Temperature limit of coil Q) To which class of insulating material are the solenoids coils of contactors have to subject? What are their maximum permissible temperatures? ANSWER: The maximum permissible temperature of solenoid coils of contactors is 140 °C. Example: Siemens make 3TF,3TH contactors coil sustain upto 140 degree C. For these coils the maximum permissible temperature rise limit for coils in air according to class of insulating material is E = 100 K. Since this is a temperature rise in Kelvin, this value shall be added with the maximum ambient air temperature of +40 °C of the contactors as described in IEC 60947-4-1. The temperature rise limits applicable only if the ambient air temperature remains within the limits -5 °C to +40 °C. ......