Red Seal Electrician Practice
Motor controlsQuestion 105 of 1506

Two normally closed contacts are in parallel with a lamp. When does the lamp go out?

  1. Only when both contacts are actuated at the same time
  2. When either contact is actuated, since a path to the lamp then opens
  3. When neither contact is actuated, since both paths are then closed
  4. Never, because the lamp stays on in all of the switch states
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Correct answer: Only when both contacts are actuated at the same time

This is the NAND function. The lamp is on when either contact is unactuated.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 6.2: Digital Logic Functions

Practice motor controls

Questions last reviewed: 18 October 2026