Red Seal Electrician Practice
Wiring and componentsQuestion 810 of 1506

Why does a thin conductor have a lower current rating than a thick conductor of the same material?

  1. Less resistance per metre, so the voltage drop is too small.
  2. Thin copper cannot carry magnetic flux as well.
  3. More resistance per metre, so more heat.
  4. Its insulation is always thinner, so it flashes over at low voltage.
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Correct answer: More resistance per metre, so more heat.

Resistance per unit length rises as the cross-section falls. More heat per ampere means a lower safe current.

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

Practice wiring and components

Questions last reviewed: 18 October 2026