Faults in Surge Arresters occur due to insulation degradation and imperfection, corona , aerosols and moisture. Although the surge arresters are cheap to replace, troubleshooting and finding faults in surge arresters is nearly important as the equipment they are protecting. Most of the surge arresters nowadays have counters which can help in some lifetime calculation, but the real condition of the Surge arrester is the one you have tested. The most common test of surge arrester is leakage current measuring (on the grounding point) with 3rd harmonics analysis. The SLCM does constant monitoring on leakage current and harmonics analysis with wireless comunication and most advanced notifications and trending.