Ampacity Calculation for DLO Cable Used in Permanent Installations

DLO is a railroad industry designation given to flexible cables certified for use in diesel locomotives. For use outside the railroad industry, these cables may be labeled with a UL insulation-type certification such as RHW-2. Carried over from the cables' railroad lineage are sizes such as 535 kcmil that are absent from NEC tables. While interpolation of NEC tables may appear as a logical means of calculating ampacity, the NEC limits ampacity calculation options to the formula provided in 310.15(C). Applications of the 310.15(C) formula for cables in underground duct banks are well documented, but constants for duplicating conditions of NEC Table 310.16 are absent from the NEC. For application of nonstandard cable sizes in conditions matching those of NEC Table 310.16, this paper provides ampacity calculations while also clarifying the delineation between permanent building wiring and temporary cords as defined by the NEC.