600Vdc PV Disconnect

[wwhitney]

How is it not? If the disconnect were on the other side of the inverter, it is a PV system disconnect, not a DC PV system disconnect. It has to be on the DC side of the inverter to be a DC PV system disconnect, so it is before the inverter.

Not every PV system uses inverters. Given the requirements for a PV system disconnect as listed in 690.13, a DC PV system disconnect only exists in PV installations with DC loads and no inverters, as jaggedben commented. That's why in the list in the definition of PV DC Source Circuit, the item "DC PV system disconnect" comes after "electronic power converters," it is to cover the case there are no electronic power converters at all.

The DC disconnect in a system with an inverter doesn't obviate 690.12 by avoiding the existence of controlled conductors; it may satisfy 690.12 by being the rapid shutdown initiation device for the controlled conductors on the grid side of the DC disconnect.

Cheers, Wayne

 

[solarken]

I see it slightly differently...

RSD requirements only apply to conductors installed on or in buildings. That's in the first sentence of 690.12. From there, controlled conductors are subdivided into two categories: within and without the array boundary. For a groundmount, you have no conductors that are both within the array boundary and on or in a buidling, so we can dispense with worrying about those requirements. However, you've described bringing a PV DC circuit on or in a building to an inverter. So now that portion of the circuit that is on or in the building is controlled. But in my opinion, that only applies to that portion that is on or in the building. By putting a DC disconnect at the point where they come onto the building, or at a readily accessible point before that, you provide an initiation device that allows the contrlled conductors on/in the building to meet the requirements when the disconnect is opened.

One loophole that I don't think was intended is that they don't specify how far away from the building your rapid shutdown switch can be. If it's 1000ft away I think that violates the intent of the requirement, although not the letter. They should have required the initiation device to be at a "readily accessible location outside *and within sight of* the building". i.e. no more than 50ft away. If it were me, I wouldn't push your interpretation too hard with an AHJ if the groundmount were farther away than that.

But a PV dc circuit brought to the external wall of a building and terminating on a DC disconnect is covered by the Exception in 690.12(A), which specifies they are not controlled conductors, it does not say that having the disconnect there serves to rapidly shut down the conductors. I think there is a lot of improvement that can be made to the wording in 690.12. It should be clear that denergizing conductors using a DC disconnect means those conductors either don't need to be controlled, or that the DC disconnect serves as that control, to eliminate it from needing other rapid shutdown equipment. The bottom line is we should not have to incur the expense and trouble of adding rapid shutdown equipment when there is no danger to emergency personnel (by energized conductors) climbing on a roof or entering a building.

 

[wwhitney]

But a PV dc circuit brought to the external wall of a building and terminating on a DC disconnect is covered by the Exception in 690.12(A)

No, you'd have to have the inverter on the exterior wall of the building to use 690.12(A) Exception, as the conductors between the DC disconnect and the inverter are still controlled conductors.

Cheers, Wayne

 

[jaggedben]

The diagrams in figure 690.1(b) show examples of what is considered the PV System Disconnect in different configurations, including the somple interactive system where the PV System Disconnect is on the AC side of the inverter.

 

[jaggedben]

The diagrams in figure 690.1(b) show examples of what is considered the PV System Disconnect in different configurations, including the somple interactive system where the PV System Disconnect is on the AC side of the inverter.

Crap, nevermind, they got rid of those in 2023, too. They really fumbled all this. There's no consistency in terminology anymore.

 

[jaggedben]

But a PV dc circuit brought to the external wall of a building and terminating on a DC disconnect is covered by the Exception in 690.12(A), which specifies they are not controlled conductors, it does not say that having the disconnect there serves to rapidly shut down the conductors. I think there is a lot of improvement that can be made to the wording in 690.12. It should be clear that denergizing conductors using a DC disconnect means those conductors either don't need to be controlled, or that the DC disconnect serves as that control, to eliminate it from needing other rapid shutdown equipment. The bottom line is we should not have to incur the expense and trouble of adding rapid shutdown equipment when there is no danger to emergency personnel (by energized conductors) climbing on a roof or entering a building.

We agree that the conductors from a ground mount that terminate on an external disconnect aren't controlled conductors. What we apparently don't agree on is whether conductors on the inverter side of the disconnect are controlled conductors. But I say they clearly are, because they are PV System DC circuits in or on the building.

 

[solarken]

We agree that the conductors from a ground mount that terminate on an external disconnect aren't controlled conductors. What we apparently don't agree on is whether conductors on the inverter side of the disconnect are controlled conductors. But I say they clearly are, because they are PV System DC circuits in or on the building.

Not every PV system uses inverters. Given the requirements for a PV system disconnect as listed in 690.13, a DC PV system disconnect only exists in PV installations with DC loads and no inverters, as jaggedben commented. That's why in the list in the definition of PV DC Source Circuit, the item "DC PV system disconnect" comes after "electronic power converters," it is to cover the case there are no electronic power converters at all.

The DC disconnect in a system with an inverter doesn't obviate 690.12 by avoiding the existence of controlled conductors; it may satisfy 690.12 by being the rapid shutdown initiation device for the controlled conductors on the grid side of the DC disconnect.

Cheers, Wayne

But why would a PV system with no inverter be considered to have DC conductors after a DC disconnect be safe for emergency personnel, but not if those same conductors were to land on an inverter? The DC disconnect terminates the conductor in either case. You turn off the disconnect, and the conductors are dead. Suppose I had a 600V heater element in the home, with conductors running from the heater out thru the wall of the home into conduit under ground, coming up at the ground mounted array, and into a DC disconnect, before connecting to the PV strings. Are you saying the conductors between the DC disconnect and the heater element are not controlled conductors, but if instead there were an inverter connected instead of a heater element, that they would be controlled conductors?

I view the DC disconnect as terminating the DC PV source conductors for the purpose of 690.12 rapid shutdown in either case.

I think the NEC needs a revision to include an exception from 690.12 for conductors downstream of a DC disconnect. it would eliminate the confusion and conflicting interpretation.

 

[jaggedben]

But why would a PV system with no inverter be considered to have DC conductors after a DC disconnect be safe for emergency personnel, but not if those same conductors were to land on an inverter?

No one ever said this. The distinction just came up because you pointed to the definition of PV System Conductors and its reference to a DC PV System Disconnecting Means, and your wanting to ignore the word 'system' and any meaning that word might have. Safety wise, if the DC disconnect can be considered a PV System Disconnect because everything after it is distribution feeder(s) or branch circuits, then other sections of the code cover those requirements. For example if your groundmount were for a stand-alone system powering an off-grid cabin, then your DC disconnect would just be the feeder disconnect required in Article 225.

I suppose in the bigger picture it's somewhat inconsequential, since Article 225 already requires a disconnect at the building, and Articles 705 and 710 and 225.37 already require signage for all power sources at a building. So regardless, you are going to be putting a DC disconnect on the house (not at the groundmount, or at any rate that one doesn't count.) And you'll be placarding and mapping your DC disconnect for emergency responders if there's also a utility service on the house. However the devil is in the details, with things like whether the switch has to be outside to meet 690.12 and which label needs to be applied.

Suppose I had a 600V heater element in the home, with conductors running from the heater out thru the wall of the home into conduit under ground, coming up at the ground mounted array, and into a DC disconnect, before connecting to the PV strings. Are you saying the conductors between the DC disconnect and the heater element are not controlled conductors, but if instead there were an inverter connected instead of a heater element, that they would be controlled conductors?

Yes. Because of the definition of PV System Conductors you pointed out. But note that your DC disconnect for the heater circuit on the building is just the feeder disconnect which is required to be installed and called out in a directory by article 225.

Actually there is another reason, which should potentially concern you. Some inverters continue to the energize DC conductors when disconnected from the arrays because of capacitors in the inverter. So this potentially makes conductors going to inverters actually more dangerous, which is an argument for applying rapid shutdown to those conductors. Depends on the inverter. I don't believe this is an issue with SMA but it was with SolarEdge.

I think the NEC needs a revision to include an exception from 690.12 for conductors downstream of a DC disconnect. it would eliminate the confusion and conflicting interpretation.

I would submit a comment against such a revision. Such a DC disconnect might be inside or not readily accessible and then the intent of rapid shutdown might not be met. The confusion created by the revisions to the PV DC circuit definitions was clearly not intended to create such a distinction.

 

[ggunn]

How does it not do that in this case? Also 690.12 does not require that the RSD switch be grouped with the service disconnect.

Please do not make up code rules based merely on your usual way of doing things.

Arrrrgh! Ya got me, pardner. You'd think that by now I would have learned not to try to apply common sense to the NEC. I would hope that there would at least be a placard at the MSD to indicate to first responders that there are DC conductors going into the building at another point that would still be energized when the power is shut off, and where the DC disco is.

 

[solarken]

What about just manual switches at the array like IMO S132-PEL64R-4. Its good for 32 amps and 2 strings.

I have been looking over the IMO Solar products catalog, and if I am not missing something, those SIxx-PEL isolators do not have contacts rated for the current that appears in their model number. For example, the SI32-PEL64R-4 you reference is rated for 32A at 600V only with two poles in series, and it's rating for only 1-pole is 6A at 600V. So a 4-pole isolator like that could only break 1 string (pos and neg) and would have to be wired for two poles in series per leg. Not saying they are bad devices, but their catalog is misleading as it shows solar wiring examples that appear to use single pole breaks but that do not match the tables with the UL specs, or even the table with the IEC specs.

 

[scrubbin]

I contacted the manufacturer and this is was their reply:

 

[jaggedben]

Note that if you take a 2-pole and run positive through one pole and negative through the other pole that's still 2 poles in series.

 

[solarken]

I contacted the manufacturer and this is was their reply:
View attachment 2572959

Doh! It is clear now, not sure why my brain had a tough time looking it like that.

 

[Jraef]

The Siemens HNF361 is only rated for 250vdc.

Siemens has a version of their disconnects specifically for solar PV systems, it’s rated for 600VDC. I don’t remember the number suffix they put on the end any longer, but it’s available. When I worked there (over 15 years ago), I was on the development team for it. They use two poles in series to increase the voltage rating, but also put in a set of permanent magnet arc blow-outs. That makes it more expensive than the non-solar version of course, but it gets you there.

Edit: to any HD disconnect part number, up to 200A, you add “RPV” to the end for the solar PV rated version. So it would be an HNF361RPV for the version rated for 600VDC.