Question

A fuse should always be placed in the _______ wire of a mains circuit.

Answer 1

An electric fuse is one of the most commonly used components in the electrical circuit. It is used for safety purposes. The electric fuse is composed of a specially designed wire, which does not have a very high melting point. Whenever the current exceeds the safety limit, then there are very high chances that the appliances attached may get damaged.

Complete answer:
An electric fuse interrupts the flow of current in the electric circuit. Its main purpose is to block the flow of current which is greater in magnitude then the prescribed. It is a short piece of wire. The wire has high resistivity and very low melting point. And it melts down easily whenever the current exceeds the prescribed limit, due to the heating effect of the current.
Thus, to achieve the desired purpose of putting the fuse, it must be attached to live wire.

So, the answer is live wire.

Additional Information:
The fuse also prevents any damage that could otherwise happen to the electric circuit.

Note:
One thing to keep in mind is that the fuse must be attached to the circuit in such a manner that the current coming in must first pass through the fuse and then after to other appliances, if this is not the case then the purpose of putting in the fuse gets defeated.
The resistance of the fuse wire is greater than that of the live wire.