the GFCI is the bond. Of course, if any current flows through the "bond" it becomes unbonded.

--vtMaps

No it isn't.
With DC GFI negative is not bonded to ground the way it is in a standard system.
Negative is connected to ground through a low Amperage breaker. If positive becomes connected to ground current flow through this breaker and trips it and the 'main' breakers which are ganged to it thus disconnecting the positive. Negative remains 'slightly' bonded to ground through a resistor.

That is not a negative to ground bond, it is a connection.

gkar · August 2014

Re: inverter grounding question

Schneider replied regarding neutral/ground bonds on my no generator/no grid input type system regarding the Schneider Electric Conext SW 2524 2,500
Watts, 24VDC Inverter/Charger for Split-phase 120/240 VAC:

From Schneider:

"Please see the attached install manual for the CSW unit.

https://schneider-electric.box.com/s/nemnvdgym7xdtigl9wbi

(please see section 3-4 Single-Inverter System (Off-Grid/Backup) Wiring)

Sorry for the incomplete answer, but to answer you question there should be a Neutral-to-Ground Bond in the AC distribution panel."

Thanks to all who attempted to answer this inquiry on this site. Kudos to Schneider for answering the inquiry.

Longboat · August 2014

Re: inverter grounding question

Hello All,
I've already posted once in an older thread - I too have a new Schneider Conext SW inverter - the SW4024. The wiring diagrams are somewhat contradictory - there is no mention of "switching" neutrals in either the manual or guide - and I read with concern the "flaw" mentioned on the 2524. I also purchased the pre-wired AC switchgear (which omitted the AC output neutral line in the pre-installed wiring).
My questions:
Is there a similar "flaw" on the SW4024? What impact does that have on the inverter's operation, safety, and subsequent wiring?
Does the SW4024 switch the neutral internally - thus no output line is necessary?
Is the SW4024 neutral bonded to ground inside the inverter? Or should I make that single connection at the service panel?
All help is very much appreciated.
Longboat

Longboat · August 2014

Re: inverter grounding question

Also, my system is/will be connected to AC input, 120/240 from my outboard Onan 3500 generator, which is also connected to my well pump and backup solar inverter/PV system.
I've already done substantial mounting and wiring of the new inverter - and I am very distressed to read about this "flaw". How long has this been common knowledge, and if it is in fact a manufacturing defect, how can these inverters continue to be sold. I purchased it - along with the AC and DC switchgear within the last 30 days - from NAWS… very concerned, to say the least.
Once again, thank you,
Longboat

gkar · August 2014

Re: inverter grounding question

Longboat wrote: »

Also, my system is/will be connected to AC input, 120/240 from my outboard Onan 3500 generator, which is also connected to my well pump and backup solar inverter/PV system.
I've already done substantial mounting and wiring of the new inverter - and I am very distressed to read about this "flaw". How long has this been common knowledge, and if it is in fact a manufacturing defect, how can these inverters continue to be sold. I purchased it - along with the AC and DC switchgear within the last 30 days - from NAWS… very concerned, to say the least.
Once again, thank you,
Longboat

Sorry I can't answer that question. I haven't even got to the wiring yet, just mounting and research. Do what I did and contact them via their website. Their manuals and wiring diagrams left me with questions that they did eventually answer. Mine was a more simplistic system and question however. From what I've seen in their diagrams with external AC in (generators or grid) the neutrals were isolated from ground which led to my questions. I didn't see anything about "switching" neutrals, just separate bus bars for neutrals and grounds.

Cariboocoot · August 2014

Re: inverter grounding question

The flaw, which may be present in all the new Conext designs for all we know, is that input neutral must not be connected to output neutral. Apparently there is a shunt on one side for measuring current and if the IN and OUT are connected this shunt is bypassed and the inverter can not regulate properly so it goes up in smoke. I am extrapolating here from what has been reported. I haven't handle one and I certainly didn't design it.

As such you have a wiring dilemma which can be compounded by the neutral-ground bond placement. It appears (and again I haven't sorted one out in person) that neutral and ground on the input must be kept separate from each other and input neutral from the output neutral with the one and only N-G bond on the output side.

This would limit wiring options in many cases, such as using it as a UPS for household critical circuits where there is a main service panel with N-G bond on the input side and all neutrals are shared without concern.

The worst part about it is that obviously the wiring requirements, whatever they actually may be, are not made clear in the manual.

Longboat · August 2014

Re: inverter grounding question

Cariboocoot wrote: »

The flaw, which may be present in all the new Conext designs for all we know, is that input neutral must not be connected to output neutral. Apparently there is a shunt on one side for measuring current and if the IN and OUT are connected this shunt is bypassed and the inverter can not regulate properly so it goes up in smoke. I am extrapolating here from what has been reported. I haven't handle one and I certainly didn't design it.

As such you have a wiring dilemma which can be compounded by the neutral-ground bond placement. It appears (and again I haven't sorted one out in person) that neutral and ground on the input must be kept separate from each other and input neutral from the output neutral with the one and only N-G bond on the output side.

This would limit wiring options in many cases, such as using it as a UPS for household critical circuits where there is a main service panel with N-G bond on the input side and all neutrals are shared without concern.

The worst part about it is that obviously the wiring requirements, whatever they actually may be, are not made clear in the manual.

Thread: Schneider Conext Systems have dangerous flaw

I would respectfully request that the Moderator start a new thread including these references to call attention to this manufacturing "flaw". This is a critical safety concern – not to mention a liability issue – from my reading on these forums it would appear that multiple SW inverters have "gone up in smoke" - and I have yet to see any coherent response from Schneider.. The manuals (both installation and owners guide) are very careful to omit any clear reference to neutral routing – and the neutral wiring schematics are unclear and inconsistent at best.

Attempting to navigate the Schneider website is very difficult and there appears to be no direct telephone support line. Perhaps someone on these boards has more direct contact with Schneider, and can get them to respond appropriately.

My primary reason in purchasing the Conext system was its theoretical compatibility and the simplicity of wiring the various components. At this point, I find the system to be anything but that.

Any further help would be much appreciated,
Longboat

Longboat · August 2014

Re: inverter grounding question

By the way, the Schneider SW installation manual clearly shows the single inverter system wiring with neutrals connected for both input and output on a single busbar in the AC switchgear.

Longboat

gkar · August 2014

Re: inverter grounding question

Hey Longboat, try this number and extension. It was in the reply email from Schneider support:

888-778-2733 ext. 45123

re.techsupport@schneider-electric.com is their email

DrDnizzy · September 2017

Hey all, I am having trouble charging my 2013 Nissan leaf from my pure sine inverter. The 24VDC inverter is pulling from a 24V battery bank. The PV system and the battery bank setup is not grounded. I am getting a ground fault reading (blinking green light). After reading some forums, I tried to provide a ground-neutral bond between the AC output of the inverter and the 120V charger. The car indicated it was charging but it did not. The inverter read only 43W output and then read a fault (red light) shortly after. How do I properly ground the system to get the charger to work right? Thoughts?

BB. · September 2017

Have you measured the voltage at the AC outlet? Hot to Neutral=120 vac, Hot to ground=120 vac, Neutral to ground ~ 0 volts? Is the AC outlet a GFI type?

How many watts is the AC inverter? Howe large (AH) is the battery bank? How many Watts is the Leaf charger?

-Bill

PS, continue discussion in DrDnizzy's other thread.

http://forum.solar-electric.com/discussion/352533/off-grid-ev-charging-from-inverter-grounding-issues#latest

inverter grounding question

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