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IEC 60245-1 Ed. 4.1 b:2008
Rubber insulated cables - Rated voltages up to and including 450/750 V - Part 1: General requirements
"Applies to rigid and flexible cables with insulation, and sheath if any, based on vulcanized rubber of rated voltages Uo/U up to and including 450/750 V used in power installations of nominal voltage not exceeding 450/750 V a.c. The particular types of cables are specified in IEC 60245-3, IEC 60245-4, etc. The code designations of these types of cables are given in Annex A. The principal change with respect to the previous edition is the replacement of insulation IE 1 with IE 4. "
International Electrotechnical Commission [iec]