Red Seal Electrician Practice
Motor controlsQuestion 27 of 1506

What are the typical input and output signal levels of an industrial PLC, as described in the text?

  1. 120 V AC
  2. 600 V DC
  3. 5 V DC logic only
  4. 48 V three-phase
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Correct answer: 120 V AC

Like the relays they replace, PLC inputs and outputs are typically 120 V AC. Low-level DC is the exception.

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

Practice motor controls

Questions last reviewed: 18 October 2026