Case study # 2.10 Title Protection of a wireless service connected to a few kilometres of copper cable Type of trouble Damage. Source of trouble Lightning. System affected Access switch. Location Outdoors (On a pole in a rural area). Keywords Damage, lightning surge, protection coordination, GDT, solid state overcurrent protection. Version date 2004-01-01 System configuration The antenna and the electronics containing the subscriber line interface circuit (SLIC) of a wireless service are normally mounted on the side of the customer's house or on a pole within a few metres of the house. In some installations, where the house is not in line of sight with the radio base station, the antenna and electronics may be installed a few kilometres from the house. When this type of installation is used in a lightning-prone area, lightning protection is installed to protect the electronics. In this case, although gas discharge tubes (GDTs), and in some installations GDTs plus positive temperature coefficient (PTC) type overcurrent protection, were installed, lightning damage still occurred regularly (see Figure 2.10-1). Protected termination module GDTs Pair 1 to building Pair 2 to building Antenna and electronics Power supply 0V V d.c. Earth Earth bolt Earth reference via power supply Mounted at top of pole Mounted on pole 1-3 m above ground Miti(08)_F2.10-1 Figure 2.10-1 – Original system configuration Copyright © ITU 2010 – All Rights Reserved