Fuses break circuits to prevent damage from excess current

Steps:

• Identify the fuse's role: it melts when current exceeds safe levels.
• Recall that fuses are in series with the live wire in plugs.
• Understand overloads cause overheating in wiring if unchecked.
• Conclude the primary goal is wiring protection, not user safety directly.

Why D is correct:

• A fuse is a safety device that melts at high current (per Ohm's law, I²R heat), interrupting the circuit to prevent wiring from overheating and causing fires.

Why the others are wrong:

• A: Earthing connects metal parts to ground, not the fuse's function.
• B: Fuses protect circuits, while earthing and insulation primarily prevent shocks.
• C: Earthing the plug involves ground wire, separate from the fuse.

Final answer: D