UL certifications for winding wires can be confusing for those that don’t deal with safety certifications on a regular basis. This article will attempt to clarify what those certifications mean and how winding wires can be used based on those certifications.

UL certifications for winding wires can be broken down into three basic categories:

  • OBMW2 Certifications, which cover non-served and served magnet wires and Litz wires
  • OBJT2 Certifications, which cover Single- and Multi-layer Insulated Winding Wires
  • OBJS2 Certifications for Electrical Insulation Systems (EIS)

OBMW2 certifications are the simplest of the three categories to understand. OBMW2 certifications cover UL recognized magnet wires and bare or served Litz wires. These winding wires can be found in an EIS as “Enameled Wire” and require additional ground and interleaved insulations. Rubadue Wire is a manufacturer of UL recognized OBMW2 products certified under file number E190291.

OBJT2 certifications cover insulated winding wires with certification to UL 2353. Insulated winding wires having UL OBJT2 certification can be used without additional ground or interleaved insulations. Rubadue’s UL file for insulated winding wires is E206198.

UL OBJT2 certifications are the most complicated and can be further broken down into certifications to UL 60950-1, UL 60601-1, UL 61558-1, and/or UL 61800-5-1.

Standard Equipment Covered
UL 60950-1 ITE (Consumer Electronics)
UL 60601-1 Medical Equipment
UL 61558-1 General Purpose Transformers & Power Supplies
UL 61800-5-1 Variable Frequency Drives

Certification to UL 60950-1 is mandatory for UL OBJT2 products. UL 60950-1 has the least stringent requirements of the standards in the group. Certification for winding wires to the other standards listed is optional and comes with mores stringent testing requirements. ANSI UL 62368-1 will eventually replace UL 60950-1 for insulated winding wires used in consumer electronics.

Insulated winding wires having temperature ratings >105°C must also be tested as part of an EIS.

Voltage ratings can be different for the different standards that a single wire is certified to. Check the manufacturer’s UL OBJT2 file to see if their UL certifications meet your requirements.

OBJS2 certifications cover Electrical Insulations Systems (EIS’s). An EIS is a combination of materials that UL has tested and found to be chemically compatible with one another. An EIS can include bare and insulated winding wires, ground and interwinding insulations, tapes, core tubes and bobbins, spacers and wedges, varnishes, etc. Transformer manufacturers can elect to adopt an EIS to cut down on their certification costs. For details on EIS adoption, see the article on UL’s website below.


Rubadue Wire maintains two Class F Electrical Insulation Systems with UL under file number E188330. These system designations are RXT-2 and TCA. They are available for adoption at no charge from us.

Questions about the contents of this article, Rubadue’s UL and VDE certifications, or Rubadue’s product offerings? Contact our knowledgeable sales and engineering teams to discuss your application at sales@rubadue.com or +1(970) 351-6100.