Both car fuses and house fuses are installed to protect the wiring - fuses inside equipment are instaled to protect the equipment itself. If too much current flows something (the wires) may get very hot and catch fire - car (or house) destroyed.
Fuses sometimes blow spontaneously because they get "tired" but it's quite rare - the usual cause of a fuse blowing is a fault. It seldom hurts to replace a blown fuse to see what happens but the general case is that the new fuse will also blow - indicating a fault.
It's not wise (potentially dangerous) to uprate a fuse to solve a problem.
To work out the current it helps to know the wattage of the equipment - divide total wattage on the circuit by voltage - a maximum load of 50W in a car for instance will draw 4.17 Amps so a 5A fuse should be OK.
60W in the home (230v) will draw just 0.26Amps so a 1A fuse will do but people usually use a 3A fuse for a 60W table lamp because 1A fuses are a bit difficult to find.
It is not unusual for a failing lamp fillament to cause a fuse to blow as small pieces of broken fillament fall across the supporting wires in the bulb.
Peccavi
March 2010
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