PV disconnect confusion

[electrofelon]

Up for discussion is the following: What exactly is a "Photovoltaic disconnect" ? I think it depends on the context. Consider a typical supply side connection with a safety switch. Most people would call that the PV disconnect. Many utilities require a "PV disconnect" which could be separate from any NEC disconnects. 690.13 seems to be what we commonly call the "DC disconnect" (usually built in to an inverter) and the "official" Pv disconnect right? Is the 690.13 disconnect what 690.56(B) is referring to? Then we have the disconnects in 690.15 which is, in practice, the "AC disconnect" and the DC disconnect in the inverter. I see lots of inconsistency with this in the field.

Consider the following situation: I have a remote meter pedestal utilizing 230.40 exception #3 with a set of SEC to the house and a second set to a detached structure with a PV system on in. The inverters are on the second floor and have integral DC disconnects and a AC combiner panel next to them. The combiner panel feeder connects load side to the service panel via backfed breaker. There is also a utility required safety switch disconnect on the outside of the building that breaks the feeder to the combiner panel. How would you classify the various disconnects here?

 

[Carultch]

Up for discussion is the following: What exactly is a "Photovoltaic disconnect" ? I think it depends on the context. Consider a typical supply side connection with a safety switch. Most people would call that the PV disconnect. Many utilities require a "PV disconnect" which could be separate from any NEC disconnects. 690.13 seems to be what we commonly call the "DC disconnect" (usually built in to an inverter) and the "official" Pv disconnect right? Is the 690.13 disconnect what 690.56(B) is referring to? Then we have the disconnects in 690.15 which is, in practice, the "AC disconnect" and the DC disconnect in the inverter. I see lots of inconsistency with this in the field.

Consider the following situation: I have a remote meter pedestal utilizing 230.40 exception #3 with a set of SEC to the house and a second set to a detached structure with a PV system on in. The inverters are on the second floor and have integral DC disconnects and a AC combiner panel next to them. The combiner panel feeder connects load side to the service panel via backfed breaker. There is also a utility required safety switch disconnect on the outside of the building that breaks the feeder to the combiner panel. How would you classify the various disconnects here?

I think any disconnect between a PV module (or multiple) and the point of interconnection would be a "photovoltaic disconnect". The point of interconnection being, the point where PV specific equipment connects to general electrical equipment. A point marked as such with a label identifying it as the point of interconnection.

In your situation, the inverter integrated disconnects would be "PV SYSTEM DC DISCONNECT" & "PV SYSTEM AC DISCONNECT" respectively. Or a "PV SYSTEM DUAL AC/DC DISCONNECT" if operated by the same handle. Each breaker in the AC combiner would be a "PV SYSTEM AC DISCONNECT", with a master label covering all within the unit. The utility required disconnect would be a "PV SYSTEM AC DISCONNECT", and any PV-specific switch by the point of interconnection, be it a load-side backfed breaker, or an adjacent fused switch would be a "PV SYSTEM AC DISCONNECT".

 

[SolarPro]

FWIW:

PV system disconnect. In NEC 2017, Section 690.13 clarifies that the PV system disconnect is the disconnecting means that separates the PV system conductors from all other conductors associated with all other electrical systems. In this context, other electrical systems include energy storage systems, multimode inverters, wind systems, load distribution wiring and so forth. The diagrams in Figure 1 and Figure 2 indicate where the PV system disconnect is located in a variety of system configurations and architectures.

Note that the PV system disconnect in these diagrams is not always located at the end of what we traditionally think of as the PV system. On one hand, the PV system disconnect location is relatively self-evident in interactive and ac module systems. The PV system disconnect locations in Figure 1, for example, correspond with what we think of as the end of the PV system. On the other hand, the PV system disconnect location is more obscure in multi-module and stand-alone systems. As the complexity of the electrical power system increases, the PV system disconnect may not be located at what we think of as the end of the electrical system, as shown in Figure 2.

To identify the PV system disconnect in these complex electrical systems, you need to differentiate between conductors associated with different power sources. In dc-coupled multimode and stand-alone systems, for instance, we have traditionally considered the inverter and energy storage components as part of the PV system. Now, separate Code articles cover energy storage systems and PV power systems. This change means that the PV system disconnect is necessarily located upstream from energy storage conductors and equipment, perhaps at a charge-controller circuit breaker or similar. In an ac-coupled multimode system, meanwhile, the PV system disconnect is necessarily located upstream from any utilization load circuits. Here again, the energy storage and multimode inverter components are no longer defined as part of the PV power system.

By more narrowly defining the scope and definition of a PV power system, CMP 4 was able to eliminate the source of much confusion in Article 690 and remove language duplicated in other articles. While the new figures in Section 690.1(B) by no means present an exhaustive treatment of the many possible system permutations, they provide good guidance regarding the PV system disconnect location. Simply put, if you open what you think is the PV system disconnecting means and look toward the PV array, there should be no other conductors or equipment from other electrical systems on the PV side of that disconnect. If conductors and equipment associated with other power sources and electrical systems are upstream, then you are not at the PV system disconnect. Keep moving toward the array until you are at a location where there are clearly no other electrical systems on the array side of the switch.

Source: NEC 2017 Updates for PV System

 

[jaggedben]

For years I've been hoping that the code would better define terms and separate PV (DC) requirements from AC requirements. I don't expect people colloquially to stop referring to AC disconnects as PV disconnects, but I hope it would be clear for those who are code knowledgeable.

Anyway that seems to be largely a pipe dream. It's all muddy to me.

 

[electrofelon]

I think any disconnect between a PV module (or multiple) and the point of interconnection would be a "photovoltaic disconnect". The point of interconnection being, the point where PV specific equipment connects to general electrical equipment. A point marked as such with a label identifying it as the point of interconnection.

In your situation, the inverter integrated disconnects would be "PV SYSTEM DC DISCONNECT" & "PV SYSTEM AC DISCONNECT" respectively. Or a "PV SYSTEM DUAL AC/DC DISCONNECT" if operated by the same handle. Each breaker in the AC combiner would be a "PV SYSTEM AC DISCONNECT", with a master label covering all within the unit. The utility required disconnect would be a "PV SYSTEM AC DISCONNECT", and any PV-specific switch by the point of interconnection, be it a load-side backfed breaker, or an adjacent fused switch would be a "PV SYSTEM AC DISCONNECT".

Thank you all for replies. Before I can digest, I need to ask a couple more questions (hope this doesnt get too confusing with a whole bunch of discussions going on):
1. Do we all agree or not that 690.13 is a DC disconnect?
2. Is the point of interconnection in my example the combiner panel or the main panel? If the main, would adding a general purpose circuit/load to the combiner then make the combiner the point of interconnection?

 

[pv_n00b]

There's never been a "PV Disconnect" as a single piece of equipment defined in the code, that's why there is no common definition. Up through 2014 there were two types of disconnects:

690.13; Building or Other Structure Supplied by a Photovoltaic System. Means shall be provided to disconnect​

all ungrounded dc conductors of a PV system from all other conductors in a building or other structure.​

This is for DC disconnects that isolate the array and would not include any AC disconnect at the POCC.

690.15; Disconnection of Photovoltaic Equipment. Means shall be provided to disconnect equipment, such as inverters, batteries, and charge controllers, from all ungrounded conductors of all sources.
​

This strangely enough applied to both DC and AC disconnects. It also points to the need for disconnects to isolate power to equipment, hence the disconnects that are part of inverters. It still does not specifically identify the PV disconnect at the POCC but that our could be one of the disconnects that isolates equipment.

And then there is the utility specified PV disconnect at the POCC.

In 2017 things were moved around a bit.

690.13 became; Photovoltaic System Disconnecting Means. Means shall be provided to disconnect the PV system from all wiring systems including power systems, energy storage systems, and utilization equipment and its associated premises wiring.​

This removed the DC conductor restriction so it applies to both DC and AC circuits. "PV System" is not defined so good luck drawing a line around that. But if you assume the PV system is all the PV equipment then it seems to be including a single AC disconnect that isolates the PV system from everything else.

690.15 became; Disconnection of Photovoltaic Equipment. Isolating devices shall be provided to isolate PV modules, ac PV modules, fuses, dc-to-dc converters inverters, and charge controllers from all conductors that are not solidly grounded.
​

While the wording changed I think it still says basically the same as the 2014 690.15. The 2014 690.15 gave examples of equipment but did not actually limit it to that specific equipment, where 2017 690.15 seems to be giving a list that it applies to and that it does not apply to anything else. But this is all wordsmithing anyway.

The 2017 690.13(C) is new information, saying that a disconnect on a supply side interconnection has to be service equipment rated.

So where does this all leave us? Still no definition for "PV Disconnect" so pretty much where we were, arguing over what is the PV disconnect. Continue the fun.

 

[electrofelon]

There's never been a "PV Disconnect" as a single piece of equipment defined in the code, that's why there is no common definition. Up through 2014 there were two types of disconnects:

690.13; Building or Other Structure Supplied by a Photovoltaic System. Means shall be provided to disconnect​

all ungrounded dc conductors of a PV system from all other conductors in a building or other structure.​

This is for DC disconnects that isolate the array and would not include any AC disconnect at the POCC.

690.15; Disconnection of Photovoltaic Equipment. Means shall be provided to disconnect equipment, such as inverters, batteries, and charge controllers, from all ungrounded conductors of all sources.
​

This strangely enough applied to both DC and AC disconnects. It also points to the need for disconnects to isolate power to equipment, hence the disconnects that are part of inverters. It still does not specifically identify the PV disconnect at the POCC but that our could be one of the disconnects that isolates equipment.

And then there is the utility specified PV disconnect at the POCC.

In 2017 things were moved around a bit.

690.13 became; Photovoltaic System Disconnecting Means. Means shall be provided to disconnect the PV system from all wiring systems including power systems, energy storage systems, and utilization equipment and its associated premises wiring.​

This removed the DC conductor restriction so it applies to both DC and AC circuits. "PV System" is not defined so good luck drawing a line around that. But if you assume the PV system is all the PV equipment then it seems to be including a single AC disconnect that isolates the PV system from everything else.

690.15 became; Disconnection of Photovoltaic Equipment. Isolating devices shall be provided to isolate PV modules, ac PV modules, fuses, dc-to-dc converters inverters, and charge controllers from all conductors that are not solidly grounded.
​

While the wording changed I think it still says basically the same as the 2014 690.15. The 2014 690.15 gave examples of equipment but did not actually limit it to that specific equipment, where 2017 690.15 seems to be giving a list that it applies to and that it does not apply to anything else. But this is all wordsmithing anyway.

The 2017 690.13(C) is new information, saying that a disconnect on a supply side interconnection has to be service equipment rated.

So where does this all leave us? Still no definition for "PV Disconnect" so pretty much where we were, arguing over what is the PV disconnect. Continue the fun.

Thanks. Still digesting, but what is POCC?

 

[electrofelon]

Thanks. Still digesting, but what is POCC?

Oh, got it.

 

[jaggedben]

1. Do we all agree or not that 690.13 is a DC disconnect?

In 2014 yes. In 2017 no. A giant step backwards, in my opinion. I don't think I'd fully absorbed it until just now when I got out the two books and laid them side by side.

 

[Carultch]

Thanks. Still digesting, but what is POCC?

Point of common coupling. The point where ownership by the utility meets ownership by the customer.

Examples could be the secondary terminals of a transformer, or the pole which hosts a utility-owned primary meter. It could be an underground handhole, where customer wiring is spliced to utility wiring.

In some cases it could be identical to the point of interconnection, where PV-specific equipment meets other electrical equipment, but this doesn't have to be the case.

 

[electrofelon]

Ok that all clears it up a bit. Its good to know its not just me. New rule: One English major and one philosophy major with specialty in critical thinking on each code making panel

So in practice, it seems to me that we need to know what the PV disconnect is for labeling purposes. In terms of the 690.56 requirements, would I state the location of the first DC disconnect? In my example, this would be the DC disconnect in the inverter.

 

[iwire]

Point of common coupling. The point where ownership by the utility meets ownership by the customer.

Examples could be the secondary terminals of a transformer, or the pole which hosts a utility-owned primary meter. It could be an underground handhole, where customer wiring is spliced to utility wiring.

In some cases it could be identical to the point of interconnection, where PV-specific equipment meets other electrical equipment, but this doesn't have to be the case.

Why not just call it the service point?

From article 100.

Service Point. The point of connection between the facilities
of the serving utility and the premises wiring.

 

[electrofelon]

Why not just call it the service point?

From article 100.

Duh, we are talking article 690/705 here. It has to be as confusing and convoluted as possible.

 

[iwire]

Duh, we are talking article 690/705 here. It has to be as confusing and convoluted as possible.

:lol:




Ok as long as there is a logical reason.

 

[jaggedben]

AFAIK 'point of common connection' isn't an NEC term. It's not a term that people I work with normally use either. To me it could mean the same as 'point of interconnection' which may or may not be the same as the service point or the location where the inverter connection is made, depending on who you're talking to.

Some utilities may have defined the term more explicitly, so it may be regional.

 

[pv_n00b]

Thanks. Still digesting, but what is POCC?

Point of Common Connection or Coupling, another term for the point where the PV system connects to the utility system but more commonly used in large PV systems that sell to the utility and do not feed a local load in parallel with the utility. I just like using POCC as shorthand for the PV-Utility connection. You will see it used a lot in some groups, in working with UL and various code making groups I see it pretty often. Less so elsewhere.

 

[Carultch]

Point of Common Connection or Coupling, another term for the point where the PV system connects to the utility system but more commonly used in large PV systems that sell to the utility and do not feed a local load in parallel with the utility. I just like using POCC as shorthand for the PV-Utility connection.

What if the PV first connects to on-site building loads, which then connect to the utility?

Somewhere there's gotta be a definition of the difference between POI, POCC, and Service Point.

 

[SolarPro]

What if the PV first connects to on-site building loads, which then connect to the utility?

Somewhere there's gotta be a definition of the difference between POI, POCC, and Service Point.

Agreed. It's just not in the NEC.

705.12 refers simply to the "point of connection." But the NEC does not provide a formal definition for this term. 690 refers to the "point of interconnection," but again does not provide a definition.

Article 692, Fuel Cells contains this definition:

Point of Common Coupling. The point at which the power production and distribution network and the customer interface occurs in an interactive system. Typically, this is the load side of the power network meter.

In many cases, the POCC is distinct from the "service point." In some cases, both terms could apply.

Just to muddy the water, I've talked to smart people who field a lot of PV systems and intentionally avoid the term "POCC" because utility contracts often use this to mean the "service point," which again may or may not be the point of (inter)connection for the interactive system.