Red Seal Electrician Practice
Motor controlsQuestion 25 of 1506

What was the original purpose of a programmable logic controller (PLC)?

  1. To replace the power transformers in motor control centres with a small computer
  2. To measure the current in three-phase feeders by using stored-program logic
  3. To replace electromechanical relays as logic elements
  4. To provide emergency lighting during outages by using solid-state devices
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Correct answer: To replace electromechanical relays as logic elements

A PLC copies the interconnection of many relays in software.

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

Practice motor controls

Questions last reviewed: 18 October 2026