Class aR, gR and gS
Traditionally high speed fuses have only been used for short circuit protection, another device in the circuit protects against overload. Fuses only intended for short circuit protection are called class aR. Recent technological developments have made it possible to combine both short circuit protection and overload protection into the same fuse, class gR.
Class gR and gS offer superior protection compared to class aR. Class gR/gS fuses can often direct replace class aR fuses, however a class gR/gS fuse shall never be replaced by a class aR.