Introduction to lightning and AC power fault surge protection for telecom signaling cables

This paper provides an introduction to the types of lightning surges and AC power fault surges that commonly affect the signaling cables of telecom network infrastructure and terminal equipment. Discussion is limited to twisted-pair copper lines such as telephone tip/ring cables and Ethernet cables. Surge types addressed include induced surges caused by nearby lightning strikes, induced AC voltages caused by fault conditions in adjacent AC power cables, and events caused by direct-contact with AC power mains. The basic physical mechanisms that cause each type of surge event are explained, with attention to both theoretical predictions and real-world measurements. Interactions between the surge energy source and the connected equipment will cause various types of surge waveforms to appear on the affected cables. The resulting surges are characterized for both outside cable plant and for cables routed entirely within a building. The ways in which various international testing standards attempt to simulate these surge events are described. Examples of some industry-standard test procedures and compliance requirements are presented. Some general guidelines are provided for evaluating the surge tolerance of a given design based on an analysis of the applied surge and the available paths for surge currents to flow. This type of analysis will often identify potential weaknesses based strictly on a review of the proposed design, prior to performing any actual surge tests.