IEEE 1692:2011 pdf free download – IEEE Guide for the Protection of Communication Installations from Lightning Effects
High differential ground potentials between local equipment and remote power grounds make the powerservice conductors a favored discharge path for LGPR currents. Soil conditions have a significant effect ondifferential ground potentials. Higher soil resistivity will result in higher differential ground potentials fromlightning strikes to earth. With cloud to ground electric potentials in the magnitude of tens of millions ofvolts, an earth strike can be characterized as a current source. When the stroke discharge occurs the currenttraveling in the earth will flow regardless of the soil impedance.General application of ohm ‘s law willindicate the higher soil resistivity will result in a higher differential ground potential for a given dischargecurrent.
Sites without towers may experience LGPR effects as much, if not more, than sites with towers as they areless likely to have extensive grounding infrastructure.Sites at most risk are areas with a higher occurrenceof lightning and high soil resistivity.
5.1 Surge protective devices (SPD) and wire-line
The standard surge protective devices (SPD) in the telecommunications industry, for the termination ofcommunication wire-line services is the gas discharge tube(GDT).GDTs are also called gas tubes. GDTscan be found on virtually every telephone pair terminated in homes, buildings, and similar locations.GDTsare designed to shunt most current to ground. If the magnitude shunted does not exceed a certain thresholdthe SPD will help protect equipment, and personnel, from harm.
Most shunting devices,however，do not fully protect network electronic equipment from a GPR or“outgoing current,” whether induced from lightning or from a faulted power line. When shunting devicesare connected to an elevated ground (outgoing current) during a GPR event, they merely offer an additionalcurrent path off the site to remote carth (the other end).
When SPDs (GDTs,MOVs，ABDs,SCRs, SADs, SASs,etc.) are used as ground shunting devices,theywill not protect equipment from GPR. These devices merely offer an additional path to remote earththrough the communication pairs for any and all outgoing currents.
When there is a GPR event the SPD provides a connection of the communication path in the reversedirection from which they were intended to operate and increases the possibility of equipment damage totelephone and power installations.
The most susceptible locations are those where the equipment is located ncar, or under, towers andor arelocated at a higher altitude than the surrounding area.
Some of the susceptible locations to equipment damages include the Public Safety Answering Pointlocations(also called 911 PSAP). The typical 91l PSAP center is a relatively small building under, or near,a radio tower. This tower is a likely target for lightning.Personnel taking emergency calls coming into thePSAP may be at a higher risk since they must be at the phones at all times and cannot be off the phoncsduring lightning storms，as recommended in virtually every telephone book in the United Statcs. Foradditional information see ATIS 0600321 [B2].
Whether the site is a 911 PSAP center or a cellular telephone (radio) antenna on top of a mountain, specialprotection methods are available and must be used to reduce the risk of lightning damage to equipment andassociated working personnel.Methods will be presented in this Guide to enable engineers to incorporatethem into the general construction design.
Effective protection of sensitive equipment with SPD shunting devices is complex. A well-designedinstallation requires coordination of the protection for low-voltage power feeds (ac and dc)with theprotection for telecommunications facilities in order to minimize the effect of intrabuilding GPR.The useof secondary SPD is recommended to supplement the primary SPD (see ITU-T K.1l [B26]). Surgeresistibility and impedance of the terminal equipment must be compatible with the selected primary SPD.