[RE-wrenches] NEC 2014 690.12 Rapid Shutdown

[Daniel Young]

Here is a link for a video where Mike Holt helps with an explanation to your question.

 

https://www.youtube.com/watch?v=sUXShMZJorQ

 

Essentially, the rapid shutdown needs to keep the energized length of conductors to within 10’ of the array if on the roof (this rule is only for arrays on buildings) or within 5’ of building penetration. I would assume that if you are 9’ on the roof, you then only have 1’ in the building before you need the shutdown device.

 

So micro inverters and some DC-DC optimizers should comply with the standard as is (since they prevent wires from being energized with DC voltage before they even leave the array). But string inverter systems will need to get creative with how they address this. Midnite solar disco combiners with the birdhouse seem to be a possible solution, but they add a lot of cost to some smaller systems that didn’t even need combiners before, let alone disconnect combiners with power supply cards and separate control boxes...

 

Hopefully a better solution for small string inverters is on the horizon. 

 

With Regards,

Daniel Young, 

NABCEP Certified PV Installation ProfessionalTM: Cert #031508-90

NABCEP Certified Solar Heating InstallerTM: Cert #SH031409-13

 

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jeffrey Quackenbush
Sent: Tuesday, January 07, 2014 10:46 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] NEC 2014 690.12 Rapid Shutdown

 

I've been going through the new Code book (which is in effect now in Massachusetts) and found myself somewhat puzzled by the intent of the new "rapid shutdown" requirement in 690.12. Does anyone have insight into how this is supposed to be interpreted and implemented? I've put together a list of my own questions, given below (the numbers reference the new 690.12 text). Thanks!

 

690.12 Rapid Shutdown

1.  Where should the rapid shutdown switch be located? (1) only says that the shutdown function should be installed if the circuit is longer than 10’ or goes more than 5’ into a building. If this condition is fulfilled, it says nothing about where the switch should be located. (2) says that controlled conductors should be limited to 30V, 240W, which will only be the case downline from the switch, so this may mean that  it should be located close to the source, i.e. on the roof. But this is just an inference, and one that doesn’t have clear boundaries; every source conductor for a series connected PV circuit (that is not Solar Edge, Enphase , etc.) will have a higher voltage and wattage potential when the sun is shining somewhere along its length, even if the disconnect is located very close to the array. Or does this requirement mean that all systems will need to have some kind of “smart” junction box, module DC-DC converter or module level AC inverter? Furthermore, individual modules often have higher voltages & wattages these days and there is no way to impose limits on their electrical characteristics in any field wired configurations. A listed AC module that sees the module leads as internal would be the only scenario that would be exempt.

 

2. (5) asks that equipment performing the shutdown should be listed and identified. Does that mean listed and identified for the purpose of this specific requirement? Or just listed and identified to limit voltage and wattage in 10 seconds? Does a specific UL standard exist for the function they have in mind? Does any equipment exist that has such listing and identification yet?

 

3. Is the rapid shutdown intended to be automatic or manual? If automatic, what are the parameters that would trigger the shutdown? If manual, are there any accessibility requirements?

 

4. Rapid shutdown seems more like a disconnect requirement than a circuit requirement. Why limit circuits to 30V, 240W, instead of just requiring a shutdown? Why 10 seconds, when all the disconnecting functions (i.e. manual disconnects, and internal AFCI, GFCI & UL 1740 disconnects) happen in less than a second? (It hardly seems like a “rapid” shutdown). Why write this article into section II rather than section III?

 

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