- 3UA thermal relay is suitable for using in power system with AC 50Hz, rated operation voltage up to 660V and 1000V, in main circuit, current from 0.1A to 630A. It is used to protect AC three - phase asynchronous motor against overload and open-phase. - - The current setting value can be regulated and the setting current values of many thermal elements are intercrossing overlepping arrangement, for easy selecting by the customers from －25°C to +55°C air temperature as the products have temperature compensating. The relays have the test push-button for breaking NC contacts, the operating indication and free trip characteristics. The items conform to IEC292-1, IEC337-1 & VDE0660.