INTERNATIONAL 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 potential rise due to power faults, direct contacts between telecommunication lines and power lines and electrostatic discharges. The sources for overvoltages in internal lines are mainly inductive coupling caused by lightning currents being conducted in nearby lightning strokes or lightning currents being conducted in nearby conductors. Major changes compared with the 2000 version of this Recommendation include: ? ? ? replacing the longitudinal test with a port to earth test; the introduction of an external port to port test; adding internal port requirements. Source ITU-T Recommendation K.21 was approved by ITU-T Study Group 5 (2001-2004) under the ITU-T Recommendation A.8 procedure on 29 July 2003. ITU-T Rec. K.21 (07/2003) i FOREWOR