The Electronic Fusible Link (EFL) is a heat responsive deivce used with the Siemens OpenAir UL listed fire and smoke control damper actuator. Upon exceeding the 350F (177C) temperature limits of the EFL model ordered and installed, the EFL cuts power to the electronic damper actutor and the actuator's spring retrun mechanism closes the damper. The EFL is compatible only with OpenAir GNDxxx.xU/F UL listed fire and smoke damper actuators.The EFL must be factory-installed. The UL rating carried by the specific damper and actuator is assigned as an assembly and cannot be added in the field.