E-Stops and 2023 690.13(E)

[TallTimber]

I may have a little bit of a misunderstanding of Rapid shutdown. I was under the impression that rapid shutdown is a "stop generating" command via the RSD. Does this RSD also disconnect the ungrounded conductors? It seems like the RSD alone would not satisfy 2023 690.13(E). Maybe I am missing somehting on the inveter operation?

 

[ggunn]

I may have a little bit of a misunderstanding of Rapid shutdown. I was under the impression that rapid shutdown is a "stop generating" command via the RSD. Does this RSD also disconnect the ungrounded conductors? It seems like the RSD alone would not satisfy 2023 690.13(E). Maybe I am missing somehting on the inveter operation?

The Sunspec protocol is a common implementation of rapid shutdown in systems with string inverters. In this scheme the inverter generates an AC "keep alive" signal that is superimposed on the DC conductors, and RSD components like those manufactured by Tigo are connected in series in the DC circuits with one or two modules each. When the inverter shuts off as it would when the grid goes down, the "keep alive" signal is no longer present on the DC lines, so in response the rapid shutdown devices disconnect the PV modules from the inverter and from each other. Since nearly all PV systems these days are only functionally grounded on the DC side, I surmise that both the positive and negative conductors from the modules are disconnected, but I do not know that for sure.

 

[pv_n00b]

The confusion might be that RSD, 690.12, does not provide the PV system disconnect required by 690.13(E). These are two distinct requirements in the NEC. The PV system disconnect is often used as the RSD initiation device, but only because opening it will result in a grid tied inverter shutting down and that shutdown typically initiates the DC RSD system.

 

[jaggedben]

I may have a little bit of a misunderstanding of Rapid shutdown. I was under the impression that rapid shutdown is a "stop generating" command via the RSD. Does this RSD also disconnect the ungrounded conductors?

Rapid Shutdown is different than 'stop generating'. It has to do with voltage present in the solar arrays, which may still be an issue when the system output is disconnected. The code lays out the specific requirements in 690.12.

Systems may be engineered so that the 690.13(E) disconnect is also Rapid Shutdown initiation device, but this can't be assumed and isn't code required.

It seems like the RSD alone would not satisfy 2023 690.13(E).

Correct. And vice versa.

Maybe I am missing somehting on the inveter operation?

You can't generalize how rapid shutdown works to all types of inverters. String inverters, microinverters, and inverters that require optimizers all comply with rapid shutdown in very different ways. Some of the details of how it's implemented are trade secrets and we rely on the compliance certifications or field verification of the results to know that it works.

 

[ggunn]

You can't generalize how rapid shutdown works to all types of inverters. String inverters, microinverters, and inverters that require optimizers all comply with rapid shutdown in very different ways. Some of the details of how it's implemented are trade secrets and we rely on the compliance certifications or field verification of the results to know that it works.

I will just add that if the method you are using is to build a system with Sunspec equipped inverters and RSD boxes in the array, it is imperative that you verify that the specific inverters and RSD boxes you choose are compatible with each other. Not all combinations work.

 

[pv_n00b]

I'll also add that if possible try to use one of the UL 3741 listed PV arrays. Then RSD inside the array is not an issue, PV hazard control is built in.