Safety capacitors have a similar material set as regular capacitors, but they have unique designs that allow them to withstand harsh electrical conditions. They are tested by independent agencies like UL or CE, among others. IEC classifications are used to organize them by application and by the amount of electrical stress that they can withstand; the application classifications are X and Y. X capacitors are meant for line-to-line or across-the-line filtering, and Y capacitors are meant for line-to-ground or line bypass. The number 1 denotes the highest level of transient overvoltage capability in each subclass.