Rapid Shut Down question

[donb108]

As I mentioned in another thread, I have an existing solar system with panels on a shed roof and back wall; now I'm repurposing them to a new system.

A couple years ago, when I first read about RSD, I understood it was not required on ground mounts or un-occupied structures; like sheds and garages. So, I built the shed system without any RSD equipment. Now I'm working on the new system and plan to re-wire the shed panels to connect to the new inverter.

Reading-up on the issue, it kinda looks like I may need to add RSD. Apparently, it's not required if the primary purpose of the structure is to hold panels; like a ground mount or power-house. But my shed is just a shed, used for lawn mowers and yard stuff. Do I need to add RSD?

 

[svetz]

I think Louisiana is currently on NEC 2017. Section 690.12 mandates RSD for buildings, but is a shed a building? If your system is under 30V DC no issue as the ruling is:

• Controlled conductors outside the array boundary must be reduced to less than 30 volts within 30 seconds.
• Within the array boundary, the voltage must be less than 80 volts within 30 seconds.

Small sheds often do not require building permits if they are below a certain size threshold (typically 200–400 square feet, depending on the parish). If your shed is small enough to be exempt from permitting, you may not face strict enforcement of NEC requirements for RSD, especially for a non-grid-tied, DIY off-grid system. However, if the shed requires a permit or if the solar installation is subject to inspection (e.g., due to its size or connection to your home’s electrical system), the Authority Having Jurisdiction (AHJ) may enforce NEC 690.12, including RSD.

You never know how a local interpretations by the AHJ will go. That is, if your inspector doesn't like solar or doesn't understand it they may tell you that you must have it regardless.

 

[cs1234]

That is, if your inspector doesn't like solar or doesn't understand it they may tell you that you must have it regardless.

Doesn't like solar? That's awful!

 

[donb108]

I think Louisiana is currently on NEC 2017.

I just checked, in 2021 we switched to 2020.

If your shed is small enough to be exempt from permitting,

It's 12x16 (192 sq ft), anchored on a concrete slab, and has flood vents (sheds tend to float away in S Louisiana). I got a permit and passed inspection, which gave me air-cover from the HOA.

I called the parish zoning and permitting office and asked about RSD; he gave a firm yes. I didn't argue the shed, unoccupied structure stuff, but I suspect they just want it. I don't have that many panels, so I'll probably just add it in.

 

[svetz]

It's 12x16 (192 sq ft), anchored on a concrete slab, and has flood vents (sheds tend to float away in S Louisiana). I got a permit and passed inspection, which gave me air-cover from the HOA.
I called the parish zoning and permitting office and asked about RSD; he gave a firm yes. I didn't argue the shed, unoccupied structure stuff, but I suspect they just want it. I don't have that many panels, so I'll probably just add it in.

Sometimes its CYA, sometimes it's solar is evil, sometimes it's just that they had bad coffee. ; -)
I've always chatted with them and not had any problems, but then I also see them as my last-chance to survive any bone-headed screwups I make.

690.12 was expanded in the 2020 edition, clarifying module-level vs. array-level shutdown, which might give you more flexibility.

Don't forget the labeling (690.56(C)(2), 10.21(B)), some RSDs will come with peel and stick. They can't be hand-written, but they can be stenciled (unless your inspector is feeling persnickety).

One line that might work with your inspector if you feel he wants to lean your way is "You know, in most scenarios, a shed on fire would likely burn to the ground before the fire department 5 miles away could arrive and extinguish the fire. That I'm storing gasoline for the mower just makes it even less likely to survive."

Which sadly is true, most have structural collapse in under 10 minutes and of course by the time anyone notices it's generally going pretty good.

 

[donb108]

One line that might work with your inspector if you feel he wants to lean your way is "You know, in most scenarios, a shed on fire would likely burn to the ground before the fire department 5 miles away could arrive and extinguish the fire. That I'm storing gasoline for the mower just makes it even less likely to survive."

Which sadly is true, most have structural collapse in under 10 minutes and of course by the time anyone notices it's generally going pretty good.

To say nothing of the risk to the fireman. I doubt they'd want to climb up there to save a lawn mower.

Next year I'll probably add more panels on the main house and those will surely need RSD. It occurred to me that an emergency shut down switch should probably turn off all the panels at the same time, not just some.

 

[svetz]

To say nothing of the risk to the fireman. I doubt they'd want to climb up there to save a lawn mower.

Next year I'll probably add more panels on the main house and those will surely need RSD. It occurred to me that an emergency shut down switch should probably turn off all the panels at the same time, not just some.

I have microinverters, the RSD and arc protection are built in. Really good option for scaling up. ; -)