California Rapid Shutdown Requirements

[pgrovetom]

When neither a ground mount solar string array nor the inverters are located within 50 ft of a building ( both are completely outdoors away from any building), are panel rapid shutdown devices required in California for a standard ground string array?

The solar array is mounted on a gentle hillside about 100 feet of the home on a steel frame with 18" underground conduits carrying the DC string pairs to the Inverter. The Inverter has a built in and labeled DC disconnect for those DC lines. The inverters are mounted on a pressure treated wood post structure similar to the utility post intended to provide some sun/weather protection and a place to physically mount the inverters. There are 3 Tesla Powerwall2's mounted on a concrete pad adjacent to the inverter PT posts mounting structure. The PG&E utility power arrives underground to the base of a 4x6" pole mounted 400A panel which acts as the place where the inverter/battery system meets the AC wires that go to the home via underground approximately 50+ ft conduits. There are multiple sub-panels inside the home. The AC power from the inverter/Powerwall2 battery system have 200A panels and breakers and are carried via a trough system to the top of the utility 4x6" post.

The utility comes up the 4x6" post from an underground conduit into the 400A panel. The AC for the home goes via conduits down the 400A panel on the 4x6" post and underground to the home's sub-panels. So neither the inverters nor the ground mount solar arrays DC penetrates or even gets near the home in any way. The DC does not come within 50 feet of the home. Only the AC from the utility or inverters penetrate the home via conduits as it was before the solar was installed. The NEC language suggests this situation does not require a rapid shutdown function for the solar arrays/panels.

My system was installed by Tesla and permitted and built in 2019. The reason I am asking is I'm thinking of adding an additional ground mount array and another inverter. If I do this, will it now require the array rapid shut down function given there has been 2 NEC updates since 2019 with slightly different language. The language of the NEC suggests if the DC does not penetrate the building ( i.e home), which it does not, then rapid shutdown is not required. But the language of the NEC also uses the term "building" and who knows if the posts and steel array structure qualify as a building. So I'm hoping to understand if my situation would require the rapid shutdown function should I choose to add the new array. If so, would it be retroactive and also be imposed on the existing 2019 system requiring rapid shutdown devices on every panel? Any thoughts appreciated.

 

[FilterGuy]

The way I read the code you should not need the rapid shut down.

Note that even if the call your post a structure. It is dedicated to solar and therefore has a few exceptions to the rules

 

[Brucey]

Out my way it's more a case of is it a dwelling, or an accessory structure? Far less requirements for the latter.

 

[Skypower]

Don’t give the state of confusion any ideas.

 

[Kuma]

I recommend going to the bldg dpt first. But, dont quote that code stuff to them unless youre certain it helps you. Let them decide. I live in Placer County and had several questions about installing roof top solar last year. Did a walk in at the bldg dept with a hand drawing of the roof top solar. They were very nice, helpful and even allowed some deviation from the fire dept setbacks rules.

 

[pgrovetom]

The way I read the code you should not need the rapid shut down.

Note that even if the call your post a structure. It is dedicated to solar and therefore has a few exceptions to the rules

Thanks. That's how I read it. I'm also considering helping a friend build a new system based on a ground mount similar to mine but with a Hybrid Inverter and Batteries in the garage. I also read that this situation may not need rapid shutdown. Is that true or do they allow a DC disconnect at the house entry point, either manual or automatic. It would seem that this case is like the utility power, gas etc... where the fire fighters kill a main breaker or gas valve at the home entry. Since almost all the DC string power is 24" in conduit underground and only arises to enter the home at one point, wouldn't a DC disconnect that's manual or automatic work in that case. No rooftop. I'm trying to learn most of the important code related issues before talking with the building department so when I do, I don't shoot myself in the foot and I already have a good idea of how its typically done. thanks for any thoughts

 

[pgrovetom]

Don’t give the state of confusion any ideas.

No.... thanks

 

[pgrovetom]

I recommend going to the bldg dpt first. But, dont quote that code stuff to them unless youre certain it helps you. Let them decide. I live in Placer County and had several questions about installing roof top solar last year. Did a walk in at the bldg dept with a hand drawing of the roof top solar. They were very nice, helpful and even allowed some deviation from the fire dept setbacks rules.

I'm also considering helping a friend build a new system based on a ground mount similar to mine but with a Hybrid Inverter and Batteries in the garage. I also read that this situation may not need rapid shutdown. Is that true or do they allow a DC disconnect at the house entry point, either manual or automatic. It would seem that this case is like the utility power, gas etc... where the fire fighters kill a main breaker or gas valve at the home entry. Since almost all the DC string power is 24" in conduit underground and only arises to enter the home at one point, wouldn't a DC disconnect that's manual or automatic work in that case. No rooftop. I'm trying to learn most of the important code related issues before talking with the building department so when I do, I don't shoot myself in the foot and I already have a good idea of how its typically done. thanks for any thoughts

I'm trying to get as much info as possible before I go to the building department just so I don't shoot myself in the foot. I would like to approach them once I think I have a code compliant design to minimize their getting overly involved and possibly making things worse. I've had that experience with the building department before both on solar and regular building. Its my experience that some plan checkers and inspectors like to make it difficult while other are easy going. Once I have a good design, show them and file for a permit and plan check and its approved, its harder for them to come back and change their minds.

 

[FilterGuy]

Thanks. That's how I read it. I'm also considering helping a friend build a new system based on a ground mount similar to mine but with a Hybrid Inverter and Batteries in the garage. I also read that this situation may not need rapid shutdown. Is that true or do they allow a DC disconnect at the house entry point, either manual or automatic. It would seem that this case is like the utility power, gas etc... where the fire fighters kill a main breaker or gas valve at the home entry. Since almost all the DC string power is 24" in conduit underground and only arises to enter the home at one point, wouldn't a DC disconnect that's manual or automatic work in that case. No rooftop. I'm trying to learn most of the important code related issues before talking with the building department so when I do, I don't shoot myself in the foot and I already have a good idea of how its typically done. thanks for any thoughts

The rapid disconnect is required for roof mount, but is not typically required for ground mount.

However, you do want to pick an inverter that has Arc-fault detection and shut-down. If the wiring is going into the house from the array, you are pretty much required to have it.

The other thing to watch for on battery systems is rapid inverter shutdown. A lot of ASJs require a rapid shutdown of the inverter so it does not continue to feed the AC after a first responder cuts the grid input. Most decent hybrid inverters have this... but check to be sure. (I am sure the EG4 hybrids have it. They can even shut down the batteries.

 

[zanydroid]

The rapid disconnect is required for roof mount, but is not typically required for ground mount.

However, you do want to pick an inverter that has Arc-fault detection and shut-down. If the wiring is going into the house from the array, you are pretty much required to have it.

Is arc fault needed for solar that does not cross into the building? IE DC terminates on an inverter that is mounted on an exterior wall.

The other thing to watch for on battery systems is rapid inverter shutdown. A lot of ASJs require a rapid shutdown of the inverter so it does not continue to feed the AC after a first responder cuts the grid input. Most decent hybrid inverters have this... but check to be sure. (I am sure the EG4 hybrids have it. They can even shut down the batteries.

How does the hybrid distinguish between power outage and first responder cutting grid input? Would it not be simpler to only do this in response to emergency shutdown button being pressed?

 

[FilterGuy]

Is arc fault needed for solar that does not cross into the building? IE DC terminates on an inverter that is mounted on an exterior wall.

I *think* it is OK as long as the PV lines are in metal conduit..... But I can't say for sure. My copy of the NEC is at home so I can't look up the details.

 

[FilterGuy]

How does the hybrid distinguish between power outage and first responder cutting grid input? Would it not be simpler to only do this in response to emergency shutdown button being pressed?

Sorry, I might have created confusion. The rapid inverter/ESS shut down is triggered by the built-in or external rapid shutdown button.

For most decent Hybrid inverters, the rapid shutdown initiator will turn off AC output as well as trigger the PV rapid shutdown.

 

[zanydroid]

I *think* it is OK as long as the PV lines are in metal conduit..... But I can't say for sure. My copy of the NEC is at home so I can't look up the details.

In my head I think AFCI is needed if the array is on the roof (and with all that exposed DC cable rawdogging it under the array, it makes sense).

While for a ground mount, if all the DC that touches a structure is contained, I don’t think the AFCI is adding value

 

[wpns]

How does the hybrid distinguish between power outage and first responder cutting grid input? Would it not be simpler to only do this in response to emergency shutdown button being pressed?

This is indeed how it works. My external button shuts down:

Inverter
Tigo boxes on rooftop solar panels (ground mount coming RSN)
Batteries
Battery breakers.

It's actually a lot of work to turn things back on, you need to reset the emergency stop button, pull the covers off both sides of the batteries (yes, I screwed the covers on), reset the battery breakers, turn the batteries on, then turn the inverter on, etc.

 

[zanydroid]

It's actually a lot of work to turn things back on, you need to reset the emergency stop button, pull the covers off both sides of the batteries (yes, I screwed the covers on), reset the battery breakers, turn the batteries on, then turn the inverter on, etc.

Ouch. I guess you have to document this in case you become incapacitated

How often do you need to emergency stop?

 

[wpns]

Ouch. I guess you have to document this in case you become incapacitated

Indeed, my wife is anxious to learn about the operation of the system from the clear documentation (I have not yet generated), including the virtual transfer switch to allow operation from the grid in case anything goes wrong.

How often do you need to emergency stop?

Only ever done it once to test the switch. Hope to never do it again for real, but you never know.

 

[Hedges]

The rapid disconnect is required for roof mount, but is not typically required for ground mount.

I *think* it is OK as long as the PV lines are in metal conduit..... But I can't say for sure. My copy of the NEC is at home so I can't look up the details.

I think the words for RSD say if PV wires are on the building (no exception named for metal conduit) then RSD required.
I think a ground mount PV array with wires coming up in conduit to inverter on wall of house requires RSD, which could be simply a safety switch isolating 600V of array from inverter. And inverter discharging its capacitors.

I think if inverter on a post one foot away from house, with only AC wires going to house, RSD not required.

I would like PV DC in metal conduit and in inverter itself exempt, but not clear it is.
Will put neighbor's inverter on his ground mount to eliminate the issue.

 

[FilterGuy]

I think the words for RSD say if PV wires are on the building (no exception named for metal conduit) then RSD required.
I think a ground mount PV array with wires coming up in conduit to inverter on wall of house requires RSD, which could be simply a safety switch isolating 600V of array from inverter. And inverter discharging its capacitors.

I think if inverter on a post one foot away from house, with only AC wires going to house, RSD not required.

I would like PV DC in metal conduit and in inverter itself exempt, but not clear it is.
Will put neighbor's inverter on his ground mount to eliminate the issue.

I was talking about the Arc Fault requirements, not RSD. Do you know the Arc Fault requirements for a ground mount array?

 

[Hedges]

"2011 NEC requires series arc-fault protection in PV installations on or penetrating a building above 80 V"

https://energy.sandia.gov/wp-content/gallery/uploads/WREF_Arc-Fault_Forum_Johnson_SAND2012-3097C.pdf

Seemed to include wires on building coming from ground mount array, but this one (2023 so current) clarifies not if in metal conduit:

"PV system dc circuits, on or in a building, operating at 80 Vdc or greater must be protected by a listed PV arc-fault circuit interrupter or other component listed to provide equivalent protection [690.11].

Arc fault protection is not required for PV system dc circuits in metal raceways, metal-clad cables, enclosed metal cable trays, or underground if they meet either exception condition in 690.11 Exception."

Solar, Part 2, based on the 2023 NEC

Solar, Part 2 Maximum PV System Direct-Current Circuit Voltage The maximum PV system direct-current circuit voltage is limited to 1000V for multifamily, commercial, and industrial buildings, and limited to 600V for one- and two-family residential buildings. You determine this voltage by one of...

www.mikeholt.com

 

[pgrovetom]

Thanks, a couple questions clarifications would be helpful.

I understand the purpose of arc-fault outlets and breakers for home AC but how and where does it work in my ground-mount array case. The array is a few hundred feet from the house and the wires enter the house from an underground conduit and travel under the house to the garage where the hybrid inverter/battery system is installed in the garage just inside the utility meter location. The meter would have AC disconnect switch followed by a transfer switch between the meter and hybrid inverter AC grid input. The AC switch is the obvious way to disconnect the whole home from the utility. The transfer switch would allow switching the home back to a pure utility home in the case the hybrid inverter fails or must be changed or have its firmware upgraded. The home 100A panel would be upgraded to a new 200 A panel and be tied to the inverter AC output. This panel would contain arc-fault breakers in the locations required by the NEC.

That leaves the DC string wires coming in from the ground mount array. Do they need a DC arc-fault interrupter at the home entry? Would this be simply a combiner box with this function integrated located at the array or at the home entry point where the conduit comes up from underground and crosses into the home? If it was at the home entry point it would also conveniently located where a rapid shutdown device might be implemented. If the Rapid Shutdown ( if actually required for this case) were at the array, it would be difficult for the firefighter to find it. If its at the home entry with a big red solar shutdown sign, its easy to find and activate.

I presume the purpose of a Rapid Shutdown function is to easily and obviously allow a firefighter or first responder to shut down immediately any conductor in the building that could pose a risk to them. Prior to roof mounted solar and or AC or DC wiring, they simply found the utility entry point and shut the main breaker or switch and turned the gas off. Now they need to find the location(s) of any shutdown switches that would cut power coming down from a roof mounted solar whether its AC or DC. Or if required, find where the DC string wires have their shutdown.

It appears my case does not require rapid shutdown at the DC string wire home entry as per the Mike Holt forum post you listed.

Solar, Part 2, based on the 2023 NEC

Solar, Part 2 Maximum PV System Direct-Current Circuit Voltage The maximum PV system direct-current circuit voltage is limited to 1000V for multifamily, commercial, and industrial buildings, and limited to 600V for one- and two-family residential buildings. You determine this voltage by one of...

www.mikeholt.com

description:


Two exceptions to the mandatory rapid shutdown function exist:

Ex 1: A rapid shutdown function is not required for ground-mounted PV system conductors that enter buildings whose sole purpose is to house PV system equipment.

Ex 2: PV equipment and circuits installed on nonenclosed detached structures including, but not limited to, parking shade structures, carports, solar trellises, and similar structures are not required to comply with the rapid shutdown requirements of 690.12.

A building with a rapid shutdown function must have a permanent label indicating the location of all rapid shutdown initiation devices. It must be near the service equipment or at an approved readily visible location [690.12(D)] and meet the specifications of 690.12.

thoughts appreciated

 

[wpns]

That leaves the DC string wires coming in from the ground mount array. Do they need a DC arc-fault interrupter at the home entry?

That's between you and your AHJ. I'm upgrading my ground mount to RSD with Tigo boxes for personal safety reasons, but that's just me, I was impressed with how easily they installed on the roof, and I need to clean up the wiring on my ground mount anyway, so it's cheap insurance against having someone die.

The arc-fault and ground-fault stuff is different, that's if your array has a problem, should your inverter shut down the array? Again, that's between you and your AHJ. In my case that's an optional function built into the inverter (EG4 18Kpv), but I don't know that I've ever seen it as a separate box for PV wiring. In my case, because of the risk of false-positive trips due to nearby lightning strikes, I've left it _off_ while I'm not in residence, but will probably enable it once I'm comfortable with the operation of the system without it, and when I'm around to fix nuisance trips.

The RSD stuff is also between you and your AHJ. Obviously you want to put it in a location where it's easily visible and easily operable by your fire dept, without being a nuisance magnet for teenagers walking by on the street. A single pushbutton (I used https://www.amazon.com/gp/product/B0BL34P2NT) that does everything (shut down the individual panels so they don't produce more than 0.6 volts each, turn off the inverter, trip the battery breakers, and shut down the BMS on each battery) may suffice. We've heard horror stories here about AHJ requiring DC battery shutoffs on the outside of the building and other silly stuff, but they are the AHJ, so you have to work with them.

 

[Hedges]

RSD is for fireman safety, apparently applies to all HV DC in or on the dwelling, even if inside metal conduit.
Only way I see around that is to have PV DC wires terminate at MPPT device not on dwelling.
Or, a disconnect not on dwelling. Could be remote trip DC breaker to put control within 10' of meter.

Arc fault is to prevent fires. Does the code exempt inside metal conduit? PV arc would likely burn through EMT. Connections are the primary concern.
Again, if DC terminates at a device not on the dwelling, that gets around it. See if conduit gives exemption.

My new install will be on dwelling roof.
I'm using a 3-pole AC switch, with 3rd pole shutting off anything that doesn't turn off when AC goes away (e.g. backup system vs. straight grid tie.)

 

[Brucey]

RSD is for fireman safety, apparently applies to all HV DC in or on the dwelling, even if inside metal conduit.
Only way I see around that is to have PV DC wires terminate at MPPT device not on dwelling.
Or, a disconnect not on dwelling. Could be remote trip DC breaker to put control within 10' of meter.

Arc fault is to prevent fires. Does the code exempt inside metal conduit? PV arc would likely burn through EMT. Connections are the primary concern.
Again, if DC terminates at a device not on the dwelling, that gets around it. See if conduit gives exemption.

My new install will be on dwelling roof.
I'm using a 3-pole AC switch, with 3rd pole shutting off anything that doesn't turn off when AC goes away (e.g. backup system vs. straight grid tie.)

My understanding is PV in conduit is an exemption to the arc fault etc requirements if it's coming up the side of a dwelling from a ground mount for example. For roof on a dwelling you'll prob need ground fault, arc fault, and rapid shutdown. The arc fault is for the PV, not the inverter side if I'm not mistaken..

 

[Brucey]

Post in thread 'Need To Add Arc Fault Detection to system' https://diysolarforum.com/threads/need-to-add-arc-fault-detection-to-system.61077/post-757403

 

[zanydroid]

That leaves the DC string wires coming in from the ground mount array. Do they need a DC arc-fault interrupter at the home entry? Would this be simply a combiner box with this function integrated located at the array or at the home entry point where the conduit comes up from underground and crosses into the home? If it was at the home entry point it would also conveniently located where a rapid shutdown device might be implemented. If the Rapid Shutdown ( if actually required for this case) were at the array, it would be difficult for the firefighter to find it. If its at the home entry with a big red solar shutdown sign, its easy to find and activate.

Rapid shutdown is not needed for ground mount except for the edge case of the riser at the building touching the building. I believe you found the references for that. Typically rapid shutdown is triggered by switch next to or on the inverter.

Arc fault is handled by the MPPT. Most listed MPPTs in the US (with the exception of like Victron MPPTs and hybrid heat pump MPPTs) have AFCI. Other wise it would be too painful for installers to use in residential projects.

Arc fault protections on MPPTs also don't really disconnect the solar panels at the source. Instead, they detect a problem and either raise an alarm or disable the circuit at the load side. Unloading is enough to address series faults within a single conductor but less likely to stop parallel faults between conductors/circuits.