... TN-C.TT,IT etc. Voltage surge protective deviceLY series surge protective device (SPD) is usually be used in the IT, TT, TN ... . SPD has two protection modes: MC and MD, SPD is in compliance with GB18802.1/IEC61643-1 standards.Working principle1.SPD ... being electric touching, indoorfixedly mounted, limiting voltage.2.SPD has built-in disconnector, when SPD is invalid due to overheating or breakdown, the ...