Changing Standards for the PV Industry: UL 61730 for PV Modules and UL 3741 for PV Hazard Control (Rapid Shutdown UL Listing)

Codes and standards are regularly updated for the constantly evolving solar and storage industries. Sean White and Bill Brooks recently updated their advanced codes courses on HeatSpring to include information on UL 61730 and UL 3741. Here’s some information on the new standards. 

UL 61730 – PV Module Safety Standards

UL 61730 is the new PV module UL listing. This new standard is based on the International Electrotechnical Commission (IEC) standard 61730. Note that there is always a 6 in IEC standards. 

The standard actually started in the United States, went to Europe, was adopted there and then came back to the United States. It was based largely on UL 1703 originally, then was modified for the European market. In an attempt to have an international standard that would work everywhere, including the United States, it was essentially brought back and implemented here. Luckily for solar manufacturers, there isn’t a need to double test everything via CE and UL.

If a company launches new products after December 4th, 2019, then they would have to test to the new UL Standard, UL 61730, as opposed to UL 1703. That’s essentially the date where new products have to meet the new requirements. A company could continue to build a product that was built to the UL 1703 standard indefinitely, but they couldn’t make changes.

Bill Brooks is on the UL 1703 Standards Technical Panel, which covers all the standards related directly to PV modules. 

UL 3741 – PV Hazard Control aka Rapid Shutdown Listing

In the NEC, there are 3 ways to comply with the 690.12 Rapid Shutdown requirements within the array. 

1. 690.12(B)(2)(1) is UL 3741 (relatively new and what this article is about)
2. 690.12(B)(2)(1) is 80V after shutdown, which is the way we most often do it and is often referred to as module level shutdown
3. 690.12(B)(2)(3) which requires no metal parts or exposed wiring methods and was developed with Building Integrated PV (BIPV) in mind.

UL 3741 is called PV Hazard Control. It was included in the text of the 2017 NEC, but the UL Standard was not developed until December 8th, 2020. There were never any products listed and available to the public until recently. Now, there is an alternative to module level shutdown, besides the barely used BIPV method.

There are several products already listed and certified to this PV hazard control standard. Tesla was likely the first, however since Tesla products are not available for the public to install, it is probably listed Top Secret and held by the FBI;). They really needed this certification for their power roof product. It is difficult to comply with the BIPV method and the BIPV method is probably not going to be included in the 2023 NEC.

After the NEC 2023 comes out, there will likely be two options: the UL 3741 option, which is very new within the industry – and the 80 volt option says that within 30 seconds of rapid shutdown, the array can have no parts of it that are above 80 volts (in most cases at the module level).

Depending on how the system is put together, there’s a variety of ways of meeting the UL 3741 requirements. If you are using a product that’s UL 3741 listed, then it’s going to include all the information of how it has to go together in order to achieve that listing, including any electronics. Enter mid circuit interrupters or MCIs. Instead of being on every module, mid circuit interrupters might be on every other module, every third module, or every fourth module. It depends on the voltage. 

Major manufacturers of products will likely all go to UL 3741 as a compliance option. There are  financial benefits for these higher voltage compliance options, as opposed to the 80 volt rapid shutdown.

In summary, mid circuit interrupters are going to become commonplace. It’ll be UL 3741 that will define how much voltage you can place on each mid circuit interrupter. If you want to take advantage of higher voltages, then UL 3741 is your friend. Mid circuit interrupters will have their benefits for using primarily string inverters, but it doesn’t mean that they’re going to blow away the DC converter market or the microinverter market, which still together make up 80% of the residential market.

Stay tuned for the next article in this series where we talk about the UL 3741 products that just came out and surprisingly allow 1000V within the array after shutdown!