Introduction

National Electrical Code (NEC) requirements for rooftop solar have evolved steadily since the 2014 introduction of rapid shutdown. These provisions were designed to protect first responders from electrical hazards when working near photovoltaic arrays. Until recently, the most common compliance method involved module-level power electronics (MLPEs) on every panel to reduce voltage during emergencies.

With the publication of UL 3741, the Photovoltaic Hazard Control Code, developers now have additional pathways. UL 3741 defines system-level approaches that control hazards without requiring MLPEs across the array. Plankton Energy recently applied this approach in a 641-kilowatt rooftop solar system for ShopRite of Elmsford, demonstrating how UL 3741 can reshape system design.

What UL 3741 Is

Listing equipment to the UL 3741 standard is recognized under NEC Section 690.12 as one way to meet rapid shutdown requirements within an array boundary. A system listed to UL 3741 could be a combination of a specific string inverter, specific racking, and specific wire management system all tested as a system to ensure the system demonstrates good hazard control. Alternative methods of meeting rapid shutdown requirements, such as installing MLPE devices  to control the output of PV panels at the panel level, are still accepted under the NEC and widely used. This is a key design difference: a UL 3741 listed system allows string inverters to be distributed within the array boundary rather than requiring MLPEs at each module. Regardless of the method employed within the array boundary, upon rapid shutdown initiation all conductors outside the array boundary must be limited to ≤30 V within 30 seconds

It is important to note that UL 3741 is not mandatory and does not imply that systems built without it are unsafe. MLPE-based systems and other NEC-approved methods remain fully compliant and reliable. UL 3741 simply broadens the compliance toolkit available to engineers and installers.

Why UL 3741 Matters for System Design

For developers and EPCs, UL 3741 introduces several advantages:

• Parallel Compliance Pathways –  Expand the system design options available to meet NEC rapid shutdown compliance. Within the NEC 2020 code and onwards, rapid shutdown within an array can now be achieved through MLPEs, a UL 3741 listed system combination of inverters and racking, certified inverters, or UL 3741-certified racking and wire management.
  
  
• Reduced Hardware – Many UL 3741 systems minimize or eliminate the need for module-level shutdown devices, simplifying installation.
  
  
• Operational Simplicity – Fewer components mean less potential for failures and lower maintenance complexity.
  
  

These benefits depend on the specific equipment combination chosen, and cost and operational impacts can vary. 

Case Study: ShopRite of Elmsford

Plankton Energy energized a 641-kilowatt rooftop solar system for ShopRite of Elmsford in New York. The array uses more than 1,280 modules and is expected to generate over 775,300 kilowatt-hours annually. Over its lifetime, the system will save the store more than $1.8 million in electricity costs while avoiding more than 6,100 metric tons of carbon emissions.

The project was supported by New York’s NY-Sun Megawatt Block Program, which provides financial incentives to accelerate clean energy deployment.

UL 3741 Integration

This project is among the first in the region to utilize UL 3741 compliance. Instead of relying solely on module-level shutdown devices, Plankton designed the array with inverters placed throughout the rooftop. This approach:

• Enabled compliance with NEC 690.12 using the UL 3741 standard.
  
  
• Reduced dependence on MLPEs while maintaining firefighter safety.
  
  
• Streamlined array wiring and reduced points of failure.

The ShopRite installation demonstrates how UL 3741 can be applied at scale for large retail rooftops, offering developers more options when approaching NEC rapid shutdown requirements.

Conclusion

UL 3741 does not replace other NEC-approved methods or render them obsolete. Systems designed with MLPEs remain fully safe and compliant. What UL 3741 does is expand the paths to compliance available to designers, installers, and developers.

By allowing inverter placement within the array and defining system-level hazard controls, UL 3741 enables projects like ShopRite of Elmsford to achieve compliance while optimizing system design. For developers, it represents an opportunity to align engineering practices with evolving codes while maintaining safety, reliability, and performance.

Plankton Energy structures each project ensuring  code compliance, system performance, and long-term value. The ShopRite of Elmsford rooftop solar project illustrates how UL 3741 can be implemented effectively.

Contact Plankton Energy to learn more about UL 3741 design pathways and how they may benefit upcoming projects.