Changes NEC 690.12, Solar Photovoltaic Systems

I didn't bother to read any of that, because it required me to register. Perhaps you could quote whatever matters.

Thank you. How about "Knox Box" technology for this, or similar?

The "Knox Box" system, where a key storage box is remotely controlled, certainly will help in one aspect of the system. A key could be stored there, access remotely given and the key used to lock all necessary enclosures that control the system. The biggest problem then would be how is the power generated by individual panels or groups of panels brought to zero so work activities can be started in that area. Knox Box is part of the solution, a very good one for that segment, but what about the other problem functions and areas?

Last week I attended another briefing on fire fighting where there is solar panels, given by the state's largest power supplier. Their message was that until more improvements are made and proven safe, if there is any doubt- stay off, stay out, stay away and keep water off the panels. Their premises for those are these items can kill you without you knowing it is going happening.

Thanks for the good idea. I will be certain it incorporated in our pending GOG for PV Solar Panels.

Good Luck, Old Salt

Thanks. It is a very good point you shared with us.

Thank you all for your obviously very intelligent and well thought out answers.

As some of you have stated, this is a subject that must be resolved by all those involved with the situation. It isn't just the fire fighters well being that must be considered but also the maintenance personnel, the owners, the manufacturers, the installers, inspection personnel and several others.

Ironically, yesterday I saw an old friend who had been a volunteer firefighter and a finishing carpenter. He is now an installer of solar systems. He is no longer involved with fire activities but his concern for the systems and the problems they are confronted with in maneuvering around them during installation and maintenance has become forefront in his mind. He had no all inclusive answer but has great concern about his health and safety while working up on a crowded roof.

Not until every function involved realizes that they need the support of all others, including compromises, to bring together a safer system and procedures will this become a "safe" subject. It has been done in other industries, the time is now for PV solar panels.

Good Luck, Old Salt

Mr. Old salt,

Since the PV power output is directly proportional to the amount of light it receives, cutting off the light source or limiting its exposure to sunlight will also cut off the PV's power output to the minimum or safe level.. By having a black or dark colored chemical foaming fire suppressants sprayed on those PV panels may facilitate disabling of those panels, thus improving the safety aspects for the responding firefighters..

Just another thought...

Yes, the objective of the changes are to make it safer for firefighters to work at structures with PV panels. I know of no suppressing foams that are other than white when applied. A dark color would also hide the area that they were working in, such as a roof with panels, making it more dangerous to be there. Also when foams are applied initially they tend to run down the surface thus decreasing their effectiveness in blocking light. This would make it more dangerous for the firefighters. How would it be possible to cover all panels at one time and to maintain that light blocking property to keep the power off initially?

The original article had this picture:

In it firefighters are using tarps with very low light transmittal to cover the panels. The primary problems with this are those in the picture only have about 10-15 lbs of gear on. A full equipped fire fighter has over 70 lbs on plus then the tools (axe, haligan tool, saw, hand light) adds up to over 100lbs. Add to that the weight of the tarps and its a very heavy load especially for a 150 lbs person. Another problem is footing on the roof that is almost completely covered by panels, where do you walk or stand? How long will it take to put the tarps in place and secure them? What is done if the fire is below the panels and a hole needs to be cut in the roof below them for venting purposes?

I don't know the answers to all these questions. That's why I posted this subject. I greatly appreciate your input. Having been involved with these I am aware that much needs to be done about the panels and their systems, for the user, the maintenance personnel, the owners, the manufacturers of the systems, the installers and the fire fighters.

Good Luck, Old Salt

Old salt how about marking the voltages on the system in question, with a cut out switch at ground level in a Knox box controlled switch. Just saying most, not all of the systems that I have seen have all been 12,24, or 48 V DC. Is this a viable solution or not. Duke

The Knox Box is a good idea for the controls. Unfortunately many of the newer installations operate at higher dc voltages. The unabridged article mentioned:

The standard recognizes that DC ranging from 300VDC to 600VDC is typically present in array wiring, combiners, and other exposed system components even after a building's main AC power is shut down. It's that electricity, generated by the solar panels and transformed to usable AC through inverters, that could badly shock firefighters as they walk on or hack through roofing in close proximity to panels and associated wiring and components.

In many systems the panels are connected in series and then these sets connected in parallel to each other. Combine that with the lack of walking space between powered, or potentially powered, panels and the often times wet conditions sets up a potentially fatal incident if someone fell onto a panel. Also water can't be applied to these panels without the danger of a shock, just like putting water onto a live electrical wire.

Still open to many more suggestions. Keep them coming!

Good Luck, Old Salt

Thanks so much for this discussion. A few notes. We are building systems now that are nominal 1000VDC systems. There could be consistant votages at 850VDC common in these systems.

Danger to firefighters from these PV systems is DC only. It could be from module output in serial and or parallel configrations to step a 40V module up, but also from some internal inverter components that can remain energized for up to five minutes after the power supply (either grid or PV ) is disconnected. However, the danger on the roof is all DC, even if the inverters are roof mounted, if ff have killed the grid. I am assuming that ff always kill the grid before they fight a burning structure. Is this correct?

All inverters in the US are UL1740, which means, in the event of a fire, when a ff pulls a grid supply primary meter head or disconnect, all inverters are disabled on the AC output side. By definition, it opens the circuit on the DC conductors supply side, but a short on the PV array could close that circuit, leading to ff danger when working around potentially damaged modules and wiring, as would be the case in a fire. So the proposed solution, the ten foot emergency shutdown rule, may decrease the amount of potentially live circuits, but does not solve the problem. The PV array (and associated grounded array racking) is still a potential short. In this case, the equipment ground actually increases the danger.

Falling onto a module may be hazardous, because it is possible that you could create a good solid path to ground, but I think that is not the primary danger. Hacking through a metallic conduit that has 20 amps at 850V could be tragic.

NEC 2014 705 has good requirements to deal with equipment crowding on the roof. Roof corridor creation is just common sense. It even requires (suggests) f marshall approval in some scenarios, a very good thing. Most ff I have met don't want to be on a roof, period. They want to eradicate the fire from a stable remote platform. If it's an industrial facility that cannot be controlled from these platforms, I have serious reservations about trying to imply that we can , as an industry, make them safe to work around if they have power generating systems that are active. Is it safe to fight a fire that is adjacent to a fuel tank? Maybe we should give ff's more information about the structures they are protecting.

Thanks for the discussion.

On another note, I am aware that NAVFAC and San Diego FD have raised concerns of overcrowding a roof top to maximize PV collection to the point that roof access for HVAC maintenance or fire fighting is impossible.

Solar designers need to be made aware of these issues before the panels are installed, and maintenance and fire fighting personnel need to be aware of the risks around solar panels. The only safe way to kill the power is to cover the PV panels so they do not generate power, but during an emergency this is very limited in practicality.

I do not have a simple recommedation to solve this issue, aside from educating designers, owners, maintenance, and fire fighters of the hazards from solar equipment on rooftops.