Can I use a common ground wire for three inverters?

[Peter Evans]

Here's the setup. Three high-end 10kw inverters each running independent circuits from mains. They are side by side and I want to daisy chain the
A/C ground wire from inverter to inverter, then use a single ground wire to the grounding stake. I cannot see how this creates a ground loop between each inverter and they share the same ground rod as the mains so there is not one there. I originally planned to use one ground wire from each inverter to ground, but if I put them through one hole they are touching right next to the three inverters anyway so that makes no sense to use three.


Question: Is there any problem sharing the grounds in series between the inverters?

 

[David Castor]

Assuming these three independent circuits are in separate conduits, each one has to have its own equipment grounding conductor. The term "ground wire" is generic and could refer to several different conductors serving different purposes.

 

[Peter Evans]

Thanks. As described each would be grounded in series via the one ground wire serving the singular purpose of grounding.

So: Is there any problem sharing the grounds in series between the inverters?

 

[petersonra]

I am not sure what you mean by ground stake. That implies to me you are talking about a grounding electrode and the conductor would be a grounding electrode conductor.

There is no reason to have a grounding electrode for a vfd.

What is required is an equipment grounding conductor or egc. This will come in as part of the branch circuit that feeds each vfd and extends to the drive and then to the motor housing. It would also bond to the enclosure the VFD is located in.

As long as you meet the requirements of table 250.122, there is no reason the three incoming egcs cannot be tied together and a single egc passed on to each vfd.

Since you don't seem to understand basic electrical requirements it might be best to hand this project off to a qualified electrician rather than get someone killed.

 

[Peter Evans]

I will restate in Electrical Engineering terms. I have three independent 10 kw solar inverters.

Two outputing three-phase 220 volts A/C and one outputing single phase 220 AC.

Each one powers separate circuits not wired to each other to devices not wired to each other and not connected to mains.

Each has to be grounded similar to the house mains.

The are mounted side-by-side but not interconnected via neutrals or loads.

I need to ground them to the grounding rod that the mains use.

The question what would go wrong if I connected the ground post of one inverter to the ground post of next inverter to the ground post of the next inverter then using a single wire, connect to the ground rod?

Can't really see a way to describe it simpler. Has nothing to do with vfd or egc and has nothing to do with electricians.

 

[petersonra]

You are correct. Normally questions about pv systems would be posted in the photovoltaic forum.

 

[jim dungar]

Yes, it is acceptable to connect a bonding jumper from one device to the next and then finally to a single Equipment Grounding Conductor (EGC). The NEC requires the EGC to be run with the circuit conductors, so each of your inverters should already have this conductor, although it may be the raceway.

In the old days 'daisy chaining', like you are thinking of doing, was discouraged primarily due to the interconnection of the communications cabling shields.

 

[Peter Evans]

Yes, it is acceptable to connect a bonding jumper from one device to the next and then finally to a single Equipment Grounding Conductor (EGC). The NEC requires the EGC to be run with the circuit conductors, so each of your inverters should already have this conductor, although it may be the raceway.

In the old days 'daisy chaining', like you are thinking of doing, was discouraged primarily due to the interconnection of the communications cabling shield

Thanks, terminology notwithstanding, that answers my question. If I understand correctly the main panel is considered to be "Equipment"? It seems to me it would make more sense for that term to be used to things downstream from the supply side. As a follow up, can you imagine any reason the single EGC would need to be a greater size for the three instead of one?

 

[Peter Evans]

Thanks, terminology notwithstanding, that answers my question. As a follow up, can you imagine any reason the single EGC would need to be a greater size for the three instead of one?

Yes, it is acceptable to connect a bonding jumper from one device to the next and then finally to a single Equipment Grounding Conductor (EGC). The NEC requires the EGC to be run with the circuit conductors, so each of your inverters should already have this conductor, although it may be the raceway.

In the old days 'daisy chaining', like you are thinking of doing, was discouraged primarily due to the interconnection of the communications cabling shields.

Thanks, terminology notwithstanding, that answers my question. If I understand correctly each inverter and the main panel are considered to be "Equipment"? It seems to me it would make more sense for that term to be used to things downstream from the supply side.

"The NEC requires the EGC to be run with the circuit conductors, so each of your inverters should already have this conductor, although it may be the raceway."

I have no idea what this means exactly. Each inverter has a neutrals and ground to each subpanel they connect to (4-wire). This ground wire I am talking about is to ground from each inverter. There are separate raceways going to the three separate subpanels than the raceway from the inverter ("mains") ground, how can they be "run with the circuit conductors"?

As a follow up, can you imagine any reason the single EGC would need to be a greater size for the three instead of one?

 

[electrofelon]

I will restate in Electrical Engineering terms. I have three independent 10 kw solar inverters.

Two outputing three-phase 220 volts A/C and one outputing single phase 220 AC.

Each one powers separate circuits not wired to each other to devices not wired to each other and not connected to mains.

Each has to be grounded similar to the house mains.

The are mounted side-by-side but not interconnected via neutrals or loads.

I need to ground them to the grounding rod that the mains use.

The question what would go wrong if I connected the ground post of one inverter to the ground post of next inverter to the ground post of the next inverter then using a single wire, connect to the ground rod?

Can't really see a way to describe it simpler. Has nothing to do with vfd or egc and has nothing to do with electricians.

Out of curiosity, what are these inverters powering? Do they have a grounded conductor? It seems we are talking about a grounding electrode conductor covered by 250.30. IS this a grounded system or not? IF its a grounded system see 250.30(A). IF its an ungrounded system, see 250.30(B). Generally I dont see an issue with doing what you describe assuming the terminals are listed for multiple conductors or you use some sort of connector that is, and the installation complies with 250.64, particularly (E).

 

[electrofelon]

I have no idea what this means exactly. Each inverter has a neutrals and ground to each subpanel they connect to (4-wire). This ground wire I am talking about is to ground from each inverter. There are separate raceways going to the three separate subpanels than the raceway from the inverter ("mains") ground, how can they be "run with the circuit conductors"?

As a follow up, can you imagine any reason the single EGC would need to be a greater size for the three instead of one?

I am still uncertain what you have here. Are these grid tied inverters? I thought you said "they are not connected to mains" and that along with the "220 volts" which let me to believe these are an isolated stand alone electrical system, but Im not so sure now.

 

[Peter Evans]

I am still uncertain what you have here. Are these grid tied inverters? I thought you said "they are not connected to mains" and that along with the "220 volts" which let me to believe these are an isolated stand alone electrical system, but Im not so sure now.

Thanks for the reply. Each inverter is simply powering four separate circuits entirely independent of the house mains for eventual elimination of the house mains entirely. Each inverter is autonomous from the others in all ways. Each has their own internal circuit breaker and each needs to be grounded to earth. The question is: Is there any problem with using a daisy-chaining the ground posts together, then using a single wire to the grounding pole. So it is four separate power supplies independent of each other. The inverters are grid-tied type but will never be connected in this way. It makes no sense to me to supply the power company inverter equipment, replacement, and maintenance for a few cents per Kwh.

I am guessing this is not often done so that is the source of the confusion. You can think of it as I have four houses, three powered only by inverters and one powered only by mains and I want to tie the three houses with inverters grounds together, then to a single wire that goes to the fourth houses grounding rod. Except that the three houses with inverters have the inverters two feet apart and the grounding pole is 25 feet away at the house with the mains.

 

[electrofelon]

Thanks for the reply. Each inverter is simply powering four separate circuits entirely independent of the house mains for eventual elimination of the house mains entirely. Each inverter is autonomous from the others in all ways. Each has their own internal circuit breaker and each needs to be grounded to earth. The question is: Is there any problem with using a daisy-chaining the ground posts together, then using a single wire to the grounding pole. So it is four separate power supplies independent of each other. The inverters are grid-tied type but will never be connected in this way. It makes no sense to me to supply the power company inverter equipment, replacement, and maintenance for a few cents per Kwh.

I am guessing this is not often done so that is the source of the confusion. You can think of it as I have four houses, three powered only by inverters and one powered only by mains and I want to tie the three houses with inverters grounds together, then to a single wire that goes to the fourth houses grounding rod. Except that the three houses with inverters have the inverters two feet apart and the grounding pole is 25 feet away at the house with the mains.

Can you provide the make and model of the inverters? They may not suitable for supplying a building.

 

[Peter Evans]

Not related to the grounding issue, but they are 10kw whole-house inverters all with the capacity to grid-tie, thought that won't be happening.

 

[electrofelon]

Not related to the grounding issue, but they are 10kw whole-house inverters all with the capacity to grid-tie, thought that won't be happening.

model #? I cant provide much more of an answer than provided in post #10 without knowing specifics of the inverter.

 

[jim dungar]

Terminology is extremely important. The word ground is ambiguous and should not be used without an adjective.

Very basically:
All sources must have a grounding electrode conductor. Effectively this is the connection to the 'ground rod'.
All metallic surfaces must be bonded together. This may be a green insulated conductor or a metallic conduit.

Two different but related concepts. It looks like you want to bond the equipment but questions have been raised concerning your grounding electrode system

 

[jaggedben]

...

Question: Is there any problem sharing the grounds in series between the inverters?

Thanks for the reply. Each inverter is simply powering four separate circuits entirely independent of the house mains for eventual elimination of the house mains entirely. Each inverter is autonomous from the others in all ways. Each has their own internal circuit breaker and each needs to be grounded to earth. The question is: Is there any problem with using a daisy-chaining the ground posts together, then using a single wire to the grounding pole. ...

Like electrofelon I'm really curious about these inverters but taking what you say above as given I'll answer the question.

What you are describing is multiple separately derived systems. Daisy-chaining the grounds between the inverters sounds to me like a violation of 250.64(C) and 250.30(6)(c)(3), which require a common grounding electrode conductor to be continuous. The code compliant way to do it would be to tap the common grounding electrode conductor to each inverter as described in 250.30(6).

 

[jaggedben]

Consider that you probably want to ground them in such a way that if you have to remove any inverter for some reason, it should not affect the system grounding for any of the others.

 

[electrofelon]

Consider that you probably want to ground them in such a way that if you have to remove any inverter for some reason, it should not affect the system grounding for any of the others.

The system grounding and if it exists is my big concern/question. These systems are required to be grounded per 250.20. In "grid tie mode" which these supposedly have, there would not be a system bonding jumper, where in "off grid mode" there would need to be a SBJ. Not sure if there is something that needs to be done physically or in programming, but it could be dangerous if not done correctly.

 

[Peter Evans]

Terminology is extremely important. The word ground is ambiguous and should not be used without an adjective.

Very basically:
All sources must have a grounding electrode conductor. Effectively this is the connection to the 'ground rod'.
All metallic surfaces must be bonded together. This may be a green insulated conductor or a metallic conduit.

Two different but related concepts. It looks like you want to bond the equipment but questions have been raised concerning your grounding electrode systemI a

The system grounding and if it exists is my big concern/question. These systems are required to be grounded per 250.20. In "grid tie mode" which these supposedly have, there would not be a system bonding jumper, where in "off grid mode" there would need to be a SBJ. Not sure if there is something that needs to be done physically or in programming, but it could be dangerous if not done correctly.

Terminology is extremely important. The word ground is ambiguous and should not be used without an adjective.

Very basically:
All sources must have a grounding electrode conductor. Effectively this is the connection to the 'ground rod'.
All metallic surfaces must be bonded together. This may be a green insulated conductor or a metallic conduit.

Two different but related concepts. It looks like you want to bond the equipment but questions have been raised concerning your grounding electrode systemOh

Terminology is extremely important. The word ground is ambiguous and should not be used without an adjective.

Very basically:
All sources must have a grounding electrode conductor. Effectively this is the connection to the 'ground rod'.
All metallic surfaces must be bonded together. This may be a green insulated conductor or a metallic conduit.

Two different but related concepts. It looks like you want to bond the equipment but questions have been raised concerning your grounding electrode system

I agree, applicable terminology is applicable but you cannot ground without an electrode or a conductor so those are extraneous and obfuscate the meaning. I thought I must be thinking about this all wrong because my original post seemed precise and inviolate. But after three attempts I am getting questions about the brand of the inverter, lol. So I showed the OP to my 14 year old daughter who knows nothing about any of this and she understood immediately. The issue seems to be the system for teaching the understanding of relatively simple questions creates an inability to comprehend that she has not been educated out of...yet.