NEC 2017 and RSS - I feel so blessed

aksala · July 2018

So I'm working on getting an off-grid home built in Alaska. It's not a cabin or a DIY homestead. It's a house by a custom builder that just happens to have to be off-grid. The builder builds to code, which is great, but this is their first off-grid home, so we're all learning some things as we go. One of those things is what the electrical inspectors will want to see for code compliance with regards to my PV installation.

Today I get word that after a meeting of the inspectors and some other knowledgeable folks within the State of Alaska including at least my electrical contractor, the inspectors have decided they are going to inspect against the 2017 NEC code as it has been adopted by the state. Yay me!

So as I understand it, that now requires my intended roof mounted array to include the remote disconnects within the array itself to limit voltage on the wires to less than 80V within the array. At 30 panels that's a lot of little gizmos to have to add to the system. I wager I may be one of the first in this forum to have to deal with this on a residential install. I can't say as I'm at all happy about it and I'm not sure if I can get around it with a ground mount array or whether I want to do a ground mount array. I didn't really want to before, as the roof was already there, making a great support for 30 panels and it's already up off the ground to get a little more sun in the late fall and early spring.

Does anyone know if the new 2017 NEC RSS options apply equally to ground mount vs's roof mount arrays? Perhaps I'll just start with a much smaller array on the roof and then come back and add ground mount panels after the inspectors are done and gone.

Photowhit · July 2018

Isn't this just a box at ground level that has wires from each string of panels on the roof? and a single shut off? Something like this;
https://www.solar-electric.com/lib/wind-sun/MNdiscos_all_frontBack.pdf

mcgivor · July 2018

The changes appear to be for roof mounted arrays for fire related access, this article covers the changes. Hope this helps. https://www.civicsolar.com/support/installer/articles/changes-article-690-nec-2017

aksala · July 2018

@Photowhit, not any longer. That was 2014, this is 2017! It's crazy if you ask me. The code requires voltage to be kept to less than 80V on the wires within the PV array once RSS has been initiated, and wires from the array to the inverter to less than 30V within 30 seconds of RSS activation.

mike95490 · July 2018

There is a brand of inverter that has "Optimizers" at each panel or pair of panels, that shuts the system down when commanded. I don't know if they work for off-grid.

littleharbor2 · July 2018

Tigo may have what you need.
https://www.tigoenergy.com/about-tigo/press-releases/52/

Photowhit · July 2018

aksala said:

@Photowhit, not any longer. That was 2014, this is 2017! It's crazy if you ask me. The code requires voltage to be kept to less than 80V on the wires within the PV array once RSS has been initiated, and wires from the array to the inverter to less than 30V within 30 seconds of RSS activation.

Not sue why you think a complete disconnection won't bring the voltage down to '0'. Solar panels are a loop, is they aren't connected there is no voltage. The inverter might have some very small storage in capacitors, but pretty much instant as well. It would be 2 breakers, one for the solar array and one for a battery to the inverter. Are you saying a single switch must do both, disconnect the array and the inverter?

BB. · July 2018

I think they want less than 80 volts on any point in the array itself when shut down (Voc=<80 volts?).

Since it is not uncommon to have anywhere from 100 to >500 volts from series connected solar panels (central GT inverters, any >100 VDC Vpanel input charge controllers)--You are left with some hokey disconnect every two panels, or (on quick skim) all of the solar cables must be in metal conduit(?) and "master disconnect" on roof (?).

Not sure and have not delved into the changes in new NEC...

Probably would be nice to have a NEC 2017+ thread to discuss the details or just continue the discussion in this thread (if OK with Akasala).

-Bill

aksala · July 2018

BB. said:

I think they want less than 80 volts on any point in the array itself when shut down (Voc=<80 volts?).

Since it is not uncommon to have anywhere from 100 to >500 volts from series connected solar panels (central GT inverters, any >100 VDC Vpanel input charge controllers)--You are left with some hokey disconnect every two panels, or (on quick skim) all of the solar cables must be in metal conduit(?) and "master disconnect" on roof (?).

Not sure and have not delved into the changes in new NEC...

Probably would be nice to have a NEC 2017+ thread to discuss the details or just continue the discussion in this thread (if OK with Akasala).

-Bill

Exactly Bill. I wondered if I could get away with an every other panel disconnect if I absolutely have to go that route. And I have no problem if you want to rename this thread and continue. It's rather crazy since at first I was told that my GC and his Electrical Sub wanted to check with the AHJ to see what they would be looking for. That turned into, "Gee, we're not sure. We'll have a meeting to figure it out." That led to my GC telling me that they said they intend to inspect to the 2017 NEC code as adopted.

Fast forward to today. I get a revised quote from a vendor in Alaska which now is supposed to include the RSS equipment. Instead of addressing 2017 code, it lists a birdhouse and the related remote combiner/disconnect from Midnight. I send an email to my GC to say that is 2014 compliant, but not 2017. His response is along the lines of, well often the inspectors only go after the intent for fire and safety and he's leaving it to the Electrical Sub to see if anything additional is needed. I'm just keeping my mouth shut for now.

BB. · July 2018

Generally, the inspectors cannot inspect to a code that has not been adopted by "their agency"...

I don't know how it works in your area--But in my area inspectors are not liable for their inspections or their recommendations/requirements. And have been known to gloss over major issues (like gray market solar panels that did not have UL/NRTL markings) or even if their requirements are wrong/dangerous:

http://forum.solar-electric.com/discussion/3375/panel-fire-question/p1
http://midniteftp.com/forum/index.php?topic=142.0
http://forum.solar-electric.com/discussion/9345/system-grounding/p1 (related to midnite thread)

See if you can work with them ahead of times and get pre-approved plans (to whatever NEC code) that make sense to you and your installer.

For my area, the best usage for the inspectors is to point out real concerns you may have with installer/materials/other issues. And let them "enforce" what you think is best with your contractors/installers.

-Bill

Photowhit · July 2018

BB. said:

I think they want less than 80 volts on any point in the array itself when shut down (Voc=<80 volts?).

So they want no potential?

Without a loop/closed circuit there is no measurable voltage.

mcgivor · July 2018

There's VOC on an open circuit, so any more than 2 GT panels, more or less, will exceed 80V. The problem could be solved using DC rated relays to interrupt each pair, or individual panels in a series string where the voltage exceeds 40V, thereby satisfying code requirements, it's a major PITA having to add all this complexity to what would be a relatively simple installation. Sometimes it's better to ask for forgiveness rather than permission, but understandably you wanted to adhere to current regulations. Attached is a pdf with relays designed for the purpose, Omron make quality controls equipment which I've used extensively in the trade.

aksala · July 2018

I found this informative video on Midnight's site. It's mostly about the 2014 rules and how to use the Birdhouse and Remote Disconnects and breakers, and it's good info. But for 2017 just fast forward to 45:20 and start watching.

https://www.youtube.com/watch?time_continue=296&v=SSYSUerLGUU

Dave Angelini · July 2018

Having done quite a few homes in Alaska I am surprised by your problems.
Most homes offgrid are built to code and wired for AC power. They are tested for the certificate of occupancy with a generator running.
There is zero DC wiring except to the batteries and from the disconnect outside the building.
As Bill said very few AHJ's are up to 2017 and for Offgrid most do not care as long your "people" did not make an issue of this.

But, there are exceptions and you will have to do what they want and if it is really stupid and mindless, fix it later. Good Luck!

Dave Angelini · July 2018

One of my solar wrench buddies had to do this below. Is your power system in non-habitable space?

The really bad news is they are working on 2020 right now

You will have to undo some what they make you do as 2017 opens new ways to lose offgrid power and you get to come home to spoiled food in your refrigerator. Yuk

I believe there was a big improvement for off-grid systems as relates to RS
in the 2017 NEC - the diagrams in 690.1(b) all show the PV system
disconnect clearly now.  If you check out the diagrams you can see that
energy storage/battery circuits, including the battery-based inverter
whether AC or DC coupled, are outside the PV system boundary, thus not PV
system circuits, thus not subject to RS.

 I agree with you, Ray, as a purely off-grid solar installer and
 troubleshooter. I think all that was accomplished in NEC 2017 on this issue
 is that non-habitable structures, like the common off-grid 'power shed'
 don't need 690.12 RS anymore.

aksala · July 2018

Dave Angelini said:

Having done quite a few homes in Alaska I am surprised by your problems.
Most homes offgrid are built to code and wired for AC power. They are tested for the certificate of occupancy with a generator running.
There is zero DC wiring except to the batteries and from the disconnect outside the building.
As Bill said very few AHJ's are up to 2017 and for Offgrid most do not care as long your "people" did not make an issue of this.

But, there are exceptions and you will have to do what they want and if it is really stupid and mindless, fix it later. Good Luck!

I was surprised as well Dave, and I believe it was made an issue only in that the Electrician wanted to know what the inspector is looking for. That prompted the inspector to ask for a meeting with their peers to go over the recent code revisions. Since the 2017 RSS stuff goes into effect January 2019, we may just be able to play the birdhouse game at 2014 code. This is Mat-Su borough, so if you do any future work in that borough and it's done to code, beware.

And FWIW, the thought had already crossed my mind that we could just wire up the 6848 and the battery bank and generator and call it good. I could then do the solar later after we occupy.

Dave Angelini · July 2018

Yes or just use a generator. Whatever they want they get! Then they leave and that is a good thing also.

I sent you a private message.

t00ls · January 2019

just curious....if the home is off grid...why is there an electrical inspector

if I build a house here in kentucky and I'm not connecting to the grid, I could care less about an inspector....they have no business being there...because I am not connecting to the grid

mcgivor · January 2019

t00ls said:

just curious....if the home is off grid...why is there an electrical inspector

if I build a house here in kentucky and I'm not connecting to the grid, I could care less about an inspector....they have no business being there...because I am not connecting to the grid

Perhaps home insurance will have a problem paying out should there be a claim, particularly if fire is involved.

BB. · January 2019

Some regions simply require code for even off grid homes.

One was really funny require was posted here years ago, Their inspectors even required a utility meter socket for a solar powered off grid home (confused some people seeing an empty meter socket and they had AC power at the cabin).

-Bill

t00ls · January 2019

mcgivor said:

t00ls said:

just curious....if the home is off grid...why is there an electrical inspector

if I build a house here in kentucky and I'm not connecting to the grid, I could care less about an inspector....they have no business being there...because I am not connecting to the grid

Perhaps home insurance will have a problem paying out should there be a claim, particularly if fire is involved.

and that makes sense....dont do homeowners insurance myself......I also know that whatever I have done....surpasses any safety requirements the NEC has...meaning my stuff wont catch anything on fire

but this module level shutdown has got to be the stupidest things the NEC has come up with yet,, if everything is in conduit and junction boxes on the roof.....and you have a combiner box with breakers to disconnect your up to 600v connections from the rest of the system....I dont see the problem

because once the circuit is open , it is only potential.....a potential that doesnt have a way to become a circuit...maybe I'm missing the intent

MrM1 · January 2019

I guess the intent - as I have read it - about module level (or every panel) shutdown has to do with the safety of firemen (oh oops firepersons) in case of fire. If they have to come thru the roof at the location of the panels and cut thru the panels. But I have also read where fire chiefs tell their departments to stay away from panels all together. So yes ... I think module level shut down (every panel) is pretty stupid.

littleharbor2 · January 2019

MrM1 said:

I guess the intent - as I have read it - about module level (or every panel) shutdown has to do with the safety of firemen (oh oops firepersons) in case of fire. If they have to come thru the roof at the location of the panels and cut thru the panels. But I have also read where fire chiefs tell their departments to stay away from panels all together. So yes ... I think module level shut down (every panel) is pretty stupid.

Firefighters aren't going to be cutting through the ceiling to get up onto the roof. What they need to do is cut through the roof from above to ventilate the attics. This is firefighting 101. When panels are series wired for voltages up to 1000 volts even if the circuit has been opened elsewhere they would risk cutting through conduit and creating a complete circuit with their tools. These, potentially deadly, high voltages wouldn't be present with panel level shutdown.

MrM1 · January 2019

That is what I am talking about. Cutting thru the roof not going up from the bottom. But I have read a good deal about this debate from firefighters, including what seems to be the origin, and there seems to be debate as to the necessity of it.

MrM1 · January 2019

I just think the 2017 NEC is heavy handed. Perhaps not on large commercial higher voltage systems, but on smaller home and off grid systems. This is some of my reading...

https://www.renewableenergyworld.com/ugc/articles/2015/09/solar-rapid-shutdown--will-it-shut-you-out.html

https://solarprofessional.com/articles/design-installation/rapid-shutdown-for-pv-systems/page/0/2#.XDp4H817nIU

littleharbor2 · January 2019

MrM1 said:

I just think the 2017 NEC is heavy handed. Perhaps not on large commercial higher voltage systems, but on smaller home and off grid systems. This is some of my reading...

https://www.renewableenergyworld.com/ugc/articles/2015/09/solar-rapid-shutdown--will-it-shut-you-out.html

https://solarprofessional.com/articles/design-installation/rapid-shutdown-for-pv-systems/page/0/2#.XDp4H817nIU

Just read the first article. Many good points made there. The intent of rapid shutdown regulations are safety based, which I'm sure we're all for. This article does bring to light issues I hadn't considered though, namely, will it work when it is supposed to. I never would imagine a firefighter trying to smash through an array for any reason and wisely they have been trained to expect these solar circuits to be live regardless whether they are or not.

rollandelliott · July 2019

https://www.sma-america.com/products/smart-module-technology/ts4-r-module-technology.html
sma has micro inverters that address this.

Dave Angelini · July 2019

Design offgrid solar systems to not use the roof. Problem solved by old hippies 35 years ago....

rollandelliott · July 2019

SMA Rapid Shutdown Box RSB-2S-US-10
So this box with buttons to disconnect the DC solar array costs $250 more.

I do not understand how this makes a solar array more safe for emergency workers? if they cut through 300v pc wire on the roof, they are still going to get shocked right? Unless the box with put in the middle of an 8 panel string, but that would onlyu reduce the voltage by half so still not really safe??

billybob9 · July 2019

SMA Rapid Shutdown Box RSB-2S-US-10 has a real problem. This is because it is being installed on the roof under the last solar panel in the array. It can also be installed on the side of the house but most installs seam to be roof top. After reviewing many YouTube DIYs and seeing that sometimes the DC shut down DOES NOT SHUTDOWN on one string I opened my NEW SMA rapid shutdown box and saw 2 Relays. The electronic board with these 2 relays would be about 3 inches from the red hot panels if installed on the roof. Relays are mechanical so over time I believe these would jam up (under these conditions). People that were having these problems were about 4 year users. So who wants to get a contract with SMA to reinstall every Rapid Shutdown box on the roof since 2014.

rollandelliott · July 2019

not me, lol. I hate working on hot roofs. So is there a better product? to comply within 1 feet of code, installers really do not have much of a choice but to put on roofs. east side of house would be best, but probabaly less then 20% have all the stars aligned to do that. Maybe installers should be putting an opened ended (for air flow) aluminum piece of sheet metal over it to shade it, but I'm sure that would violate code some how.

NEC 2017 and RSS - I feel so blessed

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