UL 3741 PVHCS Placarding

[SteveO NE]

Since we are starting to see more systems become passively capable of meeting UL3741, what are you guys doing with the disconnect placarding (i.e. the Rapid Shutdown, or lack thereof, placarding)? By passive, I mean systems with no MPLE or switches of any kind, they are just able to meet UL3741 with no additional active switching on the DC side of the system all the time. It's funny that the 2023 moved all other definitions to Art 100 and then added new ones (PVHCS, PVRSE, PVHCE), that nobody really understands to Art 690 with no mention in Art 100, no definition at all, and very little guidance other than to read UL3741 for yourself.

Personally, seeing as there seems to be lack of guidance, or I've missed it, I have been labeling stating exactly that. "This building contains a PV System that may remain energized above 80V even upon opening this disconnect switch and is certified by UL 3741 to meet a Hazard Level of X providing all standard Firefighting PPE is worn and properly maintained."

In reality we have been dealing with this for a while with systems like SolarEdge where the optimizers were switched back to series to reduce current with larger modules but it was sneaky, there is still MLPE, it just remains over 80V and is generally speaking a Hazard Level 1 which means they shouldn't expect to experience anything, and even without PPE would probably not have more than a "tingling sensation." As such nobody has even noticed it, in fact I know plenty of engineers that had a bit of an uh-oh moment in retrospect where they had to brush up on UL 3741 after they realized they've been installing those systems that dont strictly meet rapid shutdown requirements. As the Hazard Levels increase though, this seems to be prudent to point out that the system is only at that hazard level when they are wearing full PPE.

Personally, as a side note, what I hope for is that it becomes required as part of their certification that design/installation specifications state the certified hazard level in an easy to find location - for instance a system can still be passive with a Hazard Level 3 for someone spraying water on energized components; however, that hazard level is 100mA which is consider by UL the limit, with a 66% factor of safety to fibrillation, and serious injury. That means that firefighter is going to feel it. The testing doesn't really consider the fire fighters reaction to that unexpected shock, especially in a compromised area like standing in the measly 3/4' setback at the roof's edge.

For instance, the SE P1101's spec sheet says "SAFETY | IEC62109-1 (class II safety), UL1741, UL3741, CSA C22.2#107.1" and you can subsequently look for and find their published document, "UL 3741 Compliance – SolarEdge’s DC Optimization Architecture – Application Note" which tells you that it is a Hazard Level 1. I think that UL should have a suffix that identifies the certified hazard level like "UL3741-HL1"

 

[pv_n00b]

Since the 690.12 RSD system covers controlled conductors inside and outside the array boundary PVHCS will not cover all the controlled conductors. Even with an intrinsically safe PVHCS system in the array there will still be an initiation device to deenergize the conductors outside the array boundary. The placard in 690.12(D) is still required and needs to indicate what initiation device is used, typically either the service disconnect or a stop button, to deenergize the controlled conductors that do not fall undo PVHCS control.

I would not want to be the one to dissuade you from offering additional information over what is required in 690.12(D) but at the same time I would keep in mind that fire fighters are already going to know about the PPE they need to use around a PV array. There is no need to make a distinction between a PV array with a 690.12(B)(2)(1) RSD and a (B)(2)(2) PVHCS as they are intended to provide an equivalent level of safety. The PVHCS array should actually be safer than the RSD array.

 

[SteveO NE]

Yes, I understand that 690.12(A)(2) counts the inverter AC output circuit as part of that, but my issue is that I don't agree with the statement that they are intended to provide an equivalent level of safety - a new (generally speaking) hazard level system has been implemented that identifies various levels of safety. Previously nothing could be energized to over 80V; SolarEdge was quiet and pushed that limit up but stayed within Hazard Level 1. New systems increase that hazard level which is up to and including the firefighters being able to feel a substantial shock when spraying water on the system - it doesn't mean they aren't safe from the shock itself but I certainly wouldn't say you could call it the same level of safety when we have an actual designation that says it's a higher hazard level. Couple that now that the hazard level is identified based upon them wearing properly maintained PPE - that's higher than a level that's safe enough to touch with your bare hands and no EH boots on.

I think the placard in 690.13 (referencing 690.12(D)) is misleading and could lead to person or property damage if the engineer doesn't make it clearly understood what is happening. The moment a firefighter feels a shock and doesn't realize that is normal, and within UL identified safety limits, they will let the building burn. This is the status quo when they don't understand the PV on the roof...they let it burn and blame the PV.

Don't get me wrong, I'm not complaining about a PVHCS system, I think the other side of this discussion is that this requires substantial testing whereas everything before was just assumed to be good enough, but let's face it, this also assumes the fire fighters know what is going on and most of them are just getting the message now about Rapid Shutdown with MLPE.

 

[pv_n00b]

I think you are over simplifying UL 3741. It's a very complex standard and takes into account many factors to determine if PVHC is required. I would refer you to table A.2 in the standard for an example of the full risk assessment.
As stated in section 8.1.1 of the standard

The requirements outlined in this Standard are intended to reduce the likelihood of muscle tetanization (involuntary contraction) and ventricular fibrillation from electrical shock by damaged or undamaged PV arrays during FF operations.

FF are trained in performing their work around electrical equipment in general and PV array in particular.
Water spray conductivity is taken into account in section 10.3 of the standard. This report on FF activities and PV arrays finds:

The electric shock hazard due to application of water is dependent on voltage, water conductivity, distance and spray pattern. A slight adjustment from a solid stream toward a fog pattern (a 10 degree cone angle) reduced measured current below perception level.
A distance of 20 feet had been determined to reduce potential shock hazard from a 1000 Vdc source to a level below 2 mA considered as safe.

https://fsri.org/sites/default/files/2021-07/PV-FF_SafetyFinalReport.pdf

Section 12.2.2 outlines the steps for a analysis of an array under normal conditions. The final result is that hazard levels will be no higher than hazard level zero (12.2.2(e) after initiation of shutdown.
Section 12.2.3 outlines the steps for a analysis of an array under faulted conditions. Under faulted conditions hazard levels above 1 with a frequency of occurrence above 3 are identified as Action required or Action May be Required to lower the hazard level to 1 or 0. It's complicated.
Hazard level 0 is a current range of 0-2.67mA with a "perception with slight pricking sensation. No risk of shock or reaction."
Hazard level 1 is a current range of >2.67-40mA with "Muscle Contraction. Insignificant threat to life or injury. May result in a reaction response."
As you can see it is the current that is evaluated not the voltage. It's a complex path to find the current based on an exposure voltage and the resistance of the person's body and clothing.
As for the RSD option in the NEC. The 80V level was not selected to be safe as that would require an analysis of the induced current in a person in contact with the 80V source. It was the lowest reasonable voltage that could be used to give an allowance for the maximum expected PV module voltage in the future that would ever be used in a PV array that fell under 690.12. If a module voltage exceeded this value then there would need to be internal controls to break up the cell strings and lower the voltage. A requirement that was determined to be financially unworkable.
All this being said I do find that a UL 3741 listed array, with its more exhaustive safety analysis, is more likely safer for FFs to work around than a simple 80V RSD system. Neither system is safe to touch by someone who is not wearing proper PPE. People try to use RSD to make systems "safe" for technicians to work around and this is another myth that is hard to train out of people. That's not the purpose of RSD.