The International Telecommunication Union (ITU) is a specialized agency of the United Nations devoted to international harmonization. The ITU Telecommunication Standardization Sector (ITU-T) produces the K series of recommendations covering protection against interference. Recommendations are nonbinding standards, which allows modifications to the recommendation to cover local conditions, such as testing with the local ac supply of 120 V rather than the recommendation value of 230 V. Most European countries recognize the ITU-T standards. The most recent revisions of ITU-T K.20 (February 2000) and ITU-T K.21 (October 2000) added technical requirements for coordination between the primary protectors and the secondary protectors. A previous article provided a thorough overview of the standards. This article examines the surge and power-fault requirements as called out in the updated ITU-T standards. A schematic solution for achieving compliance with these two standards is discussed in this article. Both ITU K.20 and ITU K.21 address the protection of telecommunications equipment. Such telecommunications equipment includes T1/E1 lines, x-type digital subscriber line (xDSL) technologies, integrated services digital networks (ISDN), Ethernet links, or just plain old telephone service (POTS). The physical location of the equipment determines whether K.20 or K.21 is observed.
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