PV LOTO

[bure961]

In a emergency situation when the pv on the roof must be shut down is disconnecting the ac from the inverters enough to put the roof top pv in a safe condition ? Are they put out of service as far as being energized with power coming down to the inverter ? I just don't know anything about pv system to be sure.

 

[ggunn]

In a emergency situation when the pv on the roof must be shut down is disconnecting the ac from the inverters enough to put the roof top pv in a safe condition ? Are they put out of service as far as being energized with power coming down to the inverter ? I just don't know anything about pv system to be sure.

Unfortunately, no. The DC conductors coming down from the roof remain energized unless disconnected from the array. The current stops flowing in the conductors when the inverter is shut down, but the voltage remains and the available fault current is determined by the power rating of the array and the strength of the sunlight striking it (irradiance) at the time. The voltage is pretty much a constant as long as the sun is shining on the array.

 

[don_resqcapt19]

Even artificial light sources, such as lighting used by fire departments for night time firefighting operations, can result in a dangerous open circuit voltage from the PVs.

 

[bure961]

I like to know is it something that can be easily done to make the roof safe for personel to be spraying water or refusing to go to roof because of a fear of electrocution ? How do you insure someone it is safe to do work up there in emergency event. ? We will have to get our pv contractor involved to do this . With knowing what has to be done to accomplish this will be helpful. We have close to 40 panels on roof at this time. Thank you for anymore information you can give.

 

[c_picard]

Massachusetts is now on the 2014 NEC, and rapid shutdown provisions are being enforced. How old is the PV system you are concerned with?

 

[bure961]

Not living in MA. anymore but the PV is atleast 7-8 years old.

 

[jaggedben]

Is the main concern that the fire department would refuse to fight a fire on the building?

If so, I think the solutions would be...

1) Install a DC disconnect close to the array.
2) Educate the fire department on procedures to deal with PV systems. If they don't have training and procedures in place then it doesn't really matter what you do physically to the system.

 

[CodeQuandary]

Micros or string?

Micros or string?

If the system is a microinverter system, then the answer to the orginal question is yes: shutting off the AC will activate the UL1741 anti-islanding circuitry in the inverters, and they will shut down on an individual basis. The nominal voltage from each module to it's corresponding inverter is relatively inconsequential. This may also be true for systems with panel-level optimizers installed, though I'm unsure.

 

[don_resqcapt19]

Is the main concern that the fire department would refuse to fight a fire on the building?

If so, I think the solutions would be...

1) Install a DC disconnect close to the array.
2) Educate the fire department on procedures to deal with PV systems. If they don't have training and procedures in place then it doesn't really matter what you do physically to the system.

It is a lot more than just the DC voltage that concerns the fire departments. It often prevents cutting ventilation holes in the roof where they are needed, and there are concerns for the structural strength of the roof. Some PV systems are installed without anyone checking the structural strength of the roof.

My solution would to be to just fire up the 2,000 GPM (about 8.3 tons of water per minute) straight tip ladder pipe and just blow the panels off the roof and out of my way . In reality the most common solution for a structure fire where there are solar panels, is that the FD just goes into defensive fire firefighting mode.

 

[ggunn]

...Some PV systems are installed without anyone checking the structural strength of the roof.

Seriously? Commercial systems? You know this for a documented fact?

 

[don_resqcapt19]

Seriously? Commercial systems? You know this for a documented fact?

Not much on the commercial side, but there are areas with little of no permitting or inspection for any type of work.

 

[jaggedben]

It is a lot more than just the DC voltage that concerns the fire departments. It often prevents cutting ventilation holes in the roof where they are needed, and there are concerns for the structural strength of the roof. Some PV systems are installed without anyone checking the structural strength of the roof.

...

None of that really concerns the NEC or seems to be relevant to the original subject of this thread.

I will just add that California has pretty good guidelines on fire setbacks and at this point all of the jurisdictions that I work in are enforcing some version of them.