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BX System Chassis

BX Ballasted Systems Listed to UL 3741

BX can now be installed without MLPE devices.

The IronRidge BX System is listed to UL 3741, in addition to UL 2703, offering more design flexibility. This includes the option to design without using MLPE devices, which can reduce material and installation costs. Refer to the BX Installation Addendum for instructions on how to design and build a UL-3741-compliant system.


A new safety standard, UL 3741, was published in late 2020. It is now referenced in the 2020 National Electric Code (NEC) 690.12 B (2) as another option to comply with rapid shutdown requirements inside the array boundary. IronRidge’s BX UL 3741, Photovoltatic Hazard Control System (PVHCS) listing, allows systems to be designed up to 1000V without the need for module-level power electronics (MLPE).


The BX Ballasted System is listed to UL 3741 and approved with select string inverters that incorporate safety requirements for rapid shutdown. Without the need for MLPE, system costs can be dramatically reduced, saving on materials, installation time, and future O&M costs, all while ensuring firefighter safety—as verified by the certification requirements of the UL 3741 standard.

BX Systems can now use a 1000-volt string inverter, saving several cents per watt and cutting the number of cable connectors in half. And less connections mean less points of failure. As an added benefit, the BX Chassis are polymer-based—so having less exposed metal edges will reduce the risk of wire damage that could cause a ground fault.


The Underwriter’s Laboratories (UL) is a standards development organization responsible for developing and writing the safety standards for the US. Certification for BX and other IronRidge systems are tested and listed to UL standards by Intertek, a nationally-recognized testing laboratory. For more information on how installers can design projects to comply with this new safety standard, UL 3741, review the uses cases and addendum that are referred to below.

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