MLO Panel as a service.

Status
Not open for further replies.

SolarPro

Senior Member
Location
Austin, TX
Good point. :blink: Okay, then, per 705.2:

Power production equipment. The generating source, and all distribution equipment associated with it, that generates electricity from a source other than a utility supplied service.

This is relevant exercise because PV system designs are trending away from centralized architectures. Besides the increasing use of ac modules and microinverter systems, 3-phase string inverters are displacing centralized inverters.
 

Smart $

Esteemed Member
Location
Ohio
But IMHO the inclusion of "suitable for interconnection to a utilization load" actually muddies the issue.
...
To me this actually has the opposite result to what you propose. :)
To whom are you responding?

In response to JB, SP, and yourself, I simply ask any of you to cite one or more reference (NEC) which supports a PV system as a power source beyond the utility-interactive inverter output OCPD.

JB is correct that the Point of Connection may not be limited to one point... but I believe that is only true for multiple inverters, not each individual inverter.

I have no problem with SP's statement regarding an inverter accumulation (or aggregation) panel, as long it is MLO. If it is MCB, you thus have two OCPD's between each inverter and service conductor for what he considers a supply-side connection. Code wording does not support this conclusion.

All in all, the problem I see is PV professionals perceive all their work as the PV system, regardless of its configuration. My experience and dealings with the NEC and its interpretation is IMO much more diverse.... which in turn allows me to see issues which PV professionals do not. I see this as the reason why there is so much confusion in interpreting Articles 690 and 705.12... and also the reason why these Articles keep getting what seems to be major revisions each cycle.
 

Smart $

Esteemed Member
Location
Ohio
Good point. :blink: Okay, then, per 705.2:

Power production equipment. The generating source, and all distribution equipment associated with it, that generates electricity from a source other than a utility supplied service.

This is relevant exercise because PV system designs are trending away from centralized architectures. Besides the increasing use of ac modules and microinverter systems, 3-phase string inverters are displacing centralized inverters.
How does that clear up anything? IMO that just muddles the issue even more by using the term distribution equipment.

705.12 said:
(D) Utility-Interactive Inverters. The output of a utility-
interactive inverter shall be permitted to be connected tothe load side of the service disconnecting means of the
other source(s) at any distribution equipment on the premises.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
...
JB is correct that the Point of Connection may not be limited to one point... but I believe that is only true for multiple inverters, not each individual inverter.

I don't believe the number of inverters makes a difference to the general point.

It's interesting that while 705 has a definition (a vague one, IMO) for "Point of Common Coupling", it makes no use of this phrase in the rest of the article. So much for the practical importance of that concept.

It's also noteworthy that it defines the "Inverter output circuit" as going back to the 'service equipment.' This corroborates that rules for interconnected power sources extend beyond the first OCPD connected to an inverter. Definitions aside, that's important and justified for physical reasons.

All in all, the problem I see is PV professionals perceive all their work as the PV system, regardless of its configuration. My experience and dealings with the NEC and its interpretation is IMO much more diverse.... which in turn allows me to see issues which PV professionals do not. I see this as the reason why there is so much confusion in interpreting Articles 690 and 705.12... and also the reason why these Articles keep getting what seems to be major revisions each cycle.

I think there's much more being worked out than a mere social struggle between PV professionals vs. everyone else. It's really because a) systems that the Code always assumed were moving power in only one direction may now be moving power in multiple directions, and b) the technology and the number of people using it are changing rapidly.

How does that clear up anything? IMO that just muddles the issue even more by using the term distribution equipment.

What are we trying to clear up? If we are trying to clear up where the inverter output circuit ends, I think we should not try too hard to do that. The energy from the inverter output could theoretically travel miles away on the utility distribution network. I think the reason the NEC definition stops at the service equipment is that that's essentially where the scope of the NEC stops. (Or at any rate, I think that's a sensible reason for the definition to stay that way.)
 

Smart $

Esteemed Member
Location
Ohio
I don't believe the number of inverters makes a difference to the general point.
It doesn't if they all utilize the same Point of Connection.

It's interesting that while 705 has a definition (a vague one, IMO) for "Point of Common Coupling", it makes no use of this phrase in the rest of the article. So much for the practical importance of that concept.
The term has been removed from the 2014 edition.

It's also noteworthy that it defines the "Inverter output circuit" as going back to the 'service equipment.' This corroborates that rules for interconnected power sources extend beyond the first OCPD connected to an inverter. Definitions aside, that's important and justified for physical reasons.
Exactly. It's necessary for interaction of dual/multiple systems... but that does not extend the PV system as a power source... i.e. the PV System ends at each inverter OCPD (which serves as a disconnecing means), same as a service ends at the service disconnecting means (which has integral or immediately adjacent OCPD).

I think there's much more being worked out than a mere social struggle between PV professionals vs. everyone else. It's really because a) systems that the Code always assumed were moving power in only one direction may now be moving power in multiple directions, and b) the technology and the number of people using it are changing rapidly.
Your entitled to your opinion...

What are we trying to clear up? If we are trying to clear up where the inverter output circuit ends, I think we should not try too hard to do that. The energy from the inverter output could theoretically travel miles away on the utility distribution network. I think the reason the NEC definition stops at the service equipment is that that's essentially where the scope of the NEC stops. (Or at any rate, I think that's a sensible reason for the definition to stay that way.)
You continue to side-step the issue at the heart of it. Narrow the focus down to power source conductors and non-power-source conductors (e.g. the equivalent to service conductors vs. feeders, but for PV conductors vs. feeders)....

Where there is no feeder conductor between inverter output and service conductor, you have a supply-side connection. Otherwise, it is a load-side connection.
 
Last edited:

SolarPro

Senior Member
Location
Austin, TX
I have no problem with SP's statement regarding an inverter accumulation (or aggregation) panel, as long it is MLO. If it is MCB, you thus have two OCPD's between each inverter and service conductor for what he considers a supply-side connection. Code wording does not support this conclusion.

Code wording also does not support the use of a MCB in an inverter accumulation panel. :slaphead: You seem attached to this scenario, but why put an OCPD where it can't do anything useful? The OCP goes at the potential source of overcurrent, which is downstream, toward the utility.

There's no reason 1 MW PV system consisting entirely of ac modules or string inverters couldn't be supply side connected. (It sounds like you are saying that isn't the case, but maybe I'm misunderstanding you.) Doing so would require a considerable ac collection system, with may levels of circuit breakers. But it's all part of the accumulation system for the on-site variable energy resource. You'll have "one switch w/ OCP to rule them all," and the POI is located on the utility side of that switch. The ac accumulation system is part of the interconnected electric power production source.

Like jaggedben, I think the solar industry vs. electricians angle completely misses what's going on. PV systems were the second largest source of new generation in the US in 2013. Utilities are the solar industry's biggest customer. These systems may not yet be in the mainstream of the electrical or utility industries, but they are definitely designed and installed by mainstream electrical engineering and construction companies. There aren't enough solar bozos to support the growth that the industry has seen recently, not to mention the increase in project capacity. The fact of the matter is that there'd be a lot more underemployed electricians and EEs, if not for the booming solar industry.

Those EEs and electricians who are riding that wave are hip to which way the current is flowing. (See first paragraph.)
 

Smart $

Esteemed Member
Location
Ohio
Code wording also does not support the use of a MCB in an inverter accumulation panel. :slaphead: You seem attached to this scenario, but why put an OCPD where it can't do anything useful? The OCP goes at the potential source of overcurrent, which is downstream, toward the utility.

There's no reason 1 MW PV system consisting entirely of ac modules or string inverters couldn't be supply side connected. (It sounds like you are saying that isn't the case, but maybe I'm misunderstanding you.) Doing so would require a considerable ac collection system, with may levels of circuit breakers. But it's all part of the accumulation system for the on-site variable energy resource. You'll have "one switch w/ OCP to rule them all," and the POI is located on the utility side of that switch. The ac accumulation system is part of the interconnected electric power production source.

Like jaggedben, I think the solar industry vs. electricians angle completely misses what's going on. PV systems were the second largest source of new generation in the US in 2013. Utilities are the solar industry's biggest customer. These systems may not yet be in the mainstream of the electrical or utility industries, but they are definitely designed and installed by mainstream electrical engineering and construction companies. There aren't enough solar bozos to support the growth that the industry has seen recently, not to mention the increase in project capacity. The fact of the matter is that there'd be a lot more underemployed electricians and EEs, if not for the booming solar industry.

Those EEs and electricians who are riding that wave are hip to which way the current is flowing. (See first paragraph.)
Aside from what I consider mostly superfluous to the issue, I agree.


Let me state the issue another way, since it seems you are hell bent on referring to which way the current can and does flow...

Where, with respect to a conductor and its splices or taps, power can compliantly be utilized by a premises load (including any yet to exist load), the conductor is neither a service conductor nor a PV System conductor.... i.e., if the conductor supplies a premises load, or can be spliced or tapped to supply such a load.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
You continue to side-step the issue at the heart of it. Narrow the focus down to power source conductors and non-power-source conductors (e.g. the equivalent to service conductors vs. feeders, but for PV conductors vs. feeders)....

Where there is no feeder conductor between inverter output and service conductor, you have a supply-side connection. Otherwise, it is a load-side connection.

I still don't agree with the last part, in principle or in details. The type of connection is defined by where it is, regardless of how many there are. Also, a load side connection can be in a MCB service panel, with no feeder.

You may think I'm side stepping the issue, but I think I'm disagreeing that your issue is relevant or usefully defined.

Where, with respect to a conductor and its splices or taps, power can compliantly be utilized by a premises load (including any yet to exist load), the conductor is neither a service conductor nor a PV System conductor.... i.e., if the conductor supplies a premises load, or can be spliced or tapped to supply such a load.

First, let's stay away from the term 'PV System conductor' (which to me implies DC). We are talking about 'Inverter Output Circuits' in this thread, which are defined. Again, a feeder that meets your definition can still be part of an Inverter Output Circuit; the two uses are not mutually exclusive. And it is certainly the case that such a feeder can be subject to the rules in 705.

If there's a sticky issue, maybe it's whether the 'Inverter Output' is part of the 'PV system.' But I don't think that actually affects the clarity of which 705 rules apply to certain types/sections of inverter output circuits, which was the original subject of this thread (to which we are now barely hanging on). Those sections are written clearly enough to not be affected by that issue. Maybe some other sections of the code still need clarity on the issue (disconnect requirements in 690, for example), but I don't see what it has to do with what's been discussed in this thread already.
 

Smart $

Esteemed Member
Location
Ohio
I still don't agree with the last part, in principle or in details. The type of connection is defined by where it is, regardless of how many there are.
And I agree with your second sentence. What's lacking is agreement in what defines where this/these connection(s) is/are.

FWIW, 690.17(A) of the 2014 edition expands on the possible disconnecting means to permit a listed "...PV molded-case circuit breaker marked for use in PV systems". If using such breakers for the inverter output, I'd be willing to cede that more than one breaker can exist between inverter output and service conductor and still be a supply-side connection.

Also, a load side connection can be in a MCB service panel, with no feeder.
In this case, the feeder is the panel bus. While it is not a feeder conductor of the wire type usually associated with the term feeder, the panel bus is a circuit conductor which does fall under the definition of a feeder.
Feeder. All circuit conductors between the service equipment,
the source of a separately derived system, or other
power supply source and the final branch-circuit overcurrent
device.
Which brings up another issue that many misinterpret... The service equipment of an MCB service panel ends at the MCB. The rest of the panel, including the bus, is not service equipment.

You may think I'm side stepping the issue, but I think I'm disagreeing that your issue is relevant or usefully defined.
What we deem it as is irrelevant, as it amounts to what it is either way... :D

First, let's stay away from the term 'PV System conductor' (which to me implies DC). We are talking about 'Inverter Output Circuits' in this thread, which are defined.
Let's not. What it implies to you is also irrelevant. You should know by now we are talking about the AC output(s) of a Solar Photovoltaic (PV) System as indicated by the title of Article 690. But if it helps the discussion, I'll try to refrain from using the term... :p

Again, a feeder that meets your definition can still be part of an Inverter Output Circuit; the two uses are not mutually exclusive. And it is certainly the case that such a feeder can be subject to the rules in 705.
I believe you misunderstand. What I am calling a feeder is any circuit conductor which is neither a power supply source or branch circuit conductor... period. It is a feeder by definition, no matter how much you attempt to construe meanings by the use of various terms, whether defined or implied.

If there's a sticky issue, maybe it's whether the 'Inverter Output' is part of the 'PV system.'
Quite likely you are correct in a sense. Article 690 does not clarify whether the inverter output circuit ends at its disconnecting means or OCPD. I'm well aware the output extends beyond the disconnecting means and OCPD. What I am trying to distinguish is the PV System ends at the inverter output OCPD and no longer under the scope of Article 690, just like a service ends at the service equipment and no longer under the scope of Article 230.

But I don't think that actually affects the clarity of which 705 rules apply to certain types/sections of inverter output circuits, which was the original subject of this thread (to which we are now barely hanging on). Those sections are written clearly enough to not be affected by that issue. Maybe some other sections of the code still need clarity on the issue (disconnect requirements in 690, for example), but I don't see what it has to do with what's been discussed in this thread already.
No response necessary here after the replies I have provided above... :happyno:
 
Last edited:

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
What I am calling a feeder is any circuit conductor which is neither a power supply source or branch circuit conductor... period. It is a feeder by definition, no matter how much you attempt to construe meanings by the use of various terms, whether defined or implied.

I'm not disputing whether any feeder is a feeder. But there is nothing in the code that says that a conductor cannot be both a feeder and part of an inverter output circuit. In fact, the definitions logically entail that some conductors must be.

Article 690 does not clarify whether the inverter output circuit ends at its disconnecting means or OCPD.

Article 705 clarifies that it ends at the service equipment (at least if the only other source is a utility).
 
Last edited:
In this case, the feeder is the panel bus. While it is not a feeder conductor of the wire type usually associated with the term feeder, the panel bus is a circuit conductor which does fall under the definition of a feeder.

Feeder. All circuit conductors between the service equipment,
the source of a separately derived system, or other
power supply source and the final branch-circuit overcurrent
device.

Which brings up another issue that many misinterpret... The service equipment of an MCB service panel ends at the MCB. The rest of the panel, including the bus, is not service equipment.

We had a very similar discussion recently. All I will say is I dont think what you say is a slam dunk - while there is wording implying that the actual MCB is the only component of the service equipment, there is multitude of other wording that implies it has a broader scope than that.
 

Smart $

Esteemed Member
Location
Ohio
I'm not disputing whether any feeder is a feeder. But there is nothing in the code that says that a conductor cannot be both a feeder and part of an inverter output circuit. In fact, the definitions logically entail that some conductors must be.

Article 705 clarifies that it ends at the service equipment (at least if the only other source is a utility).
And for the time being, I will not contest that. What I continue to try and distinguish is where the scope of Article 690 ends, Article 705 carries the implications of an inverter's output back to the service conductor, which includes all wire- and bus-type conductors... and getting back to the issue at hand, means that if you have two or more OCPD's between inverter and service conductor, you have a load-side connection under Article 705, which automatically assumes this/these conductor(s) is/are bus or feeder conductor(s). Article 690 is out of the picture.

Item (6) under 230.82 permits connecting solar photovoltaic systems to the supply side of the service disconnecting means. If Article 690 is out of the picture for the in-between conductor(s) described earlier, then you are not connecting a Solar photovoltaic system to the OCPD at the service conductor... confirmation it is not a supply-side connection.
 

Smart $

Esteemed Member
Location
Ohio
We had a very similar discussion recently. All I will say is I dont think what you say is a slam dunk - while there is wording implying that the actual MCB is the only component of the service equipment, there is multitude of other wording that implies it has a broader scope than that.
You must offer more than a passing comment to join this discussion.... :D
 

hurk27

Senior Member
Just a quick note, I notice everyone has been calling this a service panel, and or supply side connection but the OP in post one clearly stated it is being fed from a meter main combo which means the service disconnect is at the meter, not sure if that will through a wrench into the party but thought I would just point this small detail out.

Unless I'm not understanding what the OP is saying in post 1? if the meter has the main service breaker then this breaker is what protects this panel, the post 1 is confusing.


I'm trying to figure out a way to hook 4.5kW (30A OCPD required) of solar to a house that is using a MLO as a service panel. The panel has 2 breakers on it, one 50A breaker for the A/C and a 100A for a subpanel. Since this is a MLO panel I'm wondering how it is protected. Is it the size of the feeders coming from the meter? (Its a meter/main combo.)
 
Last edited:

Smart $

Esteemed Member
Location
Ohio
Just a quick note, I notice everyone has been calling this a service panel, and or supply side connection but the OP in post one clearly stated it is being fed from a meter main combo which means the service disconnect is at the meter, not sure if that will through a wrench into the party but thought I would just point this small detail out.

Unless I'm not understanding what the OP is saying in post 1? if the meter has the main service breaker then this breaker is what protects this panel, the post 1 is confusing.
Hmmm... possibly.

I was of the impression he has a meter/panel combo, e.g.:

http://w3.usa.siemens.com/us/SiteCo...net/Products/2008-04-16_2/MC0606L1200RJBA.pdf
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Backing away from the issue itself a little...

What this points out to me is that the code surrounding PV is not yet written well enough. Anything that is a commonly encountered situation should be addressed by succinct language that unambiguously addresses it. Arguments like this one should be moot and how you wire up a system should not hinge upon what you call a piece of gear.

Good luck with that one, right? :D
 
Status
Not open for further replies.
Top