Case study # 2.4 Title Damage on ISM (I-Interface Subscriber Module) Type of trouble Damage. Source of trouble Lightning. System affected Transmission equipment. Location Telecommunication centre. Keywords Damage, lightning surge. Version date 2004-01-01 System configuration A system configuration and an estimated current flow are shown in Figure 2.4-1. At a lightning stroke, a switching equipment ISM (I-interface subscriber module) on the second floor, was damaged and its operation was halted. An ISM equipment located on the first floor was not damaged. No other equipment, aside from the ISM was damaged, and there were no error messages except those of the ISM equipment. The ISM on the second floor was connected to two power equipments, D-SSF and F-SSF. The main power equipment is MR-48 on the ground floor, and the potential reference is a dc+ point in the MR-48. The current flowing through the ISM on the second floor followed a large loop, as shown in Figure 2.4-1. It is assumed that the equipment is easily affected by lightning. Radio tower Wave guide 2F CSM PDF CLK line DC+ DC power feeding line D-SSF ISM F-SSF DC+ F-SSF 1F ISM-0E TR DC+ DC BF EN-48-TH-RF MR-48-R2-RF DC+ DC+ DC+ Miti(08)_F2.4-1 E0 Figure 2.4-1 – System configuration Copyright © ITU 2010 – All Rights Reserved