Red Seal Electrician Practice
Motor controlsQuestion 37 of 1506

What are internal coils and contacts in a PLC program used for?

  1. Switching the 120 V AC supply directly to the field devices on the machine itself
  2. Measuring the input voltage on a terminal and showing it on a display
  3. Logic and inversion, like control relays, with no outside link
  4. Supplying power to the front-panel LEDs that show the input status
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Correct answer: Logic and inversion, like control relays, with no outside link

They act like control relays CR1, CR2 and so on.

Source: Lessons in Electric Circuits IV: Digital (Kuphaldt), 6.6: Programmable Logic Controllers (PLC)

Practice motor controls

Questions last reviewed: 18 October 2026