A switch and a fuse are both connected in the live wire of a domestic circuit. The reason is that the live wire is the one at 230 V.
If a switch were in the neutral wire, switching the appliance off would break the circuit, but the appliance would still be connected to the live wire. Parts inside it would stay at about 230 V, and someone touching them could get a shock as current flows through them to the ground. A switch in the live wire disconnects the appliance from the live supply when it is off.
The same is true of a fuse. When a fuse in the live wire melts, the appliance is disconnected from the mains and the parts inside are safer to touch. A fuse in the neutral wire would melt and leave the appliance still connected to the live wire.
