Red Seal Electrician Practice
Wiring and componentsQuestion 616 of 1506

Why do some appliances have polarized plugs, with one prong narrower than the other?

  1. So the appliance can work on both DC and AC supplies.
  2. So the plug cannot be put in backwards.
  3. So the appliance runs at a higher voltage than a normal one.
  4. So the plug can be fitted into a two-prong adapter more easily.
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Correct answer: So the plug cannot be put in backwards.

A plug that fits only one way keeps the internal wiring in a known order, so the hot conductor is always the one the designer expects.

Source: Lessons in Electric Circuits I: DC (Kuphaldt), 3.8: Safe Circuit Design

Practice wiring and components

Questions last reviewed: 18 October 2026