Higher fuse rating allows circuit overload

Steps:

• Original fuse (10A) matches safe circuit current for heaters.
• Replacing with 20A fuse permits double the safe current without blowing.
• Heaters draw 20A total when switched on, exceeding wire rating.
• Mains wiring overheats due to excessive current.

Why C is correct:

• Ohm's law (I = V/R) shows fixed load resistance draws twice the rated current if voltage is standard, but higher fuse fails to protect underrated wiring from I²R heating losses.

Why the others are wrong:

• A: Heaters receive fixed current based on resistance, not halved by fuse.
• B: Individual heaters don't double current; total circuit does, but fuse allows it.
• D: 20A fuse withstands the 20A draw without melting.

Final answer: C