Red Seal Electrician Practice
Wiring and componentsQuestion 618 of 1506

An appliance has a metal case and a three-prong plug. The hot wire inside touches the case. What does the third prong do?

  1. It gives a fault path back to the source that trips the breaker.
  2. It raises the case voltage so the user feels only a mild tingle.
  3. It opens the neutral wire so the appliance simply stops working.
  4. It stores the fault current in the case until the fault is cleared by hand.
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Correct answer: It gives a fault path back to the source that trips the breaker.

The ground wire gives fault current an easy path back to the source. The overcurrent device trips and the case does not stay live.

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

Practice wiring and components

Questions last reviewed: 18 October 2026