Very technical question regarding the use of an AC disconnect in a PV system

[Jonathan Bruce]

I have a system we installed which, to the best of my knowledge, is fully code-compliant. The inspector in this case seems to be misled on a number of things, some of which he has dropped during our discussion. The problem at hand is as follows:

The PV modules are each individually connected to a microinverter, and the microinverters are each connected in parallel. We have <16 amps of current in each string of microinverters (2 strings total), and each string is connected via #10AWG THHN to a 20A breaker in a load-center. Power is then fed out of the load-center into a 60A non-fusible 2-pole NEMA-3R AC Siemens Disconnect, and from there go into a 40A breaker in the MSP.

The inspector is quoting (2017) NEC 690.13(f)2 in stating that I cannot use a disconnect which is marked "line" and "load", since they are not suitable for backfeed or reverse current. However, as far as I have been able to find, all UL-listed AC disconnects are marked "line" and "load". None of my suppliers have any such disconnect in their systems. Furthermore, and more importantly, I maintain that having an AC disconnect for this purpose NOT marked "line" and "load" is inherently very dangerous; any technician coming to service the system in the future will not have the source of power clearly marked, and could be led to believe that when the disconnect is turned off, that there is no longer power being supplied or could be led to believe that power is coming from the solar side, which it cannot as rapid shut-down functionality is built into the microinverters (as is required).

For breakers, this code reference makes sense as they are electronic in nature rather than purely mechanical; however, for a mechanical AC disconnect it seems very unreasonable to state that they are not suitable for "reverse" current, since with AC the current flows both ways, 60 times per second, and there are no diodes or sensors which could be in any way damaged by a current from the "wrong" side.

I would appreciate any information or references which could help to clarify this. It's been an ongoing problem/discussion for months.

 

[steve66]

I would note f(1) which calls for a "externally operable general use switch or circuit breaker, or other approved means".

If the inspector isn't willing to approve an Air Conditioner disconnect (which I assume is what you mean by an "AC disconnect"), I'd say he is well within his right.

 

[wwhitney]

So what purpose does the "60A non-fusible 2-pole NEMA-3R AC Siemens Disconnect" serve that the "40A breaker in the MSP" doesn't? If the "40A breaker in the MSP" satisfies the requirements of 690.13, does 690.13(F) apply to the additional disconnect?

Cheers, Wayne

 

[GoldDigger]

The big reason for marking a mechanical AC disconnect for Line and Load is to have the smallest number of surfaces (including fuse holders if present) inside the disconnect enclosure still be live when the disconnect is open.
Where that is a governing concern, a Solar PV disconnect will never have voltage present on the Load side of the disconnect when open because of anti-islanding. So backwards installation in terms of power flow is not a real concern.

 

[Jonathan Bruce]

I would note f(1) which calls for a "externally operable general use switch or circuit breaker, or other approved means".

If the inspector isn't willing to approve an Air Conditioner disconnect (which I assume is what you mean by an "AC disconnect"), I'd say he is well within his right.

The AC disconnect is an alternating current disconnect, as opposed to a DC disconnect.

So what purpose does the "60A non-fusible 2-pole NEMA-3R AC Siemens Disconnect" serve that the "40A breaker in the MSP" doesn't? If the "40A breaker in the MSP" satisfies the requirements of 690.13, does 690.13(F) apply to the additional disconnect?

Cheers, Wayne

The breaker in the MSP is inside the house, and a externally operated disconnect is required to be within sight of the meter, and generally inspectors prefer it to be right beside the meter so that it is easily accessible by firemen during the case of a fire. So we have this disconnect outside, by the meter. As to whether13(f) applies if the breakers satisfies the requirements, that's a good question. I'll bring that up in my next interaction.

The big reason for marking a mechanical AC disconnect for Line and Load is to have the smallest number of surfaces (including fuse holders if present) inside the disconnect enclosure still be live when the disconnect is open.
Where that is a governing concern, a Solar PV disconnect will never have voltage present on the Load side of the disconnect when open because of anti-islanding. So backwards installation in terms of power flow is not a real concern.

I've tried telling the inspector about the anti-islanding of the micro-inverters. He appears to think it is irrelevant.

 

[GoldDigger]

The AC disconnect is an alternating current disconnect, as opposed to a DC disconnect.


The breaker in the MSP is inside the house, and a externally operated disconnect is required to be within sight of the meter, and generally inspectors prefer it to be right beside the meter so that it is easily accessible by firemen during the case of a fire. So we have this disconnect outside, by the meter. As to whether13(f) applies if the breakers satisfies the requirements, that's a good question. I'll bring that up in my next interaction.


I've tried telling the inspector about the anti-islanding of the micro-inverters. He appears to think it is irrelevant.

He appears to be incompetent. (and, for the Perry Mason fans out there, immaterial?)

 

[wwhitney]

The breaker in the MSP is inside the house, and a externally operated disconnect is required to be within sight of the meter

Where is that requirement in the NEC? It's not in 690.13(A), which covers the location of the PV System Disconnecting Means. So the phrase "externally operable" in 690.13(F) is referring to how you operate the disconnect, not its location.

Then if the outdoor disconnect is a POCO requirement, and not an NEC requirement, that is further support for the argument that it is not subject to 690.13, with the breaker in the MSP serving as the NEC 690.13 disconnect.

Cheers, Wayne

 

[Jonathan Bruce]

Where is that requirement in the NEC? It's not in 690.13(A), which covers the location of the PV System Disconnecting Means. So the phrase "externally operable" in 690.13(F) is referring to how you operate the disconnect, not its location.

Then if the outdoor disconnect is a POCO requirement, and not an NEC requirement, that is further support for the argument that it is not subject to 690.13, with the breaker in the MSP serving as the NEC 690.13 disconnect.

Cheers, Wayne

690.12(C) states that the disconnecting means (rapid shutdown requirement) must be outside the building for one- and two-family dwellings. I'm not seeing the part that says within sight of the meter; perhaps that's a local requirement and I'm getting mixed up on that.

 

[steve66]

The AC disconnect is an alternating current disconnect, as opposed to a DC disconnect.

It wasn't 100% clear to me if you meant Alternating Current, or Air Conditioning.

From the context of your message, I thought you were using an Air Conditioning Disconnect, which is sometimes referred to as a pullout. I could see the inspector flagging that - it would be a really cheap way to go.

So the only issue is the line and load markings on the disconnect? That's only not allowed for backfeed or reverse current, which you aren't doing, assuming you have the panels connected to the "line" side.

 

[wwhitney]

690.12(C) states that the disconnecting means (rapid shutdown requirement) must be outside the building for one- and two-family dwellings.

Ah, yes, the 690.12(C) RSD initiation device. But that doesn't have to be the same as the PV disconnecting means.

If your AC disconnect is a "Readily accessible switch that plainly indicates whether it is in the “off” or “on” position" then it qualifies under 690.12(C)(3) as your RSD initiation device without being your PV disconnecting means. And then your MSP 40A breaker would be your PV disconnecting means.

Which means that the outdoor AC disconnect is not subject to 690.13, and the MSP 40A breaker is not subject to 690.12(C).

Cheers, Wayne

 

[Jonathan Bruce]

It wasn't 100% clear to me if you meant Alternating Current, or Air Conditioning.

From the context of your message, I thought you were using an Air Conditioning Disconnect, which is sometimes referred to as a pullout. I could see the inspector flagging that - it would be a really cheap way to go.

So the only issue is the line and load markings on the disconnect? That's only not allowed for backfeed or reverse current, which you aren't doing, assuming you have the panels connected to the "line" side.

I understand the confusion. I'll be more clear next time.
We generally have the panels connected to the "line" side, though some inspectors have required us to switch it around (uncommon but it happens).

Ah, yes, the 690.12(C) RSD initiation device. But that doesn't have to be the same as the PV disconnecting means.

If your AC disconnect is a "Readily accessible switch that plainly indicates whether it is in the “off” or “on” position" then it qualifies under 690.12(C)(3) as your RSD initiation device without being your PV disconnecting means. And then your MSP 40A breaker would be your PV disconnecting means.

Which means that the outdoor AC disconnect is not subject to 690.13, and the MSP 40A breaker is not subject to 690.12(C).

Cheers, Wayne

You and Steve are making good points. Thanks so much for your help. I'll compile everything and bring it to the inspector and let you all know what happens.

 

[wwhitney]

We generally have the panels connected to the "line" side, though some inspectors have required us to switch it around (uncommon but it happens).

"Panels" is ambiguous in this context. The "line" side should be the side that is energized (by the grid) when the disconnect is open.

Cheers, Wayne

 

[synchro]

FYI, the 2020 NEC has changed this line/load requirement on a disconnect to an informational note that is limited to just circuit breakers:

690.13(E) Type of Disconnect
...
"Informational Note: Circuit breakers marked “line” and “load” may not be suitable for backfeed or reverse current."

 

[mtnelect]

Does your installation look something like this ?

 

[Fred B]

This concern over both/either line/load sides could potentially be energized regardless of switch positions is the rationale for proper marking that indicates this issue, like signage at bottom of picture. Also a requirement in 690.13(B). If line/load marked switches were NOT allowed this requirement would not be in place.

 

[Jonathan Bruce]

"Panels" is ambiguous in this context. The "line" side should be the side that is energized (by the grid) when the disconnect is open.

Cheers, Wayne

That's true. Panels should be been "PV Modules".
As to the connectivity, given that the electricity only ever flows from the PV array to the grid, most inspectors require the PV array to be connected to the "line" side of the disconnect. It is safer to do the opposite, but more code compliant their way. In the end, you do whatever the inspector insists.

FYI, the 2020 NEC has changed this line/load requirement on a disconnect to an informational note that is limited to just circuit breakers:

690.13(E) Type of Disconnect
...
"Informational Note: Circuit breakers marked “line” and “load” may not be suitable for backfeed or reverse current."

Yeah, I'm looking forward to the adoption of the 2022. There's a significant increase in PV clarification since 2017.

Does your installation look something like this ?

Somewhat, yes. In general the 1-line does.

This concern over both/either line/load sides could potentially be energized regardless of switch positions is the rationale for proper marking that indicates this issue, like signage at bottom of picture. Also a requirement in 690.13(B). If line/load marked switches were NOT allowed this requirement would not be in place.

View attachment 2560892

You make a great point. The signage is only specified because line/load marked disconnects are suitable for use. I'll bring that up if last night's email doesn't pan out.

 

[jaggedben]

I never noticed before what a horrible mistake the CMP made with that section. (690.13 F 2). That was only there for one code cycle.