UL 497A ISBN -7629-0626-X Secondary Protectors for Communications Circuits MARCH 20 .2001 -UL 497A Underwriters Laboratories Inc .( UL) 333 Pfingsten Road Northbrook .IL 60062-2096 UL Standard for Safety for Secondary Protectors for Communications Circuits ,UL 497A Third Edition ,Dated March 20 ,2001 UL is in the process of converting its Standards for Safety to the Standard Generalized Markup Language ( SGML),and implementing an SGML pliant document management and publishing system .SGML an international standard ( ISO8879-1986 )-is a descriptive markup language that describes a document's structure and purpose ,rather than its physical appearance on a page .Significant benefits that will result from UL's use of SGML and these new systems include increased productivity ,reduced turnaround times , and data and information consistency ,reusability ,shareability ,and portability .However ,the fonts , pagination ,and general formatting of UL's new electronic publishing system differ from that of UL's previous publishing system .Consequently ,when revision pages are issued for Standard with the new publishing system ,these differences may result in the printing of page...
UL 497A-2001 通信电路的辅助保护装置.pdf
