A wire that is not large enough to carry the electrical current passing through it will _________.

• A. Trip a breaker
• B. Overheat
• C. Melt insulation
• D. Glow

Answer: (B)

When a conductor is too small for the current, it heats up. The heat produced in a wire is proportional to I²R, so a smaller wire has higher resistance for a given current, and thus more heat is generated. This extra heat causes the temperature to rise, which is why overheating is the immediate consequence. If the heating continues, insulation may eventually melt or be damaged, but the direct result of an undersized wire carrying that current is overheating. A breaker tripping is a protective action that may happen because of the overload, but it’s not the wire’s inherent behavior; glowing is unlikely unless the wire becomes extremely hot.