| The problem is usually related to the short circuit current. Regardless if you have there 1 or 10A fuse, during a short circuit event the current is limited only by the wiring resistance. It does not depend on the upstream fusing either, just the impedances. The fuse may evaporate it's filament, but an arc set there in and continues to carry the current, until it get extinguished. And the problem is, higher the current, better the arc holds on and more energy it dissipates. So to have the fuse really working, the internal fuse design has to be able to extinguish that arc. The maximum short circuit current the fuse is designed to interrupt is called the current breaking capability. It means, the fuse could be used only in circuit with the short circuit current lower than the rated limit, otherwise it is not guaranteed the fuse will be able to interrupt the current (and do not pose a fire hazard on it's own).
And don't forget, the current breaking capability is linked to the system voltage (higher the voltage, harder to extinguish the arc). With 12V or 24V car installation, the voltage can not support any arc, therefore the fuses could be so simple as a wire in the air (just the cathode fall on the arc tends to be higher). But with the mains you have plenty of voltage, so need really good arc quenching.
With the 50A circuit, I would expect short circuit currents up to the 10kA range, so you would need a fuse rated for at least 10kA breaking capability at 250VAC.
That are not the glass instrument fuses (they have current breaking capability of about 20A, so useless on any mains), but virtually only ceramic body and sand filled ones (e.g. those BS1362 specified for the British mains plugs).
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