ISDN and DSL installations allow fast transfer of large amounts of data. The drawback is that surges can also rapidly reach the terminal device and damage computer equipment. The danger can be overcome by balanced use of basic and precision protection devices. Basic surge protectors where the data lines enter the building divert all harmful partial lightning currents.Precision surge protectors filter out capacitively and inductively coupled-in voltages directly at the terminal device. Surge protector for RJ5 especially well suited for use in ISDN installations, having gained certification of trouble-free operation in