The D fuse system is a first generation screw fuse system. It is still widely used in systems. The D fuse system is used in low-voltage systems in which the fuse inserts are accessible to laymen and can be replaced by them. The D fuse range includes the sizes NDZ, DII, DIII, DIV and DV. D fuse bases with D fuse inserts of operating class gG are used to protect cables and systems. D fuse inserts safely switch off impermissible overcurrents and short-circuit currents up to the nominal breaking current. They also protect electrical devices and systems from the electrodynamic effect of high short-circuit currents. DIN VDE 0636-3. The D retaining chuck enables the use of DII fuse inserts in DIII bases.