600 V dc Time-Delay Fuses for Mines and Industry

All fuses used on dc circuits in mines must be approved by the Mine Safety and Health Administration (MSHA) and approval is based on meeting MSHA test requirements. All Underwriters Laboratories, Inc. listed 600 V time-delay commercial fuses are marked ``600V.A.C. or Less´´ and most do not meet MSHA requirements, unless modified. A simple modification is discussed, which makes UL listed time-delay fuses acceptable for mines and industrial dc applications such as overload and short-circuit protection for individual motors in a group of motors supplied by a single converter or adjustable speed drive.