The main function of a fuse is to protect the electrical appliances connected in a building from damage by blowing out under faulty or high voltage condition. The fuse is always provided on the phase wire which carries the line current.
If the fuse is provided on the neutral wire instead of phase wire, then during abnormal conditions, tough the fuse wire melts and blows out, the appliances are still connected to the live wire and in case of leakage of any sort, some trouble will arise and cause damage to the appliance.
If the fault is on the neutral wire between the lamp and the fuse provided in it, the fuse will burn off because the neutral wire is at slightly higher potential w.r.t earth and thus the fault current will flow through the neutral wire and the fuse wire blows out.
But even then, current will flow through the live wire. This will cause considerable damage to the wiring and the appliances. So, for these reasons, fuse is always provided in phase and never on neutral!!
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