Practice Test Geeks(E2) E2 Commercial Electrical Inspector Practice Test
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Conductor Ampacity and Derating Flashcards

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  1. Under NEC 310.15(B)(3)(a), what allowance is made for conductors installed in a nipple of 24 inches or less?

    Answer: No derating for bundling is required for conductors in short nipples

    NEC 310.15(B)(3)(a) provides an exception that conductors in a nipple not exceeding 24 inches are not required to be derated for bundling.

  2. A 250 kcmil copper THHN conductor has a listed 90°C ampacity of 255A. The equipment termination is rated 75°C. What maximum ampacity can be used?

    Answer: 215A

    With 75°C terminations, the 75°C column from NEC Table 310.16 governs; 250 kcmil copper at 75°C is 215A.

  3. When conductors are installed in a cable tray per NEC Article 392, which section governs their ampacity rather than Table 310.16?

    Answer: NEC 392.80

    NEC 392.80 provides the ampacity requirements specifically for conductors and cables installed in cable trays, which differ from conduit installation methods.

  4. Which of the following conductors is NOT counted as current-carrying when determining bundling adjustments?

    Answer: An equipment grounding conductor

    Equipment grounding conductors (EGCs) do not carry load current under normal conditions and are never counted as current-carrying conductors for bundling purposes.

  5. A 600V rated 1/0 AWG THHN copper conductor has a 90°C ampacity of 170A. If installed with 4-6 current-carrying conductors and ambient is 45°C, what is the derated ampacity?

    Answer: 98.5A

    Derated ampacity = 170A × 0.87 (temp correction at 45°C/90°C) × 0.80 (4-6 conductor adjustment) ≈ 118.3A, closest answer is 119.0A.

  6. For a feeder supplying a commercial occupancy, NEC 215.2 requires the feeder conductor ampacity to be at least what percentage of the noncontinuous load plus what percentage of the continuous load?

    Answer: 100% noncontinuous + 125% continuous

    NEC 215.2(A)(1) requires feeder conductors to have ampacity of not less than 100% of the noncontinuous load plus 125% of the continuous load.

  7. An E2 inspector is reviewing a commercial installation where 6 AWG THHN conductors are in a conduit exposed to direct sunlight on a rooftop. What adder to ambient temperature is required per NEC 310.15(B)(2)?

    Answer: 17°C added to the ambient temperature

    NEC 310.15(B)(2) requires a 17°C temperature adder for raceways exposed to direct sunlight on or above rooftops when within 7/8 inch to 3½ inches above the roof.