International Appliance Manufacturing 2008 - (Page 36) Coordinated Circuit Protection for Electric Motors, Transformers and Control Units in Home and Professional Appliances Faraz Hasan, Global Industrial & Appliance Marketing Manager, Tyco Electronics Corporation/Raychem Circuit Protection Products The electric motors, transformers and controllers used in home and professional grade appliances are often subjected to mechanical overloads, overheating, stalls, lost neutral, severe overvoltages, humidity and other damaging factors. New polymeric positive temperature coefficient (PPTC) devices are designed for operation at line voltages of 120 VAC and 240 VAC, and can help appliance designers prevent safety and fire hazards, as well as reduce warranty return and replacement costs resulting from motor failure. Protecting increasingly sophisticated and complex control boards from misconnection, power surges or short circuit damage is of particular concern to the equipment manufacturer. Although appliance transformers, their enclosures and connections are capable of withstanding higher voltage transients, the use of sensitive solid-state devices on the board necessitates improved overcurrent, overtemperature and overvoltage control. Coordinating overcurrent and overvoltage protection can also help designers comply with safety agency requirements, minimize component count and improve equipment reliability. A metal oxide varistor (MOV) overvoltage protection device, used in a coordinated circuit protection strategy with a line-voltage rated PPTC overcurrent device helps manufacturers meet IEC 6100-4-5, Resettable circuit protection devices can be used to help provide overtemperature, overcurrent and overvoltage protection for the electric motors and fans, controllers, touchpads, displays and interface circuitry required by sophisticated appliances. 36 International Appliance Manufacturing 2008
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