690.12 Rapid Shutdown Exception No.3 PI

[tortuga]

Greetings group I am kicking around an idea for a exception #3 to 690.12 for small 'corner case' PV systems:

Exception No.3 Where a PV system does not exceed 144 Square Feet in area, 2000 Watts DC and 250 Volts Open Circuit Voltage in any string rapid shutdown shall not be required.
This exception shall be limited to one PV system per building.


By limiting the maximum area to 12X12 and voltage to 250V such systems would be a very low risk to emergency responders.
This would carve out an exception for:
Smaller PV systems.
A PV system that is part on a carport and part on a roof.
Older PV systems that get updated or relocated (or like re-roofing).
Older systems that stay in place when new systems are installed.

Any input on how to best word it?

 

[shockdudude]

I would keep it to yourself ,Bad idea..... at low risk. on a sunny day, sounds like cheap easy unsafe greed...

 

[tortuga]

I would keep it to yourself ,Bad idea..... at low risk. on a sunny day, sounds like cheap easy unsafe greed...

Thanks for the feedback, its not about that.
Small PV systems are not the types of systems that have caused problems for firefighters. An exception should be added to allow these systems to be serviced or installed without rapid shutdown.
In developing the UL3741 standard (product category QIJR), Sandia National labs along with UL conducted extensive analyses of all aspects of firefighter operations, including what types of personal protective equipment (PPE) the firefighters wear, the fire-retardant chemicals that they use, and how they put out fires. The UL3741 standard allows firefighters to come into contact well over 80 Volts.
After reviewing this new literature I feel like an exception could be added.

 

[tortuga]

After some off forum input (thank you all for that) here is my next draft:

Exception No.3 Rapid shutdown shall not be required where a PV system has a disconnecting means for isolating photovoltaic equipment meeting 690.15(A)(1) installed at the array boundary, does not exceed 20% of the roof area and does not exceed any of the following:
(a) 144 Square Feet in area.
(b) 2000 Watts DC.
(c) 300 Volts Open Circuit Voltage.
This exception shall be limited to one PV system per building.

 

[don_resqcapt19]

I am sure that 144 square foot area would be exactly where I need to cut my ventilation hole based on the interior fire location and conditions.

 

[tortuga]

I am sure that 144 square foot area would be exactly where I need to cut my ventilation hole based on the interior fire location and conditions.

That is good feedback thank you.
how big of a roof do you think a 144 SQFT area would not matter?
I was basing that on a 12X12 footprint of a 720 SQFT roof and other common rooftop obstructions found on roofs.

 

[don_resqcapt19]

That is good feedback thank you.
how big of a roof do you think a 144 SQFT area would not matter?
I was basing that on a 12X12 footprint of a 720 SQFT roof and other common rooftop obstructions found on roofs.

Every fire is different, and ideally you vent directly over the fire. It could be worked around, but just a concern.

 

[jaggedben]

I am sure that 144 square foot area would be exactly where I need to cut my ventilation hole based on the interior fire location and conditions.

What does that have to do with requiring rapid shutdown? Are you going to cut through the modules?

 

[don_resqcapt19]

What does that have to do with requiring rapid shutdown? Are you going to cut through the modules

Would not cut through the modules, but there may be power where we want to cut if they are not shut down.

 

[letgomywago]

What would it take then to make a system small enough and quick enough to disconnect that this wouldn't be a concern? The connectors they use are touch safe so if it could be quickly removed without danger then what would be the issue if the size install this would exclude? Even if new hardware was needed for making it quickly removable that could be added now if included in this requirement. Something requiring non tamper screws and bolts would make it quick enough for a fireman to remove the panel and cut the attic hole. They cut into tile roofs so having a couple bolts and screws wouldn't add much more time. Even with rapid shutdown it will pose this problem anyway.

 

[jaggedben]

Would not cut through the modules, but there may be power where we want to cut if they are not shut down.

There used to be another section that dealt with that but I guess they got rid of it now they assune everything has RSD.

 

[jaggedben]

What would it take then to make a system small enough and quick enough to disconnect that this wouldn't be a concern? The connectors they use are touch safe so if it could be quickly removed without danger then what would be the issue if the size install this would exclude? Even if new hardware was needed for making it quickly removable that could be added now if included in this requirement. Something requiring non tamper screws and bolts would make it quick enough for a fireman to remove the panel and cut the attic hole. They cut into tile roofs so having a couple bolts and screws wouldn't add much more time. Even with rapid shutdown it will pose this problem anyway.

I don't see what removal has to do with any of this. Rapid Shutdown is principally about assuring firefighters that it's safe enough to conduct operations on the building at all.

 

[letgomywago]

I don't see what removal has to do with any of this. Rapid Shutdown is principally about assuring firefighters that it's safe enough to conduct operations on the building at all.

The PI is about this but the separate issue of a fireman being able to cut a hole in an attic was brought up.

 

[jaggedben]

Right, that was brought up because cutting a hole might expose the firefighter to high DC voltage even if the utility service is turned off. Not because the panels prevent cutting a hole, there are other (non-NEC) rules for that.
I don't really get how tortuga will justify that his thresholds make sense safety wise.

 

[letgomywago]

Right, that was brought up because cutting a hole might expose the firefighter to high DC voltage even if the utility service is turned off. Not because the panels prevent cutting a hole, there are other (non-NEC) rules for that.
I don't really get how tortuga will justify that his thresholds make sense safety wise.

I think this might have been an easier sell before the rules were all accepted by the manufacturers. That said bringing other standards into agreement on what's safe and what's not then that's understandable. If a firefighter needs to assume that the panels are live to their level of ppe and training then I can see that so long as the math works out that they're not exposed to more then it's safe.

 

[tortuga]

I think this might have been an easier sell before the rules were all accepted by the manufacturers.

The studies by Sandia national labs (used to create UL 3741) pretty much showed that firefighters in used/worn ppe gear are at almost no risk encountering up to 600 VDC, I almost used 600V in the proposal.

Right, that was brought up because cutting a hole might expose the firefighter to high DC voltage even if the utility service is turned off. Not because the panels prevent cutting a hole, there are other (non-NEC) rules for that.
I don't really get how tortuga will justify that his thresholds make sense safety wise.

The proposal requires a disconnect [ the reference to 690.15(A)(1) ] much like an HVAC disconnect at the array boundary. 690.15(C)(3) covers the details.
So if Don (thank you Don for saving me) goes up on my roof to fight a fire, per my exception my roof is not going to be smaller than 720 SQFT, the array would be 1/5 of the roof 144 SQFT max, at the array boundary there would be a disconnect similar to an HVAC system disconnect that would de-energize the conductors.
Also I could have a UL3741 system on my roof that leaves Don exposed to a similar voltage even after the rapid shutdown is engaged.

 

[letgomywago]

The studies by Sandia national labs (used to create UL 3741) pretty much showed that firefighters in used/worn ppe gear are at almost no risk encountering up to 600 VDC, I almost used 600V in the proposal.

The proposal requires a disconnect [ the reference to 690.15(A)(1) ] much like an HVAC disconnect at the array boundary. 690.15(C)(3) covers the details.
So if Don (thank you Don for saving me) goes up on my roof to fight a fire, per my exception my roof is not going to be smaller than 720 SQFT, the array would be 1/5 of the roof 144 SQFT max, at the array boundary there would be a disconnect similar to an HVAC system disconnect that would de-energize the conductors.
Also I could have a UL3741 system on my roof that leaves Don exposed to a similar voltage even after the rapid shutdown is engaged.

Maybe it'd be good to include the total percentage to say that at most 20% of roof coverage. As silly as it is I've seen some crazy small houses and can understand the concern.

 

[jaggedben]

I honestly don't see what the percentage coverage has to do with any safety issue related to rapid shutdown. If it's that small of a building what's the issue?

 

[letgomywago]

I honestly don't see what the percentage coverage has to do with any safety issue related to rapid shutdown. If it's that small of a building what's the issue?

That's a good point

 

[don_resqcapt19]

The studies by Sandia national labs (used to create UL 3741) pretty much showed that firefighters in used/worn ppe gear are at almost no risk encountering up to 600 VDC, I almost used 600V in the proposal.

The proposal requires a disconnect [ the reference to 690.15(A)(1) ] much like an HVAC disconnect at the array boundary. 690.15(C)(3) covers the details.
So if Don (thank you Don for saving me) goes up on my roof to fight a fire, per my exception my roof is not going to be smaller than 720 SQFT, the array would be 1/5 of the roof 144 SQFT max, at the array boundary there would be a disconnect similar to an HVAC system disconnect that would de-energize the conductors.
Also I could have a UL3741 system on my roof that leaves Don exposed to a similar voltage even after the rapid shutdown is engaged.

Can't imagine my soaking wet firefighter gloves provides any voltage protection in the real world.

If your panels are in my way, might just fire up the 2000 GPM straight tip on the tower and wash them off the roof