250.24(C) Grounded Conductor Brought to Service Equipment

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am1954

Member
Location
NY
Occupation
contractor
I’m having trouble interpreting requirements of the neutral (both the location and the sizing) for Enphase IQ series systems with line side connections.

As per the Enphase manual, no neutral is required (or provided) from the inverters, so there is obviously no neutral from the roof to the point where those branch circuits terminate.

But 250.24(C) says “the grounded conductor(s) shall be routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure”

I’m confused by the words “each service disconnecting means” as opposed to just saying “each service disconnect”. Does this mean we only have to bring the neutral to the service disconnect (ie the fused disco prior to the point of POI) and it can terminate there? Or does it mean it needs to continue on to any additional AC disconnects in the system (ie a rapid shutdown initiation device, a dedicated combo panel for Enphase branch circuits, etc)? I realize that the Envoy requires a neutral, but if no Envoy was involved, I’m unclear what the code is requiring.

And in terms of sizing the neutral, do we just use the minimum acceptable size as per 250.102(C)(1), based on the largest conductor in the PV system? or is there somewhere else we should be looking for sizing?

Finally, if the ungrounded conductors are tapped in the MSP, would you also tap the grounded (neutral) conductor or just land it on the neutral bar in the MSP?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I'm gathering that you are doing a supply side connection for the PV system, even though you didn't state that explicitly. If that is not the case then forget about all this, because it's only relevant to supply side connections.

There have been a lot of threads about this, the most recent one is here:

The neutral (grounded conductor) is required by 250.24(C) because that is the ground fault return path to the source. If you are on the 2020 NEC it is explicit that you follow it (see 250.25). On previous code cycles it is somewhat vague if you can or are required to bring a green wire instead of a white one to bond the disconnect. So ask your AHJ. But really that's about all we are talking about, the color of the wire that is bonded to the disconnect.

Does this mean we only have to bring the neutral to the service disconnect (ie the fused disco prior to the point of POI) and it can terminate there?

Yes.
(If your AHJ agrees with bringing it that far.)
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
And in terms of sizing the neutral, do we just use the minimum acceptable size as per 250.102(C)(1), based on the largest conductor in the PV system? or is there somewhere else we should be looking for sizing?

Correct table. It's based on the size of ungrounded conductor you bring from the tap to the disconnect.
Finally, if the ungrounded conductors are tapped in the MSP, would you also tap the grounded (neutral) conductor or just land it on the neutral bar in the MSP?
Doesn't matter as long as it's all in the same enclosure. If you tapped in a separate box you would tap all conductors there.
 

BradPV

Member
Location
North Carolina
Occupation
Residential PV Qualifier
I’m confused by the words “each service disconnecting means” as opposed to just saying “each service disconnect”. Does this mean we only have to bring the neutral to the service disconnect (ie the fused disco prior to the point of POI) and it can terminate there? Or does it mean it needs to continue on to any additional AC disconnects in the system (ie a rapid shutdown initiation device, a dedicated combo panel for Enphase branch circuits, etc)? I realize that the Envoy requires a neutral, but if no Envoy was involved, I’m unclear what the code is requiring.
The service disconnect is defined in article 100 and is the first disconnecting means from the utility, this means the service equipment is only in one location for each individual service ( supply/line side tap creates a new service).
Finally, if the ungrounded conductors are tapped in the MSP, would you also tap the grounded (neutral) conductor or just land it on the neutral bar in the MSP?
Yes, in my opinion the neutral should be tapped (when possible) so that the new neutral ground bond takes place in the new service disconnect. Although the example drawings shown by NC show the neutral tapping on the bus. jaggedben is correct it really doesn't matter, it is just a consistency thing for me.
 

am1954

Member
Location
NY
Occupation
contractor
Yes, in my opinion the neutral should be tapped (when possible) so that the new neutral ground bond takes place in the new service disconnect. Although the example drawings shown by NC show the neutral tapping on the bus. jaggedben is correct it really doesn't matter, it is just a consistency thing for me.
Lets say the neutral is not tapped, but is just brought to the bus bar in the MSP (in our particular situation there are physical space restraints that would make tapping the neutral difficult). In this situation, would you still bond N and G in the service disconnect? Or would bonding it in the service disco create a second NG bond for that service (considering the NG bond in the MSP the first NG bond).
 

BradPV

Member
Location
North Carolina
Occupation
Residential PV Qualifier
Lets say the neutral is not tapped, but is just brought to the bus bar in the MSP (in our particular situation there are physical space restraints that would make tapping the neutral difficult). In this situation, would you still bond N and G in the service disconnect? Or would bonding it in the service disco create a second NG bond for that service (considering the NG bond in the MSP the first NG bond).
This is a subject that goes around often so I will give you my opinion....A new service requires the neutral ground bond at the first means of disconnect. I like to see the N/G bond in the AC disco even if we land on the bus in the meter disco. I am attaching the approved drawings from the NCOSFM that oversees the code interpretation here.
 

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  • Temporarily Approved Solar Photovoltaic Electrical Schematics.pdf
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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Lets say the neutral is not tapped, but is just brought to the bus bar in the MSP (in our particular situation there are physical space restraints that would make tapping the neutral difficult). In this situation, would you still bond N and G in the service disconnect? Or would bonding it in the service disco create a second NG bond for that service (considering the NG bond in the MSP the first NG bond).
In the 2020 NEC 250.25 requires you to bring the neutral to the new disconnect and bond it there with an MBJ. Since you do this, you don't need to run a green wire also. The code has allowed multiple MBJs where there are multiple service disconnects for a very long time, so this is not considered to create objectionable current per se. It remains vauge whether the PV disconnect is officially a service disconnect or not, but 250.25 requires you to treat it like one for bonding and grounding.

In previous codes the question was inadequately addressed, and people either did as described above, or they ran a green wire from the MSP to the new disco and did not bond neutral to ground there.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
In the 2020 NEC 250.25 requires you to bring the neutral to the new disconnect and bond it there with an MBJ. Since you do this, you don't need to run a green wire also. The code has allowed multiple MBJs where there are multiple service disconnects for a very long time, so this is not considered to create objectionable current per se. It remains vauge whether the PV disconnect is officially a service disconnect or not, but 250.25 requires you to treat it like one for bonding and grounding.

In previous codes the question was inadequately addressed, and people either did as described above, or they ran a green wire from the MSP to the new disco and did not bond neutral to ground there.
But by all means verify this with the AHJ. There are multiple AHJs here in Texas that do not consider a line side PV connection to be a service even though they have adopted the 2020 NEC. They require an EGC all the way to the PV system and no N-G bond in the disco.
 

BradPV

Member
Location
North Carolina
Occupation
Residential PV Qualifier
In the 2020 NEC 250.25 requires you to bring the neutral to the new disconnect and bond it there with an MBJ. Since you do this, you don't need to run a green wire also. The code has allowed multiple MBJs where there are multiple service disconnects for a very long time, so this is not considered to create objectionable current per se. It remains vauge whether the PV disconnect is officially a service disconnect or not, but 250.25 requires you to treat it like one for bonding and grounding.

In previous codes the question was inadequately addressed, and people either did as described above, or they ran a green wire from the MSP to the new disco and did not bond neutral to ground there.
The NEC defines a service disconnect as being supplied from the utility. A supply side tap is directly fed from the POCO as there is no disco ahead of it.
 

BradPV

Member
Location
North Carolina
Occupation
Residential PV Qualifier
But by all means verify this with the AHJ. There are multiple AHJs here in Texas that do not consider a line side PV connection to be a service even though they have adopted the 2020 NEC. They require an EGC all the way to the PV system and no N-G bond in the disco.
But agreed, check with the AHJ....
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
The NEC defines a service disconnect as being supplied from the utility. A supply side tap is directly fed from the POCO as there is no disco ahead of it.
Actually the NEC never has never used the word 'supply', but its definition used to be the center of the argument against calling a PV disconnect a service disconnect.

2017 and earlier definition:
The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.

Since PV conductors were primarily for sending energy the other way, it was argued the PV disconnect was not a service disconnect.

2020 definition:
The conductors and equipment connecting the serving utility to the wiring system of the premises served.

So your argument works better if the 2020 NEC applies. However, language involving 'on the supply side of the service disconnecting means' still muddies the waters, so 250.25 clears up grounding and bonding regardless (hopefully).
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
But by all means verify this with the AHJ. There are multiple AHJs here in Texas that do not consider a line side PV connection to be a service even though they have adopted the 2020 NEC. They require an EGC all the way to the PV system and no N-G bond in the disco.
Sure, but if they are on the 2020 NEC it no longer hinges so much on what they call a service disconnect as it does on whether they follow or ignore/ammend/delete 250.25.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Both definitions mention the term "serving utility." A stand-alone solar-based system would involve no service, nor use that term.

Thus, it seems to me that the addition of a solar system to a service would not make any of the new parts service equipment.

But, then, you have been exposed to my particular flavor of logic before. "Not always right, but never in doubt." :giggle:
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Both definitions mention the term "serving utility." A stand-alone solar-based system would involve no service, nor use that term.

Thus, it seems to me that the addition of a solar system to a service would not make any of the new parts service equipment.

But, then, you have been exposed to my particular flavor of logic before. "Not always right, but never in doubt." :giggle:
First, we are not talking about stand alone systems. Second, if the connection is made on the load side of the service disconnect then yes, you'd be right. But in the case where the connection is made on the utility side of the exisiting service disconnect, then the question arises.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
But in the case where the connection is made on the utility side of the exisiting service disconnect, then the question arises.
Is the new connection supplying a new load? (I have no direct experience with solar.)

Do the service conductors branch off as if one was adding another service disconnect?

Does it effectively become another service panel, and be drawn as such in a one-line?

If yes, then I might be inclined to agree that it should be wired as such, with bonding.

For a system with the connection made after the main, like a sub-panel, then no bond.


Please tell me whether I am at least grasping the gist of the conversation. :unsure:
 

BradPV

Member
Location
North Carolina
Occupation
Residential PV Qualifier
Actually the NEC never has never used the word 'supply', but its definition used to be the center of the argument against calling a PV disconnect a service disconnect.
You are correct for the service definition, it does call it the "serving utility". But in reference to the taps as called out in 705.11 (2020) and 705.12 (2017) the do call it a "supply side tap".

It is still ONE service. What it creates is another set of service entrance conductors.
It is still one service drop but according to the definition of a service "The conductors and equipment connecting the serving utility to the wiring system of the premises served." it is one drop serving two pieces of service equipment both of which are their own disconnect from the utility. In other words if you open the service disconnect from the structure will the solar service still be energized? That is where my argument is based. And I will say again, this is my opinion of an article that has been the base of quite a few discussions on this and many other forums and the AHJ's have a varied and differing opinion often as well.
 

BradPV

Member
Location
North Carolina
Occupation
Residential PV Qualifier
Is the new connection supplying a new load? (I have no direct experience with solar.)
While solar is indeed arguably not a load it is considered a load in the NEC. The inverter needs to draw AC power before it will invert the DC and it always needs control power even at night.
Do the service conductors branch off as if one was adding another service disconnect?
If tapped prior to the 1st means of disconnect then they are still service conductors no matter the size of the conductor.
Does it effectively become another service panel, and be drawn as such in a one-line?
Yes it is and does.
For a system with the connection made after the main, like a sub-panel, then no bond.
Agreed. I have been specifically speaking (typing) to a tap on the serving/supply side of the utility.
Please tell me whether I am at least grasping the gist of the conversation. :unsure:
I think you have it sir.
But, then, you have been exposed to my particular flavor of logic before. "Not always right, but never in doubt." :giggle:
I wish I had thought of that line :D
 
It is still one service drop but according to the definition of a service "The conductors and equipment connecting the serving utility to the wiring system of the premises served." it is one drop serving two pieces of service equipment both of which are their own disconnect from the utility. In other words if you open the service disconnect from the structure will the solar service still be energized?
I never said there can't be multiple pieces of service equipment, and multiple disconnects. But 99.8% of the time these together will still be one service. We can discuss whether the PV disconnect is wired "like" a service, i.e. neutral bonded, but that doesn't make it another service.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Sure, but if they are on the 2020 NEC it no longer hinges so much on what they call a service disconnect as it does on whether they follow or ignore/ammend/delete 250.25.
I disagree that the NEC is clear and concise on this issue, but at the end of the day it really doesn't matter what you and I think. The AHJ has the final say and it doesn't matter, either, whether they are right or wrong. If designing systems the way they direct me to were to result in an unsafe or malfunctioning condition, then I might go to the mat over it, but it doesn't.
 
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