Appliance Design - February 2008 - (Page 50) CORDS STOPPING STRAIN A strain relief bushing from Heyco. A variety of Interpower strain reliefs including flex, dome, multi cable and liquid seal. Protecting power cords necessary to protecting people. W by larry adams 50 applianceDESIGN February 2008 hether the appliance is a vacuum cleaner or a floor scrubber, hair dryer or curling iron, microwave or refrigerator, they all have at least one thing in common, the power cord. And, where there is a power cord, there usually is a need to protect it. Strain reliefs can do just that. They are designed to allow the cord to move without damaging it or the wires inside the cord. They can be used at the plug end, where the cord goes into the wall receptacle, or at the equipment end, where the cord meets the appliance. It is at the two ends of a flexible cord that strain relief is most needed – the transition points where the cord changes from flexible to rigid. Whether as a separate component or a molded-in feature, a strain relief is designed to protect the cables from damage from abrupt pulls or pushes, and excessive flexing. With stranded conductors, if one wire breaks under the strain, the other wires inside the cord have to carry the additional load. That creates additional heat at the junction where the cord is flexing and could cause catastrophic problems such as a fire, short circuit or electric shock to the user, says Larry Oden, engineering manager of Unicable, a cordset supplier in Bowling Green, Ky. “If you bend a wire back and forth it will fracture and break,” he says, “that is a metallurgical fact of life with the copper wires.” When the wire breaks, an internal arcing can occur which is a “real concern for irons and hair dryers and those kinds of devices because that arcing can cause physical injury,” says Oden. There are several types of strain relief on the market. Many companies such as Interpower Corp. of Oskaloosa, Iowa, offer what are called dome nut and flex style reliefs. Other companies such as Heyco Products of Toms River, N.J., a supplier to cord vendors www.applianceDESIGN.com http://www.appliancedesign.com
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