Mike Dolt Enterprises
Mike Dolt Enterprises
User: parallel_fuses, Location: US
Asked on: Tuesday, December 3, 2024 at 5:16 pm EST
Answered on: Thursday, March 6, 2025 at 5:52 am EST
Question: In jurisdictions still using the 2017 NEC is UL3741 an acceptable means of hazard control or are module level rapid shutdown devices required?The following article covers the history and evolution of PV hazard control in the NEC, IAEI Magazine: NEC Rapid Shutdown Requirements and UL 3741. After reading the article, particularly the section below, the way I understand it is that although UL3741 did not exist at the time the 2017 NEC was written, provisions for a future means of hazard control were included in the text and UL3741 is an acceptable method.What is your interpretation of the 2017 NEC and UL3741, and especially helpful would be any insight on the interpretations you have encountered of AHJs who still use the 2017 NEC? Thank you!“Of particular relevance to this discussion is Section 690.12(B)(2)(1) of the 2017 NEC, which states, “The PV array shall be listed or field labeled as a rapid shutdown PV array. Such a PV array shall be installed and used in accordance with the instructions included with the rapid shutdown PV array listing or field labeling,”This provided a way for PV contractors and installers to comply with the NEC rapid shutdown requirements without having to install MLPEs. To comply with this new “listed array” requirement, PV equipment manufacturers began to have their products evaluated by nationally recognized testing laboratories (NRTLs) for compatibility with PV equipment from other manufacturers. Not many such arrays have been listed to the standard, mostly because the standard was not published by Underwriter’s Laboratories (UL) until December 2020.In the 2020 NEC, Section 690.12(B)(2)(1) was changed to include a new phrase, “PV hazard control system.” Section 690.12(B)(2)(1) of the 2020 NEC states,“A PV hazard control system listed for the purpose shall be installed in accordance with the instructions included with the listing or field labeling. Where a hazard control system requires initiation to transition to a controlled state, the rapid shutdown initiation device required in 690.12(C) shall perform this initiation.”The Exception to 2020 NEC 690.12(B)(2)(1) refers to UL3741, Standard for Photovoltaic Hazard Control.”
You've correctly interpreted the evolution of the NEC and the place UL 3741 occupies within it. Here's a breakdown of my understanding and likely AHJ interpretations in 2017 NEC jurisdictions
Interpretation of 2017 NEC and UL 3741:
2017 NEC Provisions
The 2017 NEC in 690.12(B)(2)(1) did create a pathway for rapid shutdown compliance other than MLPEs by allowing for "listed or field labeled" rapid shutdown PV arrays. This was forward-thinking and anticipated the development of standards like UL 3741. The key phrase is: "...installed and used in accordance with the instructions included with the rapid shutdown PV array listing or field labeling."
UL 3741 as Compliance
While UL 3741 was not published until after the 2017 NEC was released, once UL 3741 products became available, they could be used to satisfy the rapid shutdown requirements IF the entire system (array) was listed or field labeled and installed according to the listing instructions.
Challenges and Considerations
Listing Limitations
The challenge under the 2017 NEC was getting a complete PV array (modules, inverters, etc.) listed or field labeled as a rapid shutdown PV array. This typically involves a manufacturer submitting their modules/inverters in conjunction with other manufacturers equipment.
AHJ Acceptance
Ultimately, the AHJ has the final say. They will want to see clear documentation that the entire array is listed or field labeled for rapid shutdown to UL 3741, and that the system is installed per the manufacturer's instructions included with that listing.
Manufacturer Responsibility
It is up to the equipment manufacturers to test their products in conjunction with other manufacturer's products, to achieve the UL listing.
Complexity
Implementing a complete UL 3741-listed system can be complex as it requires compatibility between modules and inverters. MLPEs may be an easier alternative.
Likely AHJ Interpretations in 2017 NEC Jurisdictions
Permissive (But Scrutinizing)
An AHJ may allow UL 3741-compliant systems if the installer can provide rock-solid documentation proving the entire system meets the listing requirements and is installed per those instructions. They will look for: Listing documents clearly identifying the modules, inverters, and other components included in the listed array. Installation manuals that explicitly state the system meets UL 3741 and how to install it to maintain that listing. Field labeling verification (if applicable).
Restrictive (Defaulting to MLPEs)
Given the complexity, some AHJs might be hesitant to accept UL 3741 compliance in the 2017 NEC. They may require MLPEs because they are more straightforward to verify.
Recommendations
Early Communication
Contact the AHJ before designing or installing a UL 3741 system in a 2017 NEC jurisdiction. Get their input and approval in writing.2.
Documentation is Key
If the AHJ is open to it, prepare comprehensive documentation showing the complete system is UL 3741-compliant, and that you fully understand and will follow the installation instructions.3.
Consider MLPEs
Be prepared to install MLPEs if the AHJ rejects the UL 3741 approach, or if you encounter insurmountable listing or installation challenges.
In Conclusion:
While the 2017 NEC technically allows* for UL 3741 compliance through the "listed array" provision, its practical application can be difficult due to listing limitations and the AHJ's interpretation. Communication with the AHJ and robust documentation are essential. MLPEs might be the easier and more readily accepted path in many cases. Flag for review