Underwriters Laboratories (UL® ) Certification for PTC Heaters:

For PTC thermistors that are to be used as self-regulating heaters, it is now possible to obtain UL recognition for a variety of parts. UL recognition of ceramic PTC devices is listed under the heading XPGU2 Component - Thermistor Type Devices. Thermistors Unlimited is listed under file number E157106. Within this classification,  a wide variety of PTC thermistors can be recognized. Both disc and rectangular styles can be listed. In addition, a wide variety of switch temperatures (Ts), R25 values, and voltage ratings can be recognized. Because the testing has been completed for a "family" of parts, as long as the new thermistor falls within the parameters of the parts that were tested, TU can immediately assign UL model numbers based on the part parameters.