ITU-KINTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU K.21 (07/2003) SERIES K: PROTECTION AGAINST INTERFERENCE Resistibility of telecommunication equipment installed in customer premises to overvoltages and overcurrents ITU-T Recommendation K.21 ITU-T Recommendation K.21 Resistibility of telecommunication equipment installed in customer premises to overvoltages and overcurrents Summary This Recommendation specifies resistibility requirements and test procedures for telecommunication equipment which is installed in or on a customer premises building. Overvoltages or overcurrents covered by this Recommendation include surges due to lightning on or near the line plant, short-term induction from adjacent a.c. power lines or railway systems, earth ……