Why does Rapid Shutdown apply to AC Modules

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JoeNorm

Senior Member
Location
WA
I got to thinking today......Why should there be any rapid shutdown requirement for an AC module system? Isn't it just like any other circuit in the house? All of the rules that apply to string inverters are not really applicable to AC modules. The DC conductors are limited to about 8 inches on each module. The rest is regular old AC.

Maybe it doesn't apply and I just haven't been aware of it.

Curious your thoughts on this

Thanks
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Because some PV arrays don't shut down from the AC side, firefighters don't know if your conduit coming off the array is still energized when they shut down the service. So you are still required to put a label on the service stating that the array complies with rapid shutdown, so they can know that it's safe. It just so happens that with AC modules that's all you need to do because the rest of it inherently complies. But you don't get exempted from putting up the signage that says it's safe just because it was safe to begin with.

I'm skeptical that inspectors and firefighters are universally well trained enough on all of this to ensure that firefighters understand and trust the signage. But that's a whole different set of issues.
 

JoeNorm

Senior Member
Location
WA
That makes sense. But maybe AC modules shouldn't be required to have a "rapid shutdown switch," just the stickers that say it is inherent in the system.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
AC modules only need a rapid shutdown switch if the service disconnect doesn't qualify. Say, if the service is inside (2017 NEC) or there's a battery backup that keeps the array energized when the service is shut off.
 

Carultch

Senior Member
Location
Massachusetts
I got to thinking today......Why should there be any rapid shutdown requirement for an AC module system? Isn't it just like any other circuit in the house? All of the rules that apply to string inverters are not really applicable to AC modules. The DC conductors are limited to about 8 inches on each module. The rest is regular old AC.

Maybe it doesn't apply and I just haven't been aware of it.

Curious your thoughts on this

Thanks

The rapid shutdown requirement doesn't cease to exist when you use modules with built-in power electronics that automatically shut down upon loss of grid. It is just that you don't need additional equipment to perform the rapid shutdown, because the microinverters comply by default. You still need to identify that the system is built with rapid shutdown through the labeling, and label it with instructions for how to initiate rapid shutdown. That way it isn't confused with an NEC 2011 system, built prior to this requirement.
 
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