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DuPont Zytel nylon housing high-performance circuit breakers

Du Pont Engineering Polymers : 18 June, 2007  (Technical Article)
Square D Company is achieving benefits of easier field installation and lower manufacturing costs with the adoption of DuPont Zytel nylon as housings for high-performance circuit breakers. With a base and cover molded from a tough, strong, high-voltage-resistant grade of Zytel, the housings mark a trend-setting step away from traditional thermosets for such parts.
DuPont Zytel nylon provides rugged protection for certain high-interruption-rated models of Square D’s PowerPact line of circuit breakers, namely H- and J-frame products for 70 to 250 A (ampere) applications.

“Zytel nylon allowed us to develop a housing design with integrally molded features allowing snap-in installation of terminals and accessories,” said Bill Stewart, product manager, Power Protection at Schneider Electric, the parent company of Square D. “The snap-in design saves time and money during in-the-field configuration of circuit breakers for different applications,” he added. Such features are difficult or impossible to create with thermoset designs owing to their greater stiffness and wall thickness.

The use of Zytel also provides savings in manufacturing costs, according to Stewart. Additional integrally molded features reduce total part count and simplify assembly. Faster cycling and recycling of sprues and runners during molding also save costs compared with thermoset parts.

The housings mark a major advance for thermoplastics in applications requiring high short-circuit ratings. The circuit breakers on which they are used pass stringent electrical testing to comply with requirements of the 2005 National Electrical Code, including a 100 kA (kiloampere) short-circuit rating at 480 Vac (volts, alternating current) per UL489. Housing parts made of most flame-retardant thermoplastic resins fail this demanding test.

DuPont developed a special nylon resin, Zytel FR82G33V1, to meet these stringent test requirements while also delivering excellent mechanical strength, toughness and processing productivity. Based on a PA66/PA6 copolymer with 33 percent glass-fiber reinforcement, the resin delivers a combination of other desirable properties including a V-1 UL94 flame classification and excellent tracking resistance, toughness, strength, and molding productivity.

Square D benefited from solid technical support from DuPont in developing the housings. DuPont specialists provided crucial support in three areas: 1) by developing a material to meet application needs; 2) by working closely with Underwriters Laboratories on testing and approval; and 3) by supporting Square D's molder during process startup and optimization.

Square D PowerPact circuit breakers using Zytel are available in H- and J-frame models with a multitude of configuration options. They are certified to global standards including UL, IEC, CSA and NOM, according to Square D.

DuPont is a science-based products and services company. Founded in 1802, DuPont puts science to work by creating sustainable solutions essential to a better, safer, healthier life for people everywhere. Operating in more than 70 countries, DuPont offers a wide range of innovative products and services for markets including agriculture and food; building and construction; communications; and transportation.
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