[RE-wrenches] NEC 2014 690.12 Rapid Shutdown

[Mark Frye]

The un-controlled conductor could be up to 15 feet, 10 on the roof and 5 
in the building?

Mark Frye
Berkeley Solar Electric Systems

On 1/15/2014 2:02 PM, Daniel Young wrote:
>
> 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 Professional^TM : Cert #031508-90
>
> NABCEP Certified Solar Heating Installer^TM : 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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