Ever since the 2017 National Electrical Code (NEC) was published, rooftop solar contractors have faced potentially time-intensive and costly safety requirements for module-level rapid shutdown. The code requires installers to utilize module-level power electronics capable of lowering each module’s voltage to 80 V or less within 30 seconds of rapid shutdown initiation to protect first responders. On smaller residential systems, rapid shutdown devices might add only a few extra minutes of install time and minor additional cost. But on huge commercial rooftops, they create a much larger challenge.
The 2017 code did include other ways besides using MLPE to satisfy this safety requirement, but they weren’t as easily attainable.
“Everybody is doing MLPE because that, up to recently, was the only way to meet the requirement, and right now it’s probably still the easiest way to meet the requirement primarily just because of equipment availability, AHJ acceptance [and] firefighter acceptance,” said Ryan Mayfield, founder of solar design firm Mayfield Renewables.
That won’t be the case for much longer. With manufacturing and testing finally in place, installers have a new option to satisfy fire safety requirements on solar rooftops — PV Hazard Control systems.
This option, listed as UL 3741, has been included in the code since 2020, but only now are products getting tested and certified to the standard.
To achieve UL 3741 certification, products must pass a series of tests designed to simulate situations firefighters may encounter on a solar rooftop. The testing analyzes what happens when first responders fall on damaged solar panels while wearing typical protective gear. There’s no prescribed combination of solar products to satisfy this new rating; the merits of each submitted product or product combination are scrutinized during testing.
The goal of the new standard is to make rooftop arrays safer for firefighters in an emergency. Some in the industry say 3741 certification is much more rigorous and scientific than rapid shutdown certification.
“I don’t know if I’ll get anybody ever on record from the code-making panels, but I have heard over and over again that 80 V was semi- pulled out of the air,” Mayfield said. “ is based on a collective science and a collective agreement from the firefighter community, the electrical community.”
So far, at least one system by SMA and Sollega and one by SolarEdge have passed UL 3741 testing. The SMA collaboration uses the company’s Sunny Tripower CORE1 inverters paired with Sollega’s FastRack 510 mounting system — made of polymer material.
“[SMA] thought we were a good candidate given that our racking is polymer and non-conductive, and we worked together to achieve it,” said Elie Rothschild, sales manager at racking manufacturer Sollega. “What we’ve shown through the UL 3741 certification is that there’s a high degree of safety to prevent the firefighters from interacting with the array in any way that would cause them to become part of the current path and thus be subject to a shock hazard.”
In the SMA + Sollega system, wires are routed underneath both the modules and the non-conductive racking, which UL believed to be adequate to guard firefighters from a potential shock hazard when designed to specific requirements — including using nylon zip ties with a necessary air gap to ensure wires do not come in contact with the aluminum module frames.
“This is going to require that we are installing it to a specific way and we’re …….