P6002ACMC datasheet(188/212 Pages) TECCOR

188 / 212 page

Telecommunications Protection

http://www.teccor.com

5 - 26

+1 972-580-7777

SIDACtor® Data Book and Design Guide

Telecommunications Protection

Because early telecommunications equipment was constructed with components such as

mechanical relays, coils, and vacuum tubes, it was somewhat immune to lightning and

power cross conditions. But as cross bar and step-by-step switches have given way to more

modern equipment such as digital loop carriers, repeater amplifiers, and multiplexers, an

emphasis has been put on protecting this equipment against system transients caused by

lightning and power cross conditions.

Lightning

During an electrical storm, transient voltages are induced onto the telecommunications

system by lightning currents which enter the conductive shield of suspended cable or

through buried cables via ground currents.

As this occurs, the current traveling through the conductive shield of the cable produces an

equal voltage on both the Tip and Ring conductors at the terminating ends. Known as a

longitudinal voltage surge, the peak value and wave-form associated with this condition is

dependent upon the distance the transient travels down the cable and the materials with

which the cable is constructed.

Although lightning-induced surges are always longitudinal in nature, imbalances resulting

from terminating equipment and asymmetric operation of primary protectors can result in

metallic transients as well. A Tip-to-Ring surge is normally seen in terminating equipment

and is the primary reason most regulatory agencies require telecom equipment to have

both longitudinal and metallic surge protection.

Power Cross

Another system transient that is a common occurrence for telecommunications cables is

exposure to the AC power system. The common use of poles, trenches, and ground wires

results in varying levels of exposure which can be categorized as direct power cross, power

induction, and ground potential rise.

Direct power cross occurs when a power line makes direct contact to telecommunications

cables. Direct contact is commonly caused by falling trees, winter icing, severe

thunderstorms, and vehicle accidents. Direct power cross can result in large currents being

present on the line.

Power induction is common where power cables and telecommunications cables are run in

close proximity to one another. Electromagnetic coupling between the cables results in

system transients being induced onto the telecommunications cables, which in turn can

cause excessive heating and fires in terminal equipment located at the cable ends.

Ground potential rise is a result of large fault currents flowing to Ground. Due to the varying

soil resistivity and multiple grounding points, system potential differences may result.

P6002ACMC датащи(PDF) 188 Page - Teccor Electronics