Commercial solar PV grounding with CT cabinet supply side connection

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solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
I am designing a 186kW PV system and need to make the grid connection on the supply side, and am using a CT cabinet. I would like some advice on grounding. The existing 480V service has an 800A fused main disconnect before the MLO panelboard. The Neutral and ground bond is in the main disconnect, as is the GEC. I have an AC combiner taking the three 62kW inverter outputs and providing a single PV System output to a 400A nonfused disconnect to serve as the PV System disconnect. I am bringing the system gound from the inverters thru to the ground bus in the combiner, and then then on to ground lug in System disconnect, and to the building main disconnect ground / neutral bus. I am unsure if the CT cabinet needs a separate ground or if just bonding the neutral to the ground in the CT Cabinet is what is required. I see example utility connection diagrams with the Netral bonded to the ground lug in the CT cabinet. Attached is the diagram. Is there anything wrong I am doing here? Explanations and/or code references would be appreciated.

solarken
 

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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I don't think that there is anything glaringly 'wrong', but don't make any assumptions about what the AHJ's opinion is or should be. This is more or less another thread on whether 'the PV disconnect a service disconnect or not', which if you search through past threads you will find has been an intractable discussion here. The NEC has been quite vague on this stuff, although I believe the 2020 NEC will generally require and endorse what you've drawn, perhaps not to every last detail. The general alternative to what you've drawn would be to treat the PV disconnect as another service disconnect, and to have a main bonding jumper there and send an additional GEC from there to the existing grounding electrode system. In other words it would be mirror image of the existing service disconnect and you would not need a green wire running from one to the other. Either way, you have an effective ground fault path, either through the green wire in what you've drawn, or through the white wire if you do it the other way. You're AHJ, however, may think that for some reason it really matters which method you use.

The only question/quibble I have with your drawing is that the ground symbol in the PV AC combiner should not represent an electrode. If that just represents the equipment ground terminal bar then it's fine.
 

pv_n00b

Senior Member
Location
CA, USA
As jaggedben wrote, some of this depends on how you treat the PV AC disconnect. Some AHJs require a system ground and some don't allow it. Outside of that the CT cabinet needs to be bonded to the rest of the grounded equipment with an EGC. The way it is drawn it is floating out there with no EGC. It will look like the EGC is duplicating the neutral connection to the building disconnect but there needs to be an EGC and a neutral even though they are technically in parallel.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I don't think that there is anything glaringly 'wrong', but don't make any assumptions about what the AHJ's opinion is or should be. This is more or less another thread on whether 'the PV disconnect a service disconnect or not', which if you search through past threads you will find has been an intractable discussion here.

I wouldn't call it intractable; under present code it's compliant to do it either way. Ask the AHJ and do like they say.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
As jaggedben wrote, some of this depends on how you treat the PV AC disconnect. Some AHJs require a system ground and some don't allow it. Outside of that the CT cabinet needs to be bonded to the rest of the grounded equipment with an EGC. The way it is drawn it is floating out there with no EGC. It will look like the EGC is duplicating the neutral connection to the building disconnect but there needs to be an EGC and a neutral even though they are technically in parallel.

I see the CT cabinet bonded to the neutral, as required for stuff on the supply side of the service disconnect. I also see an EGC or supply side bonding jumper brought from the service disconnect over to the PV disconnect. I think that's essentially okay, in context of other comments above.
 

solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
I see the CT cabinet bonded to the neutral, as required for stuff on the supply side of the service disconnect. I also see an EGC or supply side bonding jumper brought from the service disconnect over to the PV disconnect. I think that's essentially okay, in context of other comments above.

I just received the 2020 NEC version and was hoping it would provide some clarification on this, but not sure it does. I am now thinking I should remove the Neutral to Ground bonding jumper in the CT cabinet and run an EGC from the CT cabinet to the Main Disconnect that has the GEC and the main bonding jumper installed.

Can you provide the NEC secionts that specify that the CT cabinet must have the neutral bonded to it's ground becuase it is on the supply side of the service disconnect? I provided the original dwgs to the AHJ and he is reviewing the permit application now, but have not yet received feedback from him on this.

Thanks for the help.
 

solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
As jaggedben wrote, some of this depends on how you treat the PV AC disconnect. Some AHJs require a system ground and some don't allow it. Outside of that the CT cabinet needs to be bonded to the rest of the grounded equipment with an EGC. The way it is drawn it is floating out there with no EGC. It will look like the EGC is duplicating the neutral connection to the building disconnect but there needs to be an EGC and a neutral even though they are technically in parallel.

I am tending to agree with you now, I think I need to remove the bonding jumper in the CT cabinet and run an EGC from CT cabinet to the building disconnect.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I didn't say those things, and I don't think you should do that if it represents the existing installation. The code section that supports bonding the CT cabinet to the neutral is 250.92.

I just got my 2020 NEC the other day as well, and they removed the proposed section on bonding and grounding that would have clarified this stuff.
 

solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
I didn't say those things, and I don't think you should do that if it represents the existing installation. The code section that supports bonding the CT cabinet to the neutral is 250.92.

I just got my 2020 NEC the other day as well, and they removed the proposed section on bonding and grounding that would have clarified this stuff.

Can you clarify what you mean by "I don't think you should do that if it represents the existing installation"?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I mean that if that bond already exists, I wouldn't remove it. If the CT cabinet isn't properly bonded now, there might be a more convenient way to bond it with a supply side jumper from somewhere else, or maybe bonding to the neutral in the cabinet would still be the best way.
 
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solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
I mean that if that bond already exists, I wouldn't remove it. If the CT cabinet isn't properly bonded now, there might be a more convenient way to bond it with a supply side jumper from somewhere else, or maybe bonding to the neutral in the cabinet would still be the best way.

I'm sorry, I might not have been clear. I am adding the CT Cabinet, it does not exist currently. The current service comes in from the utility transformer into the main building 800A fused disconnect. The load side of the disconnect goes to the panelboard main lugs. I am inserting a new CT cabinet between the utility transformer and the existing main 800A disconnect, to provide the extra lugs I need to land the solar on the supply side, and also to provide a convenient place to measure the current and voltage for the grid energy meter. As I add the CT cabinet, one of my questions was should I bond the neutral to the CT cabinet? There is already a Neutral to Equipment Ground main bonding jumper in the existing Main Disconnect.
 
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I'm sorry, I might not have been clear. I am adding the CT Cabinet, it does not exist currently. The current service comes in from the utility transformer into the main building 800A fused disconnect. The load side of the disconnect goes to the panelboard main lugs. I am inserting a new CT cabinet between the utility transformer and the existing main 800A disconnect, to provide the extra lugs I need to land the solar on the supply side, and also to provide a convenient place to measure the current and voltage for the grid energy meter. As I add the CT cabinet, one of my questions was should I bond the neutral to the CT cabinet? There is already a Neutral to Ground main bonding jumper in the existing Main Disconnect.

Yes. Bonding between the service point and the service disconnect is done with the grounded conductor. You also have the choice of bonding it by running a bonding jumper to hit the grounded conductor somewhere else, such as the service disconnect. Usually CT cabs have a convenient way to bond the neutral buss to the cabinet.
 

solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
Yes. Bonding between the service point and the service disconnect is done with the grounded conductor. You also have the choice of bonding it by running a bonding jumper to hit the grounded conductor somewhere else, such as the service disconnect. Usually CT cabs have a convenient way to bond the neutral buss to the cabinet.

I ended up removing the CT cabinet from the design altogether, and replacing the service conductors between the utility and the main disconnect with heavier wire and one fewer parallel conductors, to free up a lug on the line side of the main disconnect for landing the solar. While moot for this project, I still would like to understand for future projects, If there is already a main bonding jumper in the main service disconnect to achieve the neutral to ground bond just like typical in all building services, and you come along and add solar, using a CT cabinet to provide the additional lugs for a line side tap, and inserted between the existing main disconnect and the utility, should the neutral in the CT cabinet also be bonded to the CT cabinet/ground as well? Specifically, there is already the main bonding jumper in the existing main disconnect, would adding a CT cabinet with a main bonding jumper installed there as well, so that there are two points where neutral is bonded to ground (in the main disconnect, and in the CT cabinet) violate any NEC requirement? Or should the bonding jumper be omitted from the added CT cabinet? The examples I have found for CT cabinet wiring have all been from utility side perspectives, where they owned the CT cabinet and it was out near the utility transformer, not on the customer premises, and they show the neutral to ground bond. In my case, I would have installed the Ct cabinet as customer-premise equipment, with no EGC between the CT cabinet and the utility-owned equipment. Thanks.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I ended up removing the CT cabinet from the design altogether, and replacing the service conductors between the utility and the main disconnect with heavier wire and one fewer parallel conductors, to free up a lug on the line side of the main disconnect for landing the solar. While moot for this project, I still would like to understand for future projects, If there is already a main bonding jumper in the main service disconnect to achieve the neutral to ground bond just like typical in all building services, and you come along and add solar, using a CT cabinet to provide the additional lugs for a line side tap, and inserted between the existing main disconnect and the utility, should the neutral in the CT cabinet also be bonded to the CT cabinet/ground as well? Specifically, there is already the main bonding jumper in the existing main disconnect, would adding a CT cabinet with a main bonding jumper installed there as well, so that there are two points where neutral is bonded to ground (in the main disconnect, and in the CT cabinet) violate any NEC requirement? Or should the bonding jumper be omitted from the added CT cabinet? The examples I have found for CT cabinet wiring have all been from utility side perspectives, where they owned the CT cabinet and it was out near the utility transformer, not on the customer premises, and they show the neutral to ground bond. In my case, I would have installed the Ct cabinet as customer-premise equipment, with no EGC between the CT cabinet and the utility-owned equipment. Thanks.

As of now there are two ways to do it and usually the AHJ decides which they prefer. You can treat the line side connection as a separate service, where you bond N to G in the PV disco, any enclosures between the disco and the service conductors are bonded to N, and there is no EGC back to the service from the PV AC disco but an external bond between G on the PV side and building G, i.e., the way CPS in San Antonio wants it. Or you can treat it like any other PV interconnection, where you do not bond N to G in the PV disco and there is an EGC all the way back to the service, i.e., the way most of the other AHJ's in Texas want it.

I was told that the 2020 NEC would take a stand on the issue and direct it to be one way or the other, but rumor has it (I have not yet seen a copy of the 2020 NEC) that the committee writing that section of the code has backed away from it.
 
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