Royal DSM, a Material Sciences company based in the Netherlands, says a recent change to an Underwriters Laboratory (UL) standard covering low-voltage switchgear (LVSG) has opened up the way for plastics in electrical applications such as miniature circuit breakers.
The UL 1077 standard, for supplementary protectors used in electrical equipment, is widely applied in the US and South America. In Europe, Asia and elsewhere, IEC/EN 60947, a standard for LVSG and related industrial control gear published by the International Electro-technical Commission (IEC), is more prevalent.
The recent change in the UL will make it possible for engineering plastics to be used in applications such as miniature circuit breakers (MCBs) in the Americas, where until now it was hardly possible to use materials other than thermosets, according to DSM. This change also signals a continuation in the convergence of UL and IEC standards, which will make it easier for suppliers to supply the same products globally.
UL 1077 sets requirements on, among other aspects, the flammability of materials used in supplementary devices, which include MCBs, providing protection against overcurrent, or over- or under-voltage within electrical equipment. In the previous version of the standard, it was compulsory for materials to have a certain combination of flammability and ignition characteristics (UL 94 rating/hot wire ignition (HWI)/high current arc ignition (HAI)) at the minimum application wall thickness.
As said, following the change, materials with a Glow Wire Flammability Index of at least 750°C (according to the 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.
MCB producers and users will benefit because production of MCBs in engineering plastics is more cost-effective than in thermosets such as polyester bulk molding compound (BMC). According to DSM, cycle times can be trimmed by at least 40%, material waste is reduced, recycling is simpler and design freedom is enhanced. Housings in engineering plastics are also more robust, since the materials are more ductile than thermosets.
“The change in UL 1077 will spur growth in the LVSG market as innovative product suppliers take advantage of the new design freedom it offers, and the opportunities it provides for them to cut costs and increase sustainability. DSM, with our understanding of the application requirements in combination with our engineering plastics expertise, will continue to support our customers globally with our broad portfolio, including our Stanyl polyamide (PA) 46, and new halogen-free flame-retarded grades of our Akulon polyamide 6.” says Peter Dufour, Global Marketing Manager – Electricals with DSM.