Red Seal Electrician Practice
Motor controlsQuestion 33 of 1506

What is an advantage of PLC logic over relay logic when one input is needed in several places?

  1. An input can only be used once in a program, which prevents logic errors
  2. Each input is a bit in memory, so it can be used as many times as needed
  3. Each extra use needs one more input terminal on the PLC input module
  4. Each extra use needs one more relay that has two normally open contacts
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Correct answer: Each input is a bit in memory, so it can be used as many times as needed

In a relay circuit each extra use needs another contact. In a PLC it is free.

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

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Questions last reviewed: 18 October 2026