Do you need a disconnect at a ground-mounted array?

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tortuga

Code Historian
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Oregon
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Electrical Design
No, it's not unless an isolation transformer is between it and the service.
Are we talking about an inverter on the pole in question then AC feeder?

I am was picturing :
pole mounted array Photovoltaic Source Circuit ---> combiner box ---> Photovoltaic Output Circuit ---> going underground leaving the structure ---> to an inverter mounted on another pole or structure.
 

jaggedben

Senior Member
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Solar and Energy Storage Installer
I just had to revisit this question for I project I am working on and I'll add to this.
I still think article 225 applies but since the feeder is 'leaving' the pole I no longer think 225.31 applies :) in this case.

A pole mount PV array is a Separately Derived System that supplies a feeder to another structure 690 does not modify that.
Explanation:
Per 90.3 article 690 can subtract a specific requirement of article 225 but it must do so explicitly, which it does not do.
For example recently the 2017 NEC deleted the redundant 690.3 requirement based on "proper use of code structure per 90.3".

Code:
2014 NEC 690.3 Other Articles
Wherever the requirements of other articles of this Code and
Article 690 differ, the requirements of Article 690 shall apply
and, if the system is operated in parallel with a primary source(s)
of electricity, the requirements in 705.14, 705.16, 705.32, and
705.143 shall apply.

Article 225.1 Scope states
Code:
This article covers requirements for outside branch circuits and feeders run on or between buildings, structures, or poles on the premises.."
Table 225.3 goes on to mention article 690.

690 does define the Photovoltaic Output Circuit:
Code:
Circuit conductors between the PV source circuit(s) and the inverter or dc utilization equipment.
We have a pole mounted array and we need to run a Photovoltaic Output Circuit from the pole(s) to the inverter or dc utilization equipment.
Per the definition that is both a feeder and a 'Photovoltaic Output Circuit'.

For example there are other cases where something can meet more than one code definition a common recessed can light meets the definition of luminaire and that of an outlet.


sketchy: can you find out from the AHJ what specific code section they are talking about? I am curious if it really is a local code or an interpretation of 225.31.

I don't agree with any of your points.

A PV Array is usually not a separately derived system these days, but even if it were, that would not make a DC PV Output Circuit into a Feeder. Neither PV source circuits nor inverters resemble any of the branch circuit definitions, nor are they required in all cases to have overcurrent devices on the DC side. Therefore the definition of a feeder simply does not apply since the presence of branch circuit overcurrent devices at one end is essential to that definition.

Again, if you are supplying AC to the structure, then the normal feeder and branch circuit definitions reasonably apply. But for DC, not so much.
 

romex jockey

Senior Member
Location
Vermont
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electrician
If AC were run out to the ground mount, I would say per 225 we might need a disconnect. I say might because of the revised definition of "structure" and "equipment" is now not a structure. It's a bit gray to me. Its really just academic tho as most inverters have AC disconnects, and a combiner panel will usually have less than 6 throws if MLO.

Just for completeness, one thing I have done is use 230.40 exception 3 to serve a ground mount. In that case of course there needs to be service disconnect.


so is a PV pedestal considered a feeder, an SDS, or service entrance?
:unsure:
~RJ~
 

jaggedben

Senior Member
Location
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Solar and Energy Storage Installer
so is a PV pedestal considered a feeder, an SDS, or service entrance?
:unsure:
~RJ~

If it's an AC side circuit, it's the same thing as it would be if PV weren't connected. So apply the relevant rules of 225, 230 etc. It is also an inverter output circuit. So you also apply the rules of 705 to that circuit. So far as I've noticed this doesn't create conflicts.

If it's a DC PV circuit (including 'DC-to-DC Converter' circuits, i.e. optimizer output circuits) then I don't believe any of the article 100 definitions strictly apply. The definitions and rules in 690 are all that strictly apply.

Arguably many of the requirements of 225 or 230 ought to apply for safety reasons, but I don't believe there's a strictly logical argument for that or a way to figure it out. You just sort of have to apply a common sense test and be reasonable. For example in this thread people are arguing for applying 225.31 to PV circuits. Okay then, what about 225.39, which establishes minimum disconnect ratings such as 100A for a single-family dwelling? It makes absolutely no sense to apply that to PV circuits. Or to give another example, say someone wanted to install a PV output circuit between buildings overhead on a messenger, which is not prohibited as far as I know. Which clearance rules should apply? 225 or 230? None? Since there are no call-outs in 690, you're really just making your best guess.

Finally, I should add that I think it would often be a good idea to install a disconnect for the DC output at a ground mount, and in some cases a particular design would end up requiring it. For example if you have a fused PV DC combiner there, the requirements for being able to isolate it would kick in. If you just have a couple strings paralled in a j-box, I'd argue for letting that pass.
 

wwhitney

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If it's a DC PV circuit (including 'DC-to-DC Converter' circuits, i.e. optimizer output circuits) then I don't believe any of the article 100 definitions strictly apply. The definitions and rules in 690 are all that strictly apply.
I would have to disagree. If you had a service with PV interconnected and absolutely no utilization equipment (is that even possible?) then perhaps.

Otherwise, as soon as you have utilization equipment, you have a branch circuit and branch circuit OCPD. Then "all circuit conductors between the . . . power supply source and the final branch-circuit overcurrent device" are feeders. It doesn't matter whether those conductors are carrying AC or DC.

Cheers, Wayne
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Are we talking about an inverter on the pole in question then AC feeder?

I am was picturing :
pole mounted array Photovoltaic Source Circuit ---> combiner box ---> Photovoltaic Output Circuit ---> going underground leaving the structure ---> to an inverter mounted on another pole or structure.
I got that; it's not separately derived. Look up the definition of an SDS; it should be clear.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
How is a PV system not an electrical source?
Code:
Separately Derived System. An electrical source, other than
a service, having no direct connection(s) to circuit conductors
of any other electrical source other than those established by
grounding and bonding connections. (CMP-5)
And in my 2017 Handbook the commentary:
Examples of separately derived systems include ... solar photovoltaic systems.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Since were talking about a DC Photovoltaic Output Circuit (Feeder):
...
If it's a DC PV circuit (including 'DC-to-DC Converter' circuits, i.e. optimizer output circuits) then I don't believe any of the article 100 definitions strictly apply. The definitions and rules in 690 are all that strictly apply...
That statement is contrary to 90.3 code structure. Chapters 1-4 apply generally.
The definitions in 100 apply to 690 and remain in effect in 690.

...Arguably many of the requirements of 225 or 230 ought to apply for safety reasons, but I don't believe there's a strictly logical ..
Ben Nothing in 230 would apply to a PV system since a PV system is not a service.
225 applies to the DC Photovoltaic Output Circuit the OP was talking about as it also meets the definition.
 
Ben Nothing in 230 would apply to a PV system since a PV system is not a service.
225 applies to the DC Photovoltaic Output Circuit the OP was talking about as it also meets the definition.

We are getting dangerously close to the dreaded "is a supply side pv connection disconnect a service disconnect" discussion. But just as a response to your specific claim, see 230.40 exception #5 which mentions 230.82(6) which reads, "solar photovoltaic systems."
 
How is a PV system not an electrical source?
Code:
Separately Derived System. An electrical source, other than
a service, having no direct connection(s) to circuit conductors
of any other electrical source other than those established by
grounding and bonding connections. (CMP-5)
And in my 2017 Handbook the commentary:
Examples of separately derived systems include ... solar photovoltaic systems.

It is not whether something is a "source" that makes it an SDS or not. The key part is the "having no direct electrical connection...." part. A transformer based inverter could provide isolation between the DC conductors and the AC conductors making it technically an SDS. Most modern inverters do not have a transformer so there is direct electrical connection between the AC and DC sides, granted through a bunch of electronics doing lots of rapid switching and holding energy in inductors and capacitors, but there is not isolotion.

In post 19 I stated, " The concept of an SDS never really was applied to PV systems." What I meant was although the definition could technically apply in some situations, the system grounding of PV systems was treated separately (and a horrible mess for many code cycles) in article 690 and was based on "ungrounded" vs "grounded" instead of isolated vs unisolated.
 

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Ahh yes 230.82 good point on that.

If there was any direct electrical connection between the AC side and DC side of a UL 1741 grid interactive inverter it would fail the UL 1741 47.3 Short-circuit test.
There is no direct electrical connection between the DC and AC side.
If a bolted DC fault happens no AC can flow on the DC side of the inverter etc.
 
If there was any direct electrical connection between the AC side and DC side of a UL 1741 grid interactive inverter it would fail the UL 1741 47.3 Short-circuit test.
There is no direct electrical connection between the DC and AC side.
If a bolted DC fault happens no AC can flow on the DC side of the inverter etc.


I Admit I do not know the specifics of that test or the electronics inside the inverter. Perhaps the electronics inside break the AC/DC connection upon sensing a fault. These things can sense a fault and open very very quickly. I dont believe there is any way to achieve isolation without a transformer. I suppose one could store energy in capacitors and inductors, break the circuit, and then release it, repeat, but I do not think the AC and DC side are never connected like that.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I would have to disagree. If you had a service with PV interconnected and absolutely no utilization equipment (is that even possible?) then perhaps.

Otherwise, as soon as you have utilization equipment, you have a branch circuit and branch circuit OCPD. Then "all circuit conductors between the . . . power supply source and the final branch-circuit overcurrent device" are feeders. It doesn't matter whether those conductors are carrying AC or DC.

Cheers, Wayne

Since were talking about a DC Photovoltaic Output Circuit (Feeder):

That statement is contrary to 90.3 code structure. Chapters 1-4 apply generally.
The definitions in 100 apply to 690 and remain in effect in 690.

Ben Nothing in 230 would apply to a PV system since a PV system is not a service.
225 applies to the DC Photovoltaic Output Circuit the OP was talking about as it also meets the definition.

Guys, stop and look at what you're doing. It seems to me you're engaging in a kind of ultra-legalistic, Rube Golberg contraption way of getting to the conclusion you want to get to. (Well, maybe Wayne is just being argumentative in hope of a lively discussion, but my following points still stand... ;) ). Stop pretending that the code clearly states something that it does not clearly state. These are your interpretations, and they are pretty down-the-rabbit-hole interpretations in my opinion. When I said 'strictly', twice, in post #25, that was pointed. It is clear that 225 applies to AC circuits connecting a PV system, and it is clear that 690 applies to the DC circuits in a PV system. But whether 225 applies to DC circuits involves a lot of parsing the meaning of particular words, and is not going to be settled by a forum thread. Your AHJ is not going to be up to speed on this whole conversation.

Wayne, as you yourself seem to acknowledge, there might be some PV systems where the particular arrangement of a PV circuit and other equipment on site seems to meet the definition of a feeder, and others where it does not. From a safety point of view, which is the purpose of the code, such uneven enforcement based on philosophical parsing would not be responsible.

Tortuga, I'm not going to be convinced that the definition of a feeder strictly applies to PV source or output circuits based on what the code says. 225 no more strictly applies than 230, that was the point about 230. I'm much more easily convinced that at least some of the rules in 225 ought to apply, even if the code doesn't clearly say so. Because without applying some rules or other to certain aspects (e.g. clearances), some PV systems could be unsafe, and that is what goes against why we're all here. And because 225 is the most sensible article to apply, although not in its entirety (see above).

But in order to apply that reasoning to requiring a DC disconnect at a ground mount array per 225.31, you'd have to explain to me why not having the disconnect would make the installation unsafe. When we instead get into these word-parsing interpretation battles, we end up with AHJs placing undue burdens on installers when there's really no safety issue, such as in the case of this poor guy.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Ahh yes 230.82 good point on that.

If there was any direct electrical connection between the AC side and DC side of a UL 1741 grid interactive inverter it would fail the UL 1741 47.3 Short-circuit test.
There is no direct electrical connection between the DC and AC side.
If a bolted DC fault happens no AC can flow on the DC side of the inverter etc.

I think you are not fully informed here. I don't know the text of the 47.3 test either, but I know for sure that the transistors in non-isolated inverters directly connect DC to AC. That is, power flows entirely via electrons on conductors, and not via magnetic flux like in a transformer. Since PV panels are a semi-conductor, this does not result in a short circuit unless the inverter's transistors make the connections in the wrong direction (i.e. not synced correctly with the AC waveform), which would be precisely what they wouldn't do in order to pass the UL test.

Finally, I've seen cases in non-isolated inverters where I'm pretty sure that AC current has flown through the DC wiring in a fault, and tripped a fuse. And those were UL listed inverters.
 

wwhitney

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Location
Berkeley, CA
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Retired
If we are talking DC, I think it's doubtful we have any 'feeders'. 690 defines DC circuits in ways that exclude all parts of other circuits that are definitely feeders, and Chapter 6 takes precedence over Chapter 2.
Sorry, I missed this the first time through, this is my point of disagreement:

(2014) 90.3 says in part "Chapters 1, 2, 3, and 4 apply generally; Chapters 5, 6, and 7 apply to special occupancies, special equipment, or other
special conditions. These latter chapters supplement or modify the general rules. Chapters 1 through 4 apply except as amended by Chapters 5, 6, and 7 for the particular conditions."

So unless Article 690 is amending the definition of feeder, the Chapter 1 feeder definition applies, and Article 225 applies to anything meeting that definition. Just because 690 defines some conductors as, say, PV output conductors doesn't mean that those conductors can't also be feeders.
And the DC conductors will almost always meet the definition of feeder. [Edit: the alternative is that the DC conductors are branch circuit conductors, in which Article 225 still applies.]

Cheers, Wayne
 
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jaggedben

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It's not a chapters 1-4 vs 5-7 issue. That's a red herring in the discussion. That only comes into play if you accept the premise that any of the Article 100 definitions, in the plain English language meanings of the words and in the context of each other, clearly apply to PV source and output circuits. I maintain that PV source and output circuits do not clearly fall into the English language meanings of the Article 100 definitions, and therefore it is impossible to know, at least on a strict letter-of-the-code basis, how to apply articles in Chapter 2.

Edit: once again you acknowledge that there are weaknesses with insisting there can be a strict interpretation, when you say well maybe they're feeders and maybe they're branch circuits. There is nowhere in the code where it states that every circuit must be a service, feeder, or branch circuit.
 
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wwhitney

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when you say well maybe they're feeders and maybe they're branch circuits.
Yeah, that's not what I said exactly. They are basically always feeders. The one case I can think of where they are branch circuits would be a standalone PV system connected directly to a piece of utilization equipment without any OCPD.

There is nowhere in the code where it states that every circuit must be a service, feeder, or branch circuit.
No, but as soon as there is a piece of utilization equipment connected, that is the logical corollary of the definitions. (One circuit being both a branch circuit and a feeder is also a possibility.) Can you provide a counterexample?

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
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Solar and Energy Storage Installer
Yeah, that's not what I said exactly. They are basically always feeders. The one case I can think of where they are branch circuits would be a standalone PV system connected directly to a piece of utilization equipment without any OCPD.

No, but as soon as there is a piece of utilization equipment connected, that is the logical corollary of the definitions. (One circuit being both a branch circuit and a feeder is also a possibility.) Can you provide a counterexample?

My position is simply that the language is too ambiguous with respect to PV systems. In any system with an inverter you would need to characterize the inverter as something that appears in the definitions of branch circuits and feeders, and it is not clear how to do so. Your line of thought would be particularly problematic in the case of any isolated inverter where the DC conductors do not connect to a system with branch circuits. But I'm really not interested in that particular line of argument; it's just another example of how that type of approach to the question leads to self-involved discussions and wrong conclusions. We shouldn't be applying 225 to some PV systems and not others depending on their exact topology. And we shouldn't be applying 225.39 to any PV system circuits, just to pick the most salient example from that article.

Once again, someone please offer an argument why a ground-mounted array without a disconnect is unsafe. The code section that justifies my position is 90.1
 
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