The NH system is classified among plug-in fuse systems and is composed of: fuse-base, (possibly including terminal covers and phase barriers), fuse-link with blade contact, fuse-link replacement device (LV HRC fuse puller). Since the design of this system cannot guarantee non-interchangeability of rated current, it must be handled by a qualified professional. NH-fuse links „gTr“ are used for the protection of transformers. The time/current characteristic is especially adapted to that of the protected transformer and implies optimal selectivity to NH-fuse links characteristic gG. The fuses can be loaded with 1,3 times nominal current for up to 10 hours. The fuse link operates at 1,5 times nominal transformer current within 2 hours. VDE 0636 Teil 201, IEC 60269-1 und -2.