New Code Requirements

[inetdog]

I have not talked to others yet about exactly how to implement it, but it is not isolating a string, it is isolating every individual panel from what I can ascertain.

That depends on how you interpret the slightly contradictory parts of the new code section.
The first part describes a maximum voltage conductor to conductor or conductor to ground applying to each individual module output.
The second part categorically exempts all wires which do not extend more than 10 feet from the array or more than 5 feet into the building, whichever is smaller.

The common interpretation (as far as any AHJs have said anything at all ) is that the second section exempts or limits the application of the more strictly worded provisions of the first section.
You will see that point of view represented clearly over at Mike Holt.
But that is no guarantee that some AHJ will not have a different interpretation.

My personal analysis (without access to the guy who actually wrote the new text) is that in a later code cycle the exception will be removed, leaving the stricter first part in effect without having to change the wording of that part.

I agree that if the overriding concern is firefighter safety, sparing no expense, you should put in module level disconnects or module level shorting relays whether the code requires it or not.

The application to commercial/industrial scale arrays on roofs will be truly entertaining.

[Sunking]

Update here is the actual language that made it in NEC 2014.

690.12 Rapid Shutdown of PV Systems on Buildings PV system circuits installed on or in buildings shall include a rapid shutdown function that controls specific conductors in accordance with 690.12(1) through (5) as follows.

(1) Requirements for controlled conductors shall apply only to PV system conductors of more than 1.5 m (5 ft) in length inside a building, or more than 3 m (10 ft) from a PV array.
(2) Controlled conductors shall be limited to not more than 30 volts and 240 volt-amperes within 10 seconds of rapid shutdown initiation.
(3) Voltage and power shall be measured between any two conductors and between any conductor and ground.
(4) The rapid shutdown initiation methods shall be labeled in accordance with 690.56(B).
(5) Equipment that performs the rapid shutdown shall be listed and identified.

It is causing quite a stir in professional forums. The way I see this is it is going to make companies like Enphase very happy because what this implies is a Module Level Shutdown. String Inverter manufactures will be antiquated or have to start making module inverters. If I owned stock in something like Sunnyboy I would be selling it yesterday.

[thastinger]

This is pretty interesting. When I did my off-grid install a little over a year ago it was, and still is, the only one in the county or at least the only one to ever pull a permit to do it. The volunteer fire chief came over to take a look at it with the building inspector. I did all the reflective interior labels for the disconnect source, metal conduit from the disconnect to the roof penetration etc. It would likely burn to the ground anyways before the volunteer firesquad would get there and there are no hydrants around so the 400ish gallons on the truck is all there would be to fight a fire with. I've got the arc fault sensitivity on the classic 200 set as sensitive as it'll go but I actually wouldn't mind doing this panel disconnect via some sort of elctro-mechanical switch before it enters the building. So, how could I do this for my single 5 in series string?

[SunEagle]

Update here is the actual language that made it in NEC 2014.
[SIZE=4]
[COLOR=#000000][I][B]690.12 Rapid Shutdown of PV Systems on Buildings PV system circuits installed on or in buildings shall include a rapid shutdown function that controls specific conductors in accordance with 690.12(1) through (5) as follows.


(2) Controlled conductors shall be limited to not more than 30 volts and 240 volt-amperes within 10 seconds of rapid shutdown initiation.

Maybe I am reading item on line (2) incorrectly but I think it states that it is limiting the panel wiring to 30 volts and 240 volt-amperes. Most grid tie panels are more than 30 Voc and anything over 250 watts would not be allowed.

I hope I am incorrect in my assumption.

[Naptown]

If I am reading this correctly the only controlled conductors are those that are more than 10' from an array or longer than 5' within a building.
With that in mind you could set a disconnect contactor at the combiner or within 10' of an array that would effectively shut down the conductors outside the array but still leave open circuit voltages at the array itself and this would be legal.

[Sunking]

If I am reading this correctly the only controlled conductors are those that are more than 10' from an array or longer than 5' within a building.
With that in mind you could set a disconnect contactor at the combiner or within 10' of an array that would effectively shut down the conductors outside the array but still leave open circuit voltages at the array itself and this would be legal.

Yes Rich I think that is a reasonable interpretation.

Now with that said the code relaxed the wording a bit until the 2017 code cycle to give manufacture ample time to develop micro-inverters that can offer module level isolation. In 2017 it will be changed so the only way to do this is at the module level. None the less as worded now will add significant cost to an installation.

[Ian S]

Maybe I am reading item on line (2) incorrectly but I think it states that it is limiting the panel wiring to 30 volts and 240 volt-amperes. Most grid tie panels are more than 30 Voc and anything over 250 watts would not be allowed.

I hope I am incorrect in my assumption.

The way I read it is that after rapid shutdown is initiated, the system has 10 seconds to reduce voltage and wattage to the required levels in any conductor further than 10 feet from the array or inside the building. It would seem to me that it could be either done at the panel level or perhaps even at the point where the main conductors leave an array. Whichever way it is done,will at the least add more complexity and more points of potential failure I suppose.

[Naptown]

Yes Rich I think that is a reasonable interpretation.

Now with that said the code relaxed the wording a bit until the 2017 code cycle to give manufacture ample time to develop micro-inverters that can offer module level isolation. In 2017 it will be changed so the only way to do this is at the module level. None the less as worded now will add significant cost to an installation.

This could also be accomplished I would think with a solid state contactor(s) to short the strings at the inverter, dropping array voltage to 0.
Since the array would be shorted there would be no VA measurement as the voltage would be 0.

If this is to protect firefighters it will do nothing as the array will be energized even with a disconnect at the array.

[Naptown]

Yes Rich I think that is a reasonable interpretation.

Now with that said the code relaxed the wording a bit until the 2017 code cycle to give manufacture ample time to develop micro-inverters that can offer module level isolation. In 2017 it will be changed so the only way to do this is at the module level. None the less as worded now will add significant cost to an installation.

You still have the issue of modules with an open circuit voltage of more than 30V. So good bye any module greater than about 50 cells

[OvertheSun]

This could also be accomplished I would think with a solid state contactor(s) to short the strings at the inverter, dropping array voltage to 0.
Since the array would be shorted there would be no VA measurement as the voltage would be 0.

If this is to protect firefighters it will do nothing as the array will be energized even with a disconnect at the array.

So, overall, would a better solution be a safety device that blocks light getting to the panel? A low-tech device, like some sort of retractable cover?

[bcroe]

Emergency Covering Panels

So, overall, would a better solution be a safety device that blocks light
getting to the panel? A low-tech device, like some sort of retractable cover?

That will never fly. My panels are currently in the grip of below zero ice (but working),
trying to mechanically cover the panels would never work here. Even if covered, light
on the back side would be enough to be dangerous. Bruce Roe

[inetdog]

The way I read it is that after rapid shutdown is initiated, the system has 10 seconds to reduce voltage and wattage to the required levels in any conductor further than 10 feet from the array or inside the building. It would seem to me that it could be either done at the panel level or perhaps even at the point where the main conductors leave an array. Whichever way it is done,will at the least add more complexity and more points of potential failure I suppose.

A correct interpretation. The idea behind the 10 second window is that some inverters or charge controllers might contain capacitors for input energy storage or storage at the DC to DC convertor level inside or output energy filtering. Even when you remove the DC applied to the input, it could take some time to safely discharge those capacitors.
Now I am not aware of any equipment that really does have that level of energy storage, but I am open to examples.

[OvertheSun]

That will never fly. My panels are currently in the grip of below zero ice (but working),
trying to mechanically cover the panels would never work here. Even if covered, light
on the back side would be enough to be dangerous. Bruce Roe

Hearing about all the snow and bitter cold makes me glad I moved out here from Chicago area. Don't miss the snow one bit.

Maybe you could invent a solar panel add-on device that has multiple functions. Mini snow plow leading edge & retractable cover! Could cover both sides. Maybe put some water jets in there to wash the panels off (when its not freezing, of course) -- even a soft, non-scratching brush. Flame retardant material.... Non-slip, non-conductive surface to keep the fire fighters safe? The possibilities are endless.

[J.P.M.]

Hearing about all the snow and bitter cold makes me glad I moved out here from Chicago area. Don't miss the snow one bit.

Maybe you could invent a solar panel add-on device that has multiple functions. Mini snow plow leading edge & retractable cover! Could cover both sides. Maybe put some water jets in there to wash the panels off (when its not freezing, of course) -- even a soft, non-scratching brush. Flame retardant material.... Non-slip, non-conductive surface to keep the fire fighters safe? The possibilities are endless.

How about heated glass like window defrosters?

[inetdog]

How about heated glass like window defrosters?

And solar powered, once the snow is off the panels....