A phase loss protection switch, also known as phase protection relay prevents three-phase motor failure due to line or motor overheating . The relays are designed to protect the devices with sensitive operation voltage against failures due to line voltage. Features: Three-phase-four wire: Yes Overvoltage protection: (1.05~1.30)×Us Phase failure protection: Yes Package Include: 1 x  NJYB3-9 Phase Loss Protection Switch