Definitely not. Apart from a general use safety point, during trouble shooting me must disconnect the mains.
Depends on the type of fuse. Most daily use fuses are in a transparent glass tube. We will see a black shiny deposit inside the tube if the fuse is blown. This is caused by large fault current causing the fuse wire to melt and explode with splatter. However often the fault might cause the fuse to melt much slower and merely break without any splatter. In such a case we have to either try and see the thin wire or use a multimeter’s ohms range to check. A good fuse will show a short.
The fuse prevents a fire being caused under a fault condition. High current flows caused by component failures produces extreme heat. This can set afire wire insulation and anything else that happens to be in contact. A fuse ruptures in a few seconds when it’s rupture current is reached. Note that the operating current is far lower than the rupture current. A 1A fuse does not rupture at 1A but at a substantially higher current, usually at 250%. Also a 1A fuse is operated at 70% i.e. .75A. IF you do operate it at 1A it will blow perhaps after several hours of use.
Fuses are also of different rated speeds- superfast, fast, slowblo, normal, PTC. PTC fuses do not normally rupture but provide a high resistance until the current drops substantially and the PTC fuse cools.
Fuses have a maximum rated voltage. You can operate below the rated voltage, but never above.
See the attached sheets.
Littelfuse_Fuse_322_332_Datasheet.pdf.pdf (805.0 KB)