Practice Test GeeksIEC - Independent Electrical Contractors Practice Test
← All IEC Flashcard Decks

Overcurrent Protection Flashcards

6 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 6 Overcurrent Protection flashcards as text

  1. According to NEC® 240.21, where must an overcurrent protective device (OCPD) be located in a circuit?

    Answer: At the point where the conductor to be protected receives its supply.

    NEC® 240.21 generally requires that overcurrent protection be provided in each ungrounded conductor at the point where the conductors receive their supply, with some specific exceptions for taps and transformer secondaries.

  2. A feeder is protected by a 300A circuit breaker. Under the '25-foot tap rule,' what is the minimum required ampacity of a tap conductor connected to this feeder?

    Answer: 100A

    The '25-foot tap rule' in NEC® 240.21(B)(2) requires that the ampacity of the tap conductors be not less than one-third (1/3) of the rating of the overcurrent device protecting the feeder conductors. Therefore, 300A / 3 = 100A.

  3. Which of the following is NOT a standard ampere rating for a fuse or inverse time circuit breaker according to NEC® 240.6(A)?

    Answer: 120A

    NEC® Table 240.6(A) lists the standard ampere ratings for fuses and fixed-trip circuit breakers. The standard sizes include 90A, 110A, and 150A, but 120A is not listed as a standard size.

  4. In a motor branch circuit, the short-circuit and ground-fault protective device is sized larger than the conductor's ampacity. What is the primary reason for this allowance?

    Answer: To allow for the high inrush current when the motor starts.

    NEC® Article 430 allows the branch-circuit short-circuit and ground-fault protective device to be sized higher than the conductor's ampacity to prevent tripping during the motor's starting period, which involves a high inrush current. Overload protection is a separate device.

  5. An electrician is installing a new branch circuit for a continuous load of 18A using THHN copper conductors. What is the minimum required rating for the overcurrent protection device?

    Answer: 25A

    For continuous loads, the overcurrent device must be sized to be no less than 125% of the load. 18A * 1.25 = 22.5A. Since 22.5A is not a standard OCPD size, the 'next size up' rule from NEC® 240.4(B) permits using the next standard size, which is 25A.

  6. Which of the following BEST describes the function of 'supplementary overcurrent protection' as defined by the NEC®?

    Answer: It is used in addition to a branch-circuit OCPD for specific equipment protection.

    Supplementary overcurrent protection, as described in NEC® 240.10, is used for luminaires, appliances, and other equipment to provide additional protection beyond the main branch-circuit OCPD. It is not a substitute for branch-circuit protection and is not required to be readily accessible.