Red Seal Electrician Practice
Wiring and componentsQuestion 808 of 1506

Copper melts at a very high temperature. Why is the ampacity of an insulated conductor still set by the insulation?

  1. The insulation fails at a far lower temperature.
  2. Copper loses its conductivity as soon as it warms above room temperature.
  3. Insulation adds resistance that the copper cannot carry.
  4. Copper expands and splits the insulation at rated current.
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Correct answer: The insulation fails at a far lower temperature.

The insulation is the weakest part. Its temperature limit, not the melting point of copper, sets the practical current rating.

Source: Lessons in Electric Circuits I: DC (Kuphaldt), 12.3: Conductor Ampacity

Practice wiring and components

Questions last reviewed: 18 October 2026