Lightning surge damage to Ethernet and POTS ports connected to inside wiring

Abstract

In recent years, many suppliers of telecom equipment have reported higher than expected rates of lightning damage to Ethernet and POTS ports connected to cables located entirely within the same building. There are three known mechanisms by which lightning surges can be coupled onto inside wiring, but these mechanisms are statistically infrequent. Given the reported rates of surge damage, these known mechanisms do not provide a simple explanation. It appears that additional surge coupling mechanisms may be involved. The three known mechanisms are described, and it is shown that surge damage from these mechanisms should be infrequent. Three new theories for additional coupling mechanisms are then described. All three of these new theories are based on the notion that surges appearing on the AC mains outlets in the building are being coupled onto inside wiring communication cables. The analysis suggests that the first of these additional coupling mechanisms seems an unlikely cause for the apparent increase in surge failures. The second mechanism appears more plausible, particularly because it correlates to the recent industry trend of implementing wall mount Class II AC mains power supplies as switching converters rather than traditional linear supplies. However, the theory behind this second mechanism only applies to surge failures of Ethernet ports. A third potential mechanism is based on unintended side effects of consumer grade multi-port surge protectors used in installations with poor grounding. This mechanism applies to both Ethernet and POTS failures. Further study will be necessary to determine whether any of the three additional mechanisms are in fact the cause of the apparent increase in field failures. In the meantime, some guidelines are presented for manufacturers who wish to implement enhanced surge protection on Ethernet and POTS ports that connect to inside wiring.