DC overcurrent protection-Where we stand

The procedures used to determine the DC ratings for fuses and the issues pertinent to ensuring a proper DC fuse application are discussed. For a better understanding of how fuses are rated for DC, Underwriters Laboratories UL Standard 198L is examined. The standard defines the requirements and test procedures for DC-rated Class H, CC, G, J, K, L, R, and T fuses for industrial use in accordance with the National Electrical Code, NFPA 70. The overload test, interrupting ability test, and maximum energy test in the UL standard are discussed. UL Standard 198M, which covers Class K and R fuses intended for use in protecting trailing cables in DC circuits in mines, is also examined. The overload and short circuit requirements are given. The derating of DC voltage ratings to about 1/2 the AC rating to meet the requirements in UL standard 198L or M is considered.<>