Line side or load side?

Status
Not open for further replies.

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I have a utility guy who insists that a PV connection through a backfed breaker in an MDP which has no main breaker would be a load side interconnection and governed by 705.12 because it is on the load side of the busbar. I asked him for a code reference that establishes that, but he immediately turned it around on me and asked for a code reference that shows that it isn't. Is this too obvious for even the NEC to explicitly state, or is everything I know wrong?
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Seems to me there is no difference between a line side PV connection, and a separate service dedicated to the PV, which is load side connected to that separate service.

So in that sense, the true difference between a line side and load side PV connection would be this: the downstream most (farthest from the utility) point at which a conductor may carry both power produced by the PV inverters and power to other loads (not necessarily simultaneously), is that point a service conductor? Or is it behind some service disconnect not dedicated to the PV system?

I'm curious why the utility guy is involved?

Also, more broadly, I'd say that for any grid-tied PV installation, if you look at the current path from the PV inverters to the service conductors, 705.11 applies after the last (closet to grid) breaker, which is a service disconnect. And 705.12 applies to everything before (away from the grid) of that breaker.

Cheers, Wayne
 
Last edited:

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Seems to me there is no difference between a line side PV connection, and a separate service dedicated to the PV, which is load side connected to that separate service.

So in that sense, the true difference between a line side and load side PV connection would be this: the downstream most (farthest from the utility) point at which a conductor may carry both power produced by the PV inverters and power to other loads (not necessarily simultaneously), is that point a service conductor? Or is it behind some service disconnect not dedicated to the PV system?

I'm curious why the utility guy is involved?

Also, more broadly, I'd say that for any grid-tied PV installation, if you look at the current path from the PV inverters to the service conductors, 705.11 applies after the last (closet to grid) breaker, which is a service disconnect. And 705.12 applies to everything before (away from the grid) of that breaker.

Cheers, Wayne
The utility guy is involved because every commercial PV system we build in that utility's jurisdiction passes across his desk for approval. The issue is what and what is not a supply side interconnection; his contention is that any interconnection to an MDP is a load side (705.12) interconnection irrespective of the presence or absence of a main breaker. Mine is that if there is no main breaker it is a supply side (705.11) connection, since if there is no MCB, all the load breakers in the panel are service disconnects. Whether it is a separate service or not isn't the issue, nor is whether or not the utility will allow such an interconnection.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
The utility guy is involved because every commercial PV system we build in that utility's jurisdiction passes across his desk for approval. The issue is what and what is not a supply side interconnection; his contention is that any interconnection to an MDP is a load side (705.12) interconnection irrespective of the presence or absence of a main breaker. Mine is that if there is no main breaker it is a supply side (705.11) connection, since if there is no MCB, all the load breakers in the panel are service disconnects. Whether it is a separate service or not isn't the issue, nor is whether or not the utility will allow such an interconnection.
Just to be clear, the situation to which I am referring is one where there is no MCB in the MDP and neither is there a disconnecting means between the MDP and the utility revenue meter.
 
Just to be clear, the situation to which I am referring is one where there is no MCB in the MDP and neither is there a disconnecting means between the MDP and the utility revenue meter.
I tended to always think of what you describe as a line side connection. But, consider this:. What if you took this MLO breaker, and that fed a combiner panel board (which is often the case). What is preventing you from calling the mlo breaker just a regular service disconnect? What if you add a few general loads into that combiner panel does that then reinforce an argument for the mlo breaker being just a regular service disconnect because it's not serving only pv?
 
Doesn't a combiner panel essentially turn it into a load side connection? Wouldn't a true supply side connection only exist with a single inverter where the inverter output breaker is also the supply side connection breaker?
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
The utility guy is involved because every commercial PV system we build in that utility's jurisdiction passes across his desk for approval.
I guess I meant what difference does it make (line side vs load side) as far as whatever the utility guy is reviewing. Just curious.

With an MLO panelboard, the panelboard bus are service conductors. If the utility guy wants to treat that install differently from a gutter with splices to multiple breakers, with each breaker in a separate enclosure, then he's mistaken, as far as the physics. Perhaps drawing them both out and showing the equivalence of the connectivity graphs would help him?

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
705.11 and/or 705.12 (depending on code cycle) have always clearly refered to the supply or load side of 'the service disconnecting means'. That should be a slam dunk. There ain't no disconnecting means on the supply side of that busbar. (Which makes the busbars service conductors, btw.)

(Honestly I don't think the last few posts of discussion were required.)
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Doesn't a combiner panel essentially turn it into a load side connection? Wouldn't a true supply side connection only exist with a single inverter where the inverter output breaker is also the supply side connection breaker?
That sort of question is why I like the idea of (a) calling the PV disconnect on a line side connection a service disconnect and then (b) saying that 705.11 applies on the grid side of the service disconnect, and 705.12 applies on the other side of the service disconnect. Those sections may need some wording adjustment for that.

Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
705.11 and/or 705.12 (depending on code cycle) have always clearly referred to the supply or load side of 'the service disconnecting means'.
705.11 uses the phrase "connected on the supply side of the service disconnecting means" which is part of the problem. Which service disconnecting means, if there are more than one? And what about the PV disconnect? If you treat it as a service disconnecting means in the classic line-side connection scenario, then 705.11 would never apply. So it's also tied up in the whole "how do you do bonding in the line side connected PV disconnect?" issue.

705.12 is clearer, it refers to the case the PV is "connected to the load side of the service disconnecting means of the other source(s)". Although it really should be "a" service disconnecting means, as there may be more than one.

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
705.11 uses the phrase "connected on the supply side of the service disconnecting means" which is part of the problem. ...
No, it's crystal clear with respect to the original question. The busbar can't be on the load side of 'the' service disconnecting means or 'a' service disconnecting means if it isn't on the load side any disconnecting means whatsoever.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
The busbar can't be on the load side of 'the' service disconnecting means or 'a' service disconnecting means if it isn't on the load side any disconnecting means whatsoever.
Certainly agreed on the above, the busbars would be service conductors. But that doesn't really address 705.11 vs 705.12.

The more I think about it, I would say that both 705.11 and 705.12 apply to any electric power production source that is grid connected. For a classic load-side connection on a service with a single service disconnecting means, 705.11 is automatically satisfied. But if the service has more than one service disconnecting means for loads, with the power production source interconnected downstream of one of them, you still need to pay attention to 705.11.

Likewise, as electrofelon pointed out, the only classic line-side connection for which 705.12 compliance would be automatic would be a single inverter installation, where the output goes directly to the PV disconnect. An installation with multiple inverters would be subject to the requirements of 705.12.

So getting back to the OP, this gets to why the utility cares about these details, what if any requirements they are imposing that depend on this (to me) false dichotomy of 705.11 vs 705.12.

Cheers, Wayne
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Just to be clear, the situation to which I am referring is one where there is no MCB in the MDP and neither is there a disconnecting means between the MDP and the utility revenue meter.
From my utility POV, if there isn’t an MCB between the meter and the PV connection, it is a line side connection.
I can’t simply go into your whatever and flip a breaker off to kill all the PV.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
705.11 and/or 705.12 (depending on code cycle) have always clearly referred to the supply or load side of 'the service disconnecting means'. That should be a slam dunk. There ain't no disconnecting means on the supply side of that busbar. (Which makes the busbars service conductors, btw.)

(Honestly I don't think the last few posts of discussion were required.)
Agreed on both points. The guy was trying to tell me that 705.12(B)(3)(3) (the 100% rule for the sum of load and supply breakers) was why he wouldn't allow a backfed breaker in the panel. He is the AHJ and can allow or deny whatever he thinks is compliant or not, but none of 705.12 applies. I pointed that out and that's when he insisted that it would be a load side connection.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
First, my understanding on this point has always matched ggunn's, electrofelon's, and jaggedben's. However, as devil's advocate for the moment, I'm not sure that the AHJ here is wrong, given the NEC as written. Parsing the beginning of (2020) 705.12 line by line, the interpretation goes like this (and so others can comment on whether any of the points are rebuttable):

- 705.12 Load-Side Source Connections. The output of an interconnected electric power source shall be permitted to be connected to the load side of the service disconnecting means of the other source(s) at any distribution equipment on the premises.

The PV breaker in the MLO service panel can be considered a service disconnecting means. Then the interconnected electric power source is in fact connected on the load side of that service disconnecting means. The term "distribution equipment" is general and includes service equipment.

And actually I don't think this point matters at all, as I don't see anything limiting the scope of the rest of 705.12 to configurations where the permission in the first sentence is used. So I think just the next point matters:

- Where distribution equipment or feeders are fed simultaneously by a primary source of electricity and one or more other power source and are capable of supplying multiple branch circuits or feeders, or both, the interconnecting equipment shall comply with 705.12(A) through (E).

The MLO service panel is distribution equipment and is fed simultaneously by two sources. So its busbar much comply with 705.12(B)(3).

Cheers, Wayne
 
First, my understanding on this point has always matched ggunn's, electrofelon's, and jaggedben's. However, as devil's advocate for the moment, I'm not sure that the AHJ here is wrong, given the NEC as written. Parsing the beginning of (2020) 705.12 line by line, the interpretation goes like this (and so others can comment on whether any of the points are rebuttable):

- 705.12 Load-Side Source Connections. The output of an interconnected electric power source shall be permitted to be connected to the load side of the service disconnecting means of the other source(s) at any distribution equipment on the premises.

The PV breaker in the MLO service panel can be considered a service disconnecting means. Then the interconnected electric power source is in fact connected on the load side of that service disconnecting means. The term "distribution equipment" is general and includes service equipment.

And actually I don't think this point matters at all, as I don't see anything limiting the scope of the rest of 705.12 to configurations where the permission in the first sentence is used. So I think just the next point matters:

- Where distribution equipment or feeders are fed simultaneously by a primary source of electricity and one or more other power source and are capable of supplying multiple branch circuits or feeders, or both, the interconnecting equipment shall comply with 705.12(A) through (E).

The MLO service panel is distribution equipment and is fed simultaneously by two sources. So its busbar much comply with 705.12(B)(3).

Cheers, Wayne
I think you sum up what is always been somewhat of a point of confusion for me. I think most systems we call supply-side connected are not really a supply-side connection (again that would be pretty much only if there was one inverter). Perhaps the best way to reconcile that is to think of there being "load side rules" and" line side rules", and understand that even a load side connected system can have components subject line side rules.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
First, my understanding on this point has always matched ggunn's, electrofelon's, and jaggedben's. However, as devil's advocate for the moment, I'm not sure that the AHJ here is wrong, given the NEC as written. Parsing the beginning of (2020) 705.12 line by line, the interpretation goes like this (and so others can comment on whether any of the points are rebuttable):

- 705.12 Load-Side Source Connections. The output of an interconnected electric power source shall be permitted to be connected to the load side of the service disconnecting means of the other source(s) at any distribution equipment on the premises.

The PV breaker in the MLO service panel can be considered a service disconnecting means. Then the interconnected electric power source is in fact connected on the load side of that service disconnecting means. The term "distribution equipment" is general and includes service equipment.

And actually I don't think this point matters at all, as I don't see anything limiting the scope of the rest of 705.12 to configurations where the permission in the first sentence is used. So I think just the next point matters:

- Where distribution equipment or feeders are fed simultaneously by a primary source of electricity and one or more other power source and are capable of supplying multiple branch circuits or feeders, or both, the interconnecting equipment shall comply with 705.12(A) through (E).

The MLO service panel is distribution equipment and is fed simultaneously by two sources. So its busbar much comply with 705.12(B)(3).

Cheers, Wayne
You're overconfusing it. The AHJ is wrong.

'Disconnecting means' is defined in Article 100 and a busbar cannot be construed by a reasonable person as a 'device' that qualifies. Only busbars on the load side of the service disconnecting means are subject to the load side rules in 705.12 (formerly 705.12(B) or (D)).
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Agreed on both points. The guy was trying to tell me that 705.12(B)(3)(3) (the 100% rule for the sum of load and supply breakers) was why he wouldn't allow a backfed breaker in the panel. He is the AHJ and can allow or deny whatever he thinks is compliant or not, but none of 705.12 applies. I pointed that out and that's when he insisted that it would be a load side connection.
Yup. He's the AHJ but he's wrong. Or he's wrong but he's the AHJ. Pick your point of view.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Only busbars on the load side of the service disconnecting means are subject to the load side rules in 705.12 (formerly 705.12(B) or (D)).
That is the assumption we have all been making, but I don't believe the actual text of (2020) 705.12 supports that.

The second sentence of 705.12 starts off "Where distribution equipment or feeders are fed simultaneously by a primary source of electricity and one or more other power source . . ." An MLO service panel clearly meets that description, so as written, 705.12 applies to it.

Please rebut, I would prefer to be wrong.

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
That is the assumption we have all been making, but I don't believe the actual text of (2020) 705.12 supports that.

The second sentence of 705.12 starts off "Where distribution equipment or feeders are fed simultaneously by a primary source of electricity and one or more other power source . . ." An MLO service panel clearly meets that description, so as written, 705.12 applies to it.

Please rebut, I would prefer to be wrong.

Cheers, Wayne
The section title and the preceding sentence both reference load side. You don't get to take that sentence out of context.
 
Status
Not open for further replies.
Top