Rapid Shutdown for Ground mount with inverter in garage

[solarken]

We use NEC 2017 in Ohio. For a ground mounted residential system I am designing, the inverter will be in an attached garage, and a DC-coupled ESS for partial home backup will be in the basement. 690.12 has requirements for Rapid Shutdown of PV Systems on buildings. The only portion of the PV System that is on a building is the portion of DC circuit conductors that will penetrate the garage wall and turn up into the inverter.

I interpret 690.12(B)(2) Inside the Array Boundary requirements as not applicable since this is a gound mount. For 690.12(B)(1) Outside the Array Boundary, it states "Controlled conductors located outside the boundary or more than 1m (3ft) from the point of entry inside a building shall be limited to not more than 30 volts within 30 seconds.

If I keep the conductor length from the inverter to the point of entry inside the building, to less than 1m, it seems that no controlled conductor would be applicable to this PV system. Am I understanding this right?

Normally I rely on the inverter output AC disconnect required by the utility to be outside accessible near the meter to meet the rapid shutdown requirement for SolarEdge systems such as this one (which would mean Rapid Shitdown comes along for free) but with the inverter configured for battery backup it seems that killing the connection to the grid will not cause the inverter to shut down the array since it will try to grid form and keep the optimizers producing, even thought the energy can't go anywhere. So I would need to add a Rapid shutdown initiation switch which is what I am trying to avoid. I also do not want to add disconnects to the three PV strings at the house because of aesthetics and cost.

Has anyone encountered this situation?

Thanks, Ken

 

[jaggedben]

You don't need to provide rapid shutdown at the array, but you do need to provide it for the DC conductors that enter the garage. I'm no longer up-to-date on Solaredge enough to advise you about specifics, but it sounds like you need the RS initiation switch, or disconnects. Or, move the inverter so that the PV DC conductors aren't in or on the garage.

 

[ggunn]

Why don't you mount the inverter at the array and avoid the issue?

 

[pv_n00b]

Since your DC conductors are outside the array boundary and not on the building you get 1 m from penetrating the building before they fall under 690.12(B)(1). I think you have it correct for the DC conductors. The AC inverter output will still fall under 690.12(B)(1) through. That's going to require a big red button on a backup system.

 

[solarken]

Since your DC conductors are outside the array boundary and not on the building you get 1 m from penetrating the building before they fall under 690.12(B)(1). I think you have it correct for the DC conductors. The AC inverter output will still fall under 690.12(B)(1) through. That's going to require a big red button on a backup system.

Thanks for response. I don't interpret 690.12 to apply to inverter output circuits unless the inverter is within the array/on the roof, like micro-inverters. The intention is to protect firefighters from high voltage within the vicinity of the array, right?

Why don't you mount the inverter at the array and avoid the issue?

Several reasons. Inverters fail more often when outside exposed to extreme weather swings (Ohio), the array is in a field pretty far from the home, so would rather run 400V DC than 240V AC for better efficiency and avoid voltage rise issues, the battery is in the basement (power and RS-485 runs), and ethernet for monitoring would be more difficult.

 

[solarken]

You don't need to provide rapid shutdown at the array, but you do need to provide it for the DC conductors that enter the garage. I'm no longer up-to-date on Solaredge enough to advise you about specifics, but it sounds like you need the RS initiation switch, or disconnects. Or, move the inverter so that the PV DC conductors aren't in or on the garage.

Doesn't the "more than 1 meter from the point of entry" specification in 690.12(B)(1) mean that DC conductors entering the garage only need to be controlled beyond 1 meter length?

 

[jaggedben]

Doesn't the "more than 1 meter from the point of entry" specification in 690.12(B)(1) mean that DC conductors entering the garage only need to be controlled beyond 1 meter length?

I don't read it that way because it's what you quoted or outside the array boundary, and your conductors are 'outside the array boundary', which is also the heading of that subsection. I believe what they had in mind was that the 1ft array boundary extends below (and above) the array but they didn't want to allow penetrating the building and running long lengths of conductors underneath the roof while still technically within the array boundary (1 foot below modules).

 

[wwhitney]

There's definitely a lack of logical parallelism between the wording in 2017 690.12(B)(1) and 690.12(B)(2)(2).

690.12(B)(2)(2) refers to "conductors located inside the boundary or not more than 1 m (3 ft) from the point of penetration of the surface of the building." That would be an inclusive or. To rephrase that as an exclusive or (xor), we'd get "inside the boundary" xor "outside the boundary but not more than 3 ft from the point of penetration".

690.12(B)(1) refers to "conductors located outside the boundary or more than 1 m (3 ft) from the point of entry inside a building." [For parallelism that should be "from the point of penetration of the surface of the building."] Rephrasing that as an xor we get "outside the boundary" xor "inside the boundary and more than 3ft from the point of penetration."

So logically, if you are outside the boundary but not more than 3ft from the point of penetration, you are subject to both 690.12(B)(1) and 690.12(B)(2)(2) (although for the latter, 690.12(B)(2) offers other options). Likewise if you are inside the boundary and more than 3ft from the point of penetration, you are also subject to both 690.12(B)(1) and 690.12(B)(2)(2) (again, other options for the latter).

I doubt this was the intention. Since the requirements of 690.12(B)(2)(2) are weaker than 690.12(B)(1) (an 80V threshold rather than a 30V threshold), I expect the intention was that the 80V threshold only apply when both inside the array boundary and [either outside the building or less than 3 ft from the point of entry]. And then the 30V requirement would apply when outside the array boundary or when [inside the the building and more than 3ft from the point of entry].

But of course that's not what the language says, as it wasn't written by a logician.

Cheers, Wayne

 

[ggunn]

There's definitely a lack of logical parallelism between the wording in 2017 690.12(B)(1) and 690.12(B)(2)(2).

690.12(B)(2)(2) refers to "conductors located inside the boundary or not more than 1 m (3 ft) from the point of penetration of the surface of the building." That would be an inclusive or. To rephrase that as an exclusive or (xor), we'd get "inside the boundary" xor "outside the boundary but not more than 3 ft from the point of penetration".

690.12(B)(1) refers to "conductors located outside the boundary or more than 1 m (3 ft) from the point of entry inside a building." [For parallelism that should be "from the point of penetration of the surface of the building."] Rephrasing that as an xor we get "outside the boundary" xor "inside the boundary and more than 3ft from the point of penetration."

So logically, if you are outside the boundary but not more than 3ft from the point of penetration, you are subject to both 690.12(B)(1) and 690.12(B)(2)(2) (although for the latter, 690.12(B)(2) offers other options). Likewise if you are inside the boundary and more than 3ft from the point of penetration, you are also subject to both 690.12(B)(1) and 690.12(B)(2)(2) (again, other options for the latter).

I doubt this was the intention. Since the requirements of 690.12(B)(2)(2) are weaker than 690.12(B)(1) (an 80V threshold rather than a 30V threshold), I expect the intention was that the 80V threshold only apply when both inside the array boundary and [either outside the building or less than 3 ft from the point of entry]. And then the 30V requirement would apply when outside the array boundary or when [inside the the building and more than 3ft from the point of entry].

But of course that's not what the language says, as it wasn't written by a logician.

Cheers, Wayne

And then UL3741 comes in and makes the water even muddier.

 

[electrofelon]

.... Inverters fail more often when outside exposed to extreme weather swings (Ohio), the array is in a field pretty far from the home, so would rather run 400V DC than 240V AC for better efficiency and avoid voltage rise issues, the battery is in the basement (power and RS-485 runs), and ethernet for monitoring would be more difficult.

Just my two cents, but I am skeptical of the weather swings argument.

Regarding the length/efficiency, my niche is actually ground mount arrays that are quite far from the house. We have done several that are 700-800 ft away. I have ran the numbers multiple times trying to get it to work, but never found it cost-effective to run DC back versus AC. Even tried it with fronius inverters which do 1000 volt strings, and it just doesn't pan out. The main factors are:

1. For DC you would typically be dealing with CU conductors (although aluminum PV wire is available), vs AL for AC.

2. You probably won't be able to get the DC voltage as high as you think unless you get lucky with the way the panel string up and/or make compromises such as skimping on your available mppts.

3. It's somewhat of a hassle pulling seven conductors versus one plexed aluminum set.

The voltage drop/rise issue certainly favors the DC run, but you're really only looking at about a three volt difference and if you are up that high where that 3-volts breaks the camel's back, you've probably got other issues, like a bad utility voltage regulator.

 

[BackCountry]

Just my two cents, but I am skeptical of the weather swings argument.

Regarding the length/efficiency, my niche is actually ground mount arrays that are quite far from the house. We have done several that are 700-800 ft away. I have ran the numbers multiple times trying to get it to work, but never found it cost-effective to run DC back versus AC. Even tried it with fronius inverters which do 1000 volt strings, and it just doesn't pan out. The main factors are:

1. For DC you would typically be dealing with CU conductors (although aluminum PV wire is available), vs AL for AC.

2. You probably won't be able to get the DC voltage as high as you think unless you get lucky with the way the panel string up and/or make compromises such as skimping on your available mppts.

3. It's somewhat of a hassle pulling seven conductors versus one plexed aluminum set.

The voltage drop/rise issue certainly favors the DC run, but you're really only looking at about a three volt difference and if you are up that high where that 3-volts breaks the camel's back, you've probably got other issues, like a bad utility voltage regulator.

I’ve done many ground mounts that were far away also, we almost specialize in it.

We’ve calc’d that using DC makes better sense because of voltage drop.

For example, on a 24kw ground mount with three SMA 7.7 inverters, our net backfeed is somewhere around 125a. Our string voltage regularly metered in the low 400’s, which calc’s to #8’s for the DC side. So we pulled 6 sets of #8 CU and a ground in 1-1/2” conduit.

If we’d done the AC side with AL, we’re looking at 3” conduit with 500KCMil.

My material cost would be significantly higher, not to mention we like to have network connectivity nearby.

As far as rapid shutdown — I think this is a non issue as long as your DC conductors land as soon as possible once penetrating the building. Hopefully you’re not using SolarEdge for obvious reasons.

 

[electrofelon]

I am s

I’ve done many ground mounts that were far away also, we almost specialize in it.

We’ve calc’d that using DC makes better sense because of voltage drop.

For example, on a 24kw ground mount with three SMA 7.7 inverters, our net backfeed is somewhere around 125a. Our string voltage regularly metered in the low 400’s, which calc’s to #8’s for the DC side. So we pulled 6 sets of #8 CU and a ground in 1-1/2” conduit.

If we’d done the AC side with AL, we’re looking at 3” conduit with 500KCMil.

My material cost would be significantly higher, not to mention we like to have network connectivity nearby.

As far as rapid shutdown — I think this is a non issue as long as your DC conductors land as soon as possible once penetrating the building. Hopefully you’re not using SolarEdge for obvious reasons.

I am skeptical, and you will have to give me more specifics . So are you sending 9 strings back? How far? #8 is say .50/ft so 9 strings is $9/ ft plus EGC. I run service conductors out to the array using 230.40 exception #3 so only 3 wires and a minimum sized neutral. One we did was I think 700 feet and we used 500-500-1/0 in 2.5" PVC. It definitely beat running strings back. Also how are you getting 125A for 3 7.7's? I get 96 amps.

 

[BackCountry]

I am s
I am skeptical, and you will have to give me more specifics . So are you sending 9 strings back? How far? #8 is say .50/ft so 9 strings is $9/ ft plus EGC. I run service conductors out to the array using 230.40 exception #3 so only 3 wires and a minimum sized neutral. One we did was I think 700 feet and we used 500-500-1/0 in 2.5" PVC. It definitely beat running strings back. Also how are you getting 125A for 3 7.7's? I get 96 amps.

You’re probably more code dialed than I am on that EGC exception, we outside our designs and just do whatever the EE says. 125A is based on 32*3 = 96A, so then we size up from there at 80% loading.

I was sending 6 strings back, two per inverter. 64 QCell 430’s.

We have a little pallet set up for the skid steer that holds all 13 reels of #8.

My cost on 1.5” versus 2.5” conduit is significantly less, and the other thing is I don’t have to deal with voltage rise being out of spec with the grid profile on the AC side, which I’ve ran into more than once.

Large single phase ground mounts are tricky, I always try to take advantage of the DC higher voltage and cluster our inverters at the service.

 

[pv_n00b]

Thanks for response. I don't interpret 690.12 to apply to inverter output circuits unless the inverter is within the array/on the roof, like micro-inverters. The intention is to protect firefighters from high voltage within the vicinity of the array, right?

Inverter AC output circuits are controlled conductors under RSD since 690.12 does not limit RSD to DC conductors. They have to comply with either the inside or outside array RSD requirements.

 

[pv_n00b]

Doesn't the "more than 1 meter from the point of entry" specification in 690.12(B)(1) mean that DC conductors entering the garage only need to be controlled beyond 1 meter length?

That's my reading of it, although it's not limited to DC conductors. You get a 1m grace length. But if you are running 50m inside a building your need to have RSD. This only comes up if you have an otherwise excluded system with no RSD, like a ground mount, that has circuits that penetrate a building. If it's a roof-mounted system then the conductors will already be under RSD when they get to the building penetration and that RSD protection continues once the conductors are inside. The 1m allowance does not buy anything extra.

 

[jaggedben]

The 2020 NEC clarifies that inverter output circuits are only covered within the array boundary.

It seems like a distinction without a difference when the service disconnect is the intiation device.

 

[ggunn]

Inverter AC output circuits are controlled conductors under RSD since 690.12 does not limit RSD to DC conductors. They have to comply with either the inside or outside array RSD requirements.

Well, OK, but don't they comply by default? Do AC inverter output conductors retain any DC voltage when power from the utility is interrupted? I would not think so.

 

[jaggedben]

Well, OK, but don't they comply by default? Do AC inverter output conductors retain any DC voltage when power from the utility is interrupted? I would not think so.

It depends how Rapid Shutdown is initiated. Not all systems use AC shutdown to initiate.

And also, as I stated above, in the 2020 NEC this is no longer an issue.

 

[electrofelon]

You’re probably more code dialed than I am on that EGC exception, we outside our designs and just do whatever the EE says. 125A is based on 32*3 = 96A, so then we size up from there at 80% loading.

I was sending 6 strings back, two per inverter. 64 QCell 430’s.

We have a little pallet set up for the skid steer that holds all 13 reels of #8.

My cost on 1.5” versus 2.5” conduit is significantly less, and the other thing is I don’t have to deal with voltage rise being out of spec with the grid profile on the AC side, which I’ve ran into more than once.

Large single phase ground mounts are tricky, I always try to take advantage of the DC higher voltage and cluster our inverters at the service.

Just make sure to not have the extra 25% figured in for voltage drop purposes. Anyway I have always found it more cost effective to run AC. We don't have to compromise on string quantity and would typically use all 9 (on a 3 7.7 system). Typically we are about 3 volts drop, and again, if you are getting up high enough to trip the inverters, I'll bet you have other problems and would have them even with a perfect conductor. Yes conduit is extremely expensive right now so that is a factor of course. My AC conductors are USE so I often use lesser cost protection methods such as 4" SDR 35 pipe (if I need something big) which is the same cost as 2" PVC. Anyway we apparently both have our system and have it dialed in and for me I find running AC to be simpler and more cost effective.

 

[BackCountry]

Just make sure to not have the extra 25% figured in for voltage drop purposes. Anyway I have always found it more cost effective to run AC. We don't have to compromise on string quantity and would typically use all 9 (on a 3 7.7 system). Typically we are about 3 volts drop, and again, if you are getting up high enough to trip the inverters, I'll bet you have other problems and would have them even with a perfect conductor. Yes conduit is extremely expensive right now so that is a factor of course. My AC conductors are USE so I often use lesser cost protection methods such as 4" SDR 35 pipe (if I need something big) which is the same cost as 2" PVC. Anyway we apparently both have our system and have it dialed in and for me I find running AC to be simpler and more cost effective.

What we need to do is have an electrician exchange program where we all work for each other and learn each other’s secrets. Now that would be helpful! I learn a lot from here.

My go to single phase package is Unirac GFT with SMA 7.7’s. The single biggest problem I have with those is wifi connectivity, so no more using wifi with them — they are terrible. Ethernet only to a switch with a wifi bridge, I include that in our bids now.