WEB EXCLUSIVE: DSM Engineering Plastics, Birmingham, Mich., says the recent change to a UL standard covering low-voltage switchgear (LVSG) has opened up the way for engineering thermoplastics to replace thermosets in electrical applications such as miniature circuit breakers (MCBs). The UL 1077 standard for supplementary protectors used in electrical equipment is widely applied in the U.S. and South America. Before the recent update, applications such as MCBs in the Americas limited penetration by plastics other than thermosets such as polyester bulk molding compound (BMC). This revision also signals a continuation in the convergence of UL and International Electro-technical Commission (IEC) standards, which will make it easier for suppliers to supply the same product globally. (IEC/EN 60947 is the standard for LVSG in Europe, Asia, and elsewhere.)
With the change in the standard, materials with a Glow Wire Flammability Index of at least 750 C (according to IEC/EN standard 60695-2-12) can now be used for these supplementary devices. Glow-Wire End-Product testing (GWEPT) is no longer required, and a material can now be approved based on UL Yellow Card GWFI listings.
DSM, which supplies electrical compounds based on resins such as nylons 6 and 46, says manufacturers and users of MCBs will benefit because production of MCBs in engineering plastics is more cost-effective than with thermosets. For example, cycle times are at least 40% shorter than for BMC, material wastage is reduced, recycling is much simpler, and more innovative product design can be used for example in thin-walling and integrating additional functions into the housing of the device. Housings in engineering plastics are also more robust, since the materials are more ductile than thermosets, says DSM.