Practice Test Geeks(E2) E2 Commercial Electrical Inspector Practice Test
← All E2 Flashcard Decks

Conductor Ampacity and Derating Flashcards

7 cards from real E2 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Conductor Ampacity and Derating flashcards as text

  1. Under NEC 310.15(C)(1), what adjustment factor applies when 4 to 6 current-carrying conductors are installed in the same raceway?

    Answer: 0.80

    NEC Table 310.15(C)(1) specifies a 0.80 (80%) adjustment factor when 4 to 6 current-carrying conductors occupy the same raceway or cable.

  2. A commercial building has a 3-phase 4-wire system with 15 current-carrying conductors in one large conduit. According to NEC Table 310.15(C)(1), what adjustment factor applies?

    Answer: 0.60

    For 10 to 20 current-carrying conductors in a raceway, NEC Table 310.15(C)(1) requires an adjustment factor of 0.50.

  3. What is the purpose of applying both a temperature correction factor AND a bundling adjustment factor to a conductor's ampacity?

    Answer: Both factors apply simultaneously because elevated ambient and bundling each independently raise conductor temperature

    Elevated ambient temperature and bundled conductors are independent heat sources that both limit a conductor's ability to dissipate heat, so both correction factors must be applied together by multiplication.

  4. NEC 310.15(B)(1) provides correction factors for ambient temperatures above or below the base temperature. What is the standard base temperature used for the 90°C column?

    Answer: 30°C

    The NEC ampacity tables are based on a 30°C ambient temperature as the reference; correction factors are applied when the actual ambient differs from 30°C.

  5. An inspector finds a raceway with 3 THHN phase conductors plus 1 THHN neutral that carries significant harmonic current from nonlinear loads. How many current-carrying conductors are counted for bundling?

    Answer: 4 — all four conductors are counted

    Per NEC 310.15(E)(2), a neutral on a system with nonlinear loads that generates significant harmonic current must be counted as a current-carrying conductor, making the total 4.

  6. In a commercial high-rise, cables are installed in a cable tray in a ventilated space. Which ampacity table from NEC Article 310 would apply to single conductors installed in cable tray without a maintained spacing?

    Answer: NEC 392.80(A) — cable tray provisions govern

    NEC 392.80 governs ampacity for conductors and cables in cable trays; single conductors in cable tray without maintained spacing use the cable tray provisions, not Table 310.16 or 310.17.

  7. A 2 AWG copper THHN conductor serves a 225A panelboard feeder with all continuous loads. What minimum ampacity is required before applying any derating?

    Answer: 281A

    For 100% continuous loads, NEC 215.2 requires the conductor ampacity to be at least 125% of the load: 225A × 1.25 = 281.25A, so 281A minimum is required before applying any derating factors.