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Overcurrent Protection Flashcards

6 cards from real TN LLE 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 240.4(B), when can the next standard size overcurrent device be used above the conductor ampacity?

    Answer: When the ampacity does not correspond to a standard device rating AND the circuit does not supply multioutlet receptacle branch circuits

    NEC 240.4(B) permits the next higher standard overcurrent device rating when the conductor ampacity doesn't match a standard size, provided the circuit isn't a multioutlet receptacle branch circuit.

  2. What are the standard ampere ratings for fuses and circuit breakers per NEC 240.6(A)?

    Answer: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200 (and continuing)

    NEC 240.6(A) lists the standard ampere ratings starting at 15 and including specific values up through 6,000 amperes.

  3. Per NEC 240.21(B), what is the maximum length for a feeder tap conductor that is at least 1/3 the ampacity of the feeder OCPD?

    Answer: 25 feet

    NEC 240.21(B)(2) permits tap conductors up to 25 feet in length if they have ampacity not less than 1/3 of the feeder OCPD rating and terminate in a single OCPD.

  4. What is the difference between an inverse-time circuit breaker and an instantaneous-trip circuit breaker?

    Answer: Inverse-time provides both overload and short-circuit protection; instantaneous-trip provides only short-circuit protection

    Inverse-time breakers have a time-delay element for overload protection plus instantaneous trip for short circuits. Instantaneous-trip breakers respond only to short-circuit level faults.

  5. Per NEC 240.24(A), what accessibility requirement applies to overcurrent devices?

    Answer: They must be readily accessible

    NEC 240.24(A) requires overcurrent devices to be readily accessible — meaning they can be reached without climbing, removing obstacles, or using portable tools.

  6. Per NEC 240.15, what requirement applies when a circuit breaker is used as a switch for normal load control?

    Answer: The breaker must be listed as suitable for switching duty (SWD or HID rated)

    NEC 240.15 requires circuit breakers used for switching 120V or 277V fluorescent lighting circuits to be listed and marked SWD or HID.