... , if one or more modules of SPD is invalid. LYD5-100 SPD is suit-able for the IT, TT, TN-C ... device, it is category B surge protective device.Working principle1.Fast response time: less than 25ns2.Low limited voltage3.Large current carrying ... color, invalid state: red color5.Kelvin wiring mode available. LYD5-100 Surge protective device(SPD)