connecting EGC and neutral for a line side tap (supply side connection)

iwire

Moderator
Staff member
Location
Massachusetts
If words don't matter, then why do you even have an opinion (post #31) as to whether it should be called a service disconnect?
I did not say 'words don't matter',

I said you could call it power or energy it does not change what the switch is actually doing.


Power and energy are different things and the definition of a service refers to one of them and not the other, and supply side PV disconnect does connect one of them and not the other.
Again, IMO not relevant to the discussion.



You're going to have to explain what you mean by that, because toi me in all safety respects the PV disconnect is exactly like a service disconnect.
I don't have to do anything. :D

But they are not exactly alike, one kills the power/energy/electricity to the building or structure and the other does not.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I've come around to view it pretty much the same way, which is why I didn't propose that change to the service definition last time around.

There is one type of case I've seen where it really does make a difference, and could really suck if you didn't get on the same page as your AHJ before you started install. That's where your (large) inverter doesn't require a neutral. In that case you'd like to argue that the PV disconnect is not a service disconnect so that you don't have to bring a neutral to it according to 250.24(C). Or at least you'd like your AHJ to accept that it's safe regardless of what terms you use. The neutral itself could cost a lot of money if it's large and long, but what would cost more is if you made your conduit too small before asking your AHJ if they would require it.
Which is why I always confer with the AHJ on this issue if they don't have published documents that tell me what they want to see.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
There was a proposal for that very language back in the 2014 cycle. It was unanimously rejected, with the reasoning that it was already covered and the language wasn't necessary. They basically said "Duh, everyone already knows to look in 230". No one needs to learn anything new, just keep doing what we've been doing all along...disconnecting service entrance conductors with service-rated disconnects.
All other things aside, this was obviously an error on their part. If the code were unambiguous on this issue we wouldn't be having this discussion.
 

iwire

Moderator
Staff member
Location
Massachusetts
There was a proposal for that very language back in the 2014 cycle. It was unanimously rejected, with the reasoning that it was already covered and the language wasn't necessary. They basically said "Duh, everyone already knows to look in 230". No one needs to learn anything new, just keep doing what we've been doing all along...disconnecting service entrance conductors with service-rated disconnects.
I do not think you where following me.
 

Carultch

Senior Member
Location
Massachusetts
Please explain how a disconnect for an interactive PV inverter(s) presents any different problems from an additional service disconnect for a permitted load. I would submit that they are no different with respect to any safety principle. The code generally requires bonding the neutral to ground at all service disconnects and does not regard any parallel paths thus created as a problem per se.
Ggunn gave a good example, and exactly what I was thinking. The same problem exists with bonding neutral to ground at service disconnects in general, where there also could be a prevailing imbalance to the loads. Unfortunately, that is what you have to do anyway, regardless of whether it physically makes sense or not.

Like I said, where it really belongs for it to make physical sense, is at the transformer secondary. However it probably didn't make it there in most cases, because the service transformer is seldom in the customer's control or governed by the NEC. So the service disconnect is sort of the next best place. I do not understand why it is required to do this at every single service disconnect (as in, what is the real life consequence in only doing it at one of the disconnects?), but somehow that is the way the code ended up being written.
 

Smart $

Esteemed Member
Location
Ohio
Point. Consider a PV system on a three phase service consisting of three inverters of unequal size connected phase to neutral, interconnected on the supply side. Because of the unbalanced nature of the system there would be current on the neutral, wouldn't there? It seems to me that bonding neutral to ground at the disco would put current on the ground between the disco and the point of interconnection.
Yes, neutral current would be present during nominal production conditions.

There would only be current on both the neutral and ground between disconnect and interconnect if you created a parallel path. See 250.6. Some see the NGB as culprit, but technically, the NGB is only one compliant way of bonding the disconnect and grounding the PV system. If you created a parallel path, you must be using two otherwise compliant methods of bonding the disconnect and grounding the PV system.
 

jaggedben

Senior Member
I said you could call it power or energy it does not change what the switch is actually doing.
It does change it. The switch disconnects power in both directions but energy flow in only one.

But they are not exactly alike, one kills the power/energy/electricity to the building or structure and the other does not.
This is where you are wrong. If the system is interactive then both kill power/energy/electricity to the building or structure. (If there is some kind of backup then the PV disconnect kills power/energy/electricity to the building or structure up to the point of a transfer switch.)
 
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jaggedben

Senior Member
Nobody cherry picking any wording on this end. :huh::blink:
Contrast your diagram showing 'between', as well as my somewhat facetious post #41, with my post #27. The former are what I am calling cherrypicking: focusing on the wording of one particular section, while ignoring the code as a whole.
 

jaggedben

Senior Member
Ggunn gave a good example, and exactly what I was thinking. The same problem exists with bonding neutral to ground at service disconnects in general, where there also could be a prevailing imbalance to the loads. Unfortunately, that is what you have to do anyway, regardless of whether it physically makes sense or not.
As you said in the bolded part. This is allowed and in fact required for any service conductors that are not for PV, and the fact that a connection is to a PV system changes nothing safety wise.

To be clear, I'm somewhat agnostic on the question of whether we need to settle this question about whether a PV disconnect is a service disconnect. (I've moved over time from 'it's a service disconnect' to something like ggunn's position of 'it doesn't matter much as long as you talk to your AHJ'.) But what I'm not agnostic about is saying that there is no interesting safety difference between a PV disconnect and service disconnect.

Like I said, where it really belongs for it to make physical sense, is at the transformer secondary. However it probably didn't make it there in most cases, because the service transformer is seldom in the customer's control or governed by the NEC. So the service disconnect is sort of the next best place. I do not understand why it is required to do this at every single service disconnect (as in, what is the real life consequence in only doing it at one of the disconnects?), but somehow that is the way the code ended up being written.
I'm with you as as far as not fulling understanding where the requirements of Article 230 came from. But if there is a safety reason they ought to be changed, that has nothing to do with supply side PV disconnects as far as I can tell.
 
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I think you will find in upstate NY working through NYSERDA on a supply side connection they want neutral to ground bond on the AC disco. Thus, making your former main panel a sub.
Not true as far as making your main panel a sun I work on long Island some upstate never had to make my main panel a sub

Sent from my SAMSUNG-SM-G900A using Tapatalk
 

wwhitney

Senior Member
Location
Berkeley, CA
Yes, neutral current would be present during nominal production conditions.

There would only be current on both the neutral and ground between disconnect and interconnect if you created a parallel path.
In the situation under discussion, isn't there automatically a parallel path via the GES to the regular service?

Cheers, Wayne
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Yes, neutral current would be present during nominal production conditions.

There would only be current on both the neutral and ground between disconnect and interconnect if you created a parallel path. See 250.6. Some see the NGB as culprit, but technically, the NGB is only one compliant way of bonding the disconnect and grounding the PV system. If you created a parallel path, you must be using two otherwise compliant methods of bonding the disconnect and grounding the PV system.
The way SATX has us do it is to bond N to G in the disco, break the ground from the service at that point, drive a new ground at the disco, and bond the new rod to the service ground. There is a parallel path to the neutral conductor from the NG connection in the disco to the new ground rod and through the connection between the two rods.
 

Smart $

Esteemed Member
Location
Ohio
Contrast your diagram showing 'between', as well as my somewhat facetious post #41, with my post #27. The former are what I am calling cherrypicking: focusing on the wording of one particular section, while ignoring the code as a whole.
Well post #27 is definitely cherry picking... :p
 

Smart $

Esteemed Member
Location
Ohio
In the situation under discussion, isn't there automatically a parallel path via the GES to the regular service?

Cheers, Wayne
Not if you install NGB and don't run an EBJ or a GEC tap, or vice versa. Grounding rules permit, if not "encourage" using the grounded service conductor for bonding. Both an NGB and GEC tap are required if you (or the AHJ) say the disconnect is a service disconnecting means... but 250.6 allows you to revise the connections to eliminate parallel pathways.
 

wwhitney

Senior Member
Location
Berkeley, CA
Not if you install NGB and don't run an EBJ or a GEC tap, or vice versa. Grounding rules permit, if not "encourage" using the grounded service conductor for bonding. Both an NGB and GEC tap are required if you (or the AHJ) say the disconnect is a service disconnecting means... but 250.6 allows you to revise the connections to eliminate parallel pathways.
OK, you're saying use 250.6 to skip any connection to the GES at a line side PV disconnect with NGB. That would avoid the parallel path I mentioned. Since I'm not 100% clear on the real purpose of the GES in the first place, I can't really say where omitting that GES connection has any downside. There would still be a GES connection via the service neutral and the other service.

Cheers, Wayne
 

jaggedben

Senior Member
Well post #27 is definitely cherry picking... :p
Um, post #27 is the opposite of cherry picking. It's a comprehensive look at all the code sections that can be interpreted either way on this question, rather than picking a particular one that supports a certain position.

I wonder if you really don't understand the meaning of cherry picking, or if you're just trying to get my goat. :roll:
 

jaggedben

Senior Member
In the situation under discussion, isn't there automatically a parallel path via the GES to the regular service?

Cheers, Wayne
Notwithstanding the other answers you've received, or other ways of doing it, I believe that is a compliant installation.
 

Smart $

Esteemed Member
Location
Ohio
Um, post #27 is the opposite of cherry picking. It's a comprehensive look at all the code sections that can be interpreted either way on this question, rather than picking a particular one that supports a certain position.

I wonder if you really don't understand the meaning of cherry picking, or if you're just trying to get my goat. :roll:
Not trying to get your goat... at all. Acts of ill will are basically not in my [conscious] nature. I suppose perhaps a little in my primal nature, being human and all. :angel:

You brought up cherry picking and in so much stated you did regarding the "former" in your post. As to that post, "Yes" would be cherry picking for the "Yes" cause, "No" for "No" cause. "Yes" and "No" together would not be cherry picking... but I'm certain I could do some "nit" picking. ;)

BTW, I have physically picked cherries (among other fruits and nuts) from the orchard we had on the farm I grew up on... so I'd say I understand cherry picking better than most. :D
 

iwire

Moderator
Staff member
Location
Massachusetts
It does change it. The switch disconnects power in both directions but energy flow in only one.
It does not matter.

This is where you are wrong. If the system is interactive then both kill power/energy/electricity to the building or structure. (If there is some kind of backup then the PV disconnect kills power/energy/electricity to the building or structure up to the point of a transfer switch.)
We are talking about a line side tap to connect a PV system, opening that switch will not kill power to the building.
 

Smart $

Esteemed Member
Location
Ohio
Notwithstanding the other answers you've received, or other ways of doing it, I believe that is a compliant installation.
Being compliant depends on whether the disconnect is technically a service disconnect or not. If not, it is not compliant. Even when it is a service disconnect, it would not be compliant with 250.6... but it seems all AHJ's ignore 250.6 when it comes to service bonding.
 
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