A special Nylon film which reacts to ambient humidity is built into the Humidistat. Change in size of Nylon film activates a switch mechanism to turn the system on and off.  Widely apply in both household and industrial environmental control system to monitoring and controlling humidity – household humidifier, dehumidifier, HV,MV or LV Switchgear, Transformer Substation, Off-grid System, Cable Branch Box, …etc. Proper control of humidity can effectively prevent electrical breakdown due to dew or high humidity.