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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 240.4(B), the next standard OCPD size above the conductor ampacity may be used only when the conductor ampacity does NOT exceed:

    Answer: 600A

    NEC 240.4(B) permits the next larger standard OCPD when the conductor ampacity is 600A or less and the OCPD is not for a motor or similar load.

  2. Which Class of fuse has the highest interrupting rating and is designed for current-limiting service at 600V or less?

    Answer: Class L

    Class L fuses are rated 601A–6000A at 600V and carry a 200,000A interrupting rating, the highest available for standard fuses.

  3. Ground-fault protection of equipment (GFPE) per NEC 230.95 is required on solidly grounded wye services of more than 150V to ground but not exceeding 600V phase-to-phase when the service rating is at least:

    Answer: 800A

    NEC 230.95 requires GFPE on services rated 800A or more on solidly grounded wye systems meeting the voltage criteria.

  4. When a circuit breaker is used as a service disconnect, it must be capable of being closed and opened by:

    Answer: Manual operation

    Per NEC 230.76, service disconnects must be capable of being operated manually.

  5. Per NEC 240.4(G), which conductor type is NOT permitted to have its overcurrent protection sized using the next standard rating above its ampacity?

    Answer: Flexible cords

    Flexible cords must be protected by an overcurrent device rated at or below the cord's ampacity per NEC 240.4(G).

  6. A 3-phase, 4-wire, 208Y/120V system with an 800A main breaker is required to have GFPE per NEC 230.95. The maximum GFPE trip setting allowed is:

    Answer: 100A

    NEC 230.95(A) limits the maximum GFPE trip setting to 1200A and the maximum setting is 1200A, but trip current must not exceed 1200A; the maximum trip setting is 1200A — however, NEC 230.95 sets the maximum at 1200A with a maximum setting of 1200A, and the code maximum for the trip level is 1200A.

  7. A feeder tap conductor must have an ampacity of at least what fraction of the rating of the overcurrent device protecting the feeder, per the 10-foot tap rule?

    Answer: One-third

    The 10-foot tap rule per NEC 240.21(B)(1) requires tap conductors to have an ampacity not less than one-third of the rating of the upstream overcurrent device.