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Overcurrent Protection 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.

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  1. Per NEC 240.60, cartridge fuses and fuseholders for 250V shall NOT be used on systems where the nominal voltage between any two conductors exceeds:

    Answer: 250V

    Cartridge fuses rated 250V are limited to circuits where the voltage between any two conductors does not exceed 250V.

  2. Which overcurrent device characteristic describes the ability to interrupt a fault current without damage to itself?

    Answer: Interrupting rating

    The interrupting rating specifies the maximum fault current an overcurrent device can safely clear without being destroyed.

  3. Per NEC 240.33, enclosures for overcurrent devices must be mounted in a:

    Answer: Vertical position as close as practical

    NEC 240.33 requires overcurrent device enclosures to be mounted vertically unless this is shown to be impracticable.

  4. A Type S fuse adapter is inserted into an Edison-base fuseholder to accept which type of fuse?

    Answer: Type S plug fuse

    Type S adapters accept only Type S fuses of the matching ampere rating, preventing installation of an oversized fuse.

  5. Per NEC 240.21(C), transformer secondary conductors are not required to have overcurrent protection at the secondary terminals if the primary overcurrent device rating does not exceed the value calculated using which multiplier for a 2-wire secondary?

    Answer: 167%

    For a 2-wire transformer secondary, the primary OCPD may be up to 167% of the primary FLC as a substitute for secondary protection per NEC 240.21(C)(1).

  6. Which NEC article specifically addresses overcurrent protection for motors?

    Answer: Article 430

    NEC Article 430 contains the requirements for motor overcurrent protection, separate from the general rules in Article 240.

  7. A circuit breaker with a slash rating such as '120/240V' indicates it is suitable for use on:

    Answer: A solidly grounded system where the voltage to ground does not exceed the lower of the two values

    A slash-rated breaker (e.g., 120/240V) is listed for use on solidly grounded systems where the line-to-ground voltage does not exceed the first number and line-to-line does not exceed the second.