The correct answer is: A. neutral wire
A fuse is a safety device that is used to protect electrical circuits from overloading. It is a small, cylindrical device that contains a metal strip that melts when the current in the circuit exceeds a certain value. This melting of the metal strip interrupts the flow of current and prevents the circuit from overheating.
The neutral wire is the return path for current in an electrical circuit. It is connected to the ground at the service panel, and it provides a safe path for current to flow back to the source. If a fuse were inserted in the neutral wire, it would not be able to protect the circuit from overloading. This is because the current would still be able to flow through the fuse even if the metal strip melted.
The other options are incorrect because they are all parts of an electrical circuit that can be protected by a fuse. The negative wire in a DC circuit is the return path for current, and the positive wire is the source of current. The phase wire is the live wire in an AC circuit.
In conclusion, a fuse is never inserted in the neutral wire because it would not be able to protect the circuit from overloading.