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Motors and Motor Controls Flashcards

7 cards from real IEC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Motors and Motor Controls flashcards as text

  1. A motor nameplate shows a service factor of 1.15. What does this mean?

    Answer: The motor can operate continuously at 115% of its rated load

    A service factor of 1.15 means the motor can operate continuously at 115% of its nameplate horsepower without damaging insulation.

  2. Which type of motor starter uses reduced voltage to limit inrush current during starting?

    Answer: Autotransformer starter

    An autotransformer starter reduces starting voltage via a transformer, which significantly reduces inrush current during motor startup.

  3. What is the purpose of a motor's overload relay?

    Answer: To protect the motor from sustained overcurrent due to overloading

    Overload relays protect motors from sustained overcurrents caused by mechanical overloads, which generate excess heat and can damage windings.

  4. A three-phase motor is wired for wye (Y) connection. Compared to a delta connection, the phase voltage is:

    Answer: Lower than the line voltage by a factor of √3

    In a wye connection, phase voltage equals line voltage divided by √3 (approximately 0.577 × line voltage).

  5. Which NEC article primarily governs the installation of motors, motor circuits, and controllers?

    Answer: Article 430

    NEC Article 430 covers motors, motor circuits, and controllers including overcurrent protection and disconnecting means requirements.

  6. What type of enclosure is rated NEMA 4 and is suitable for outdoor use?

    Answer: Watertight and provides protection against rain, splashing, and hose-directed water

    NEMA 4 enclosures are watertight and dusttight, protecting against windblown dust, rain, sleet, and hose-directed water.

  7. When sizing branch circuit conductors for a single motor, the NEC requires the conductors to be rated at least:

    Answer: 125% of the motor's full-load current

    Per NEC 430.22, branch circuit conductors supplying a single motor must have an ampacity of at least 125% of the motor's full-load current rating.