Classification and Standardization of Cables and Limiters for Secondary Network Systems

As useful information for the proper operation of secondary network systems, the Limiter Task Group has prepared the information given in the Appendix. The temperature classification test procedure (current-loading test) provides the means for classifying a combination of cable insulation and sheath material as to its "damage temperature" for operation with limiters. Numerous insulation and sheath combinations have been classified by this procedure and the standard classes L260 and L220 have been adopted for those combinations of insulation and sheath whose damage temperatures are at least 260 C and 220 C respectively. Included in the L260 class are the mineral-base and GR-S rubber insulations of the RH-RW type with neoprene sheath and in the L220 class are the oil-base and butylrubber ozone-resistant insulation with neoprene sheath. A simple oven test has been devised for preliminary testing and initial comparisons, before final classification by the current-loading test. Insulation-damage curves for the operation of cable in duct, have been adopted for 4/ 0 through 1,000-MCM cable of the L260 class, and tentatively adopted for 4/0 cable of the L220 class. For proper co-ordination with the L260 class of cable, the time-current characteristics of the present limiters have been adopted as standard for the L260 class of limiters. For the L220 class, the time-current curve for the 4/0 L220 limiter, has been tentatively adopted. The limiter has been found to be very effective in preventing smoke, fire, explosion, and the spread of damage that might result from roasting of cable insulation.