This is a special design foot switch with two stage momentary contacts.There are noticable resistance between stage one and stage two when pressing the pedal without reaching the pressure point,the foot switch operates in the normal model.In case of emergency,the user depresses the foot pedal even harder instead of releasing the pedal.This special safety foot switch will break electrical contact and locked.The manual reset button need to be pushed before it can operate in normal model.This can quickly prevent damage to the machine or injury to human life.