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Branch Circuit Calculations Flashcards

7 cards from real Licensed Electrical Contractor 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. A 240V branch circuit is protected by a 50-ampere breaker and supplies an electric range. What is the maximum continuous load in amperes?

    Answer: 40 amperes

    Continuous loads are limited to 80% of the overcurrent device rating: 50A × 0.80 = 40 amperes.

  2. Per NEC 210.19(A), what must the ampacity of branch circuit conductors be for a continuous load plus noncontinuous load?

    Answer: 125% of continuous load plus 100% of noncontinuous load

    NEC 210.19(A)(1) requires conductor ampacity of not less than 125% of continuous load plus 100% of noncontinuous load.

  3. A branch circuit serving a 1.5 HP, 120V single-phase motor must have conductors rated at a minimum of what percentage of the motor's full-load current?

    Answer: 125%

    NEC 430.22 requires branch circuit conductors for a single motor to be rated at not less than 125% of the motor's full-load current.

  4. What is the calculated load for a 12,000 VA central electric heating unit on a branch circuit, after applying the 100% demand factor required by NEC 220.51?

    Answer: 12,000 VA

    NEC 220.51 requires fixed electric space heating loads to be calculated at 100% of their total connected load, so 12,000 VA.

  5. A branch circuit conductor run of 150 feet uses 12 AWG copper wire at 20A on a 120V circuit. If the resistance of 12 AWG is 1.98 ohms per 1,000 feet, what is the approximate voltage drop?

    Answer: 11.88 volts

    VD = 2 × (1.98/1000) × 150 × 20 = 2 × 0.297 × 20 = 11.88V (round-trip conductor length doubled).

  6. For a multioutlet assembly used in a commercial setting where appliances are likely to be used simultaneously, the NEC requires a load of how many VA per linear foot?

    Answer: 180 VA per foot

    NEC 220.14(H)(2) requires 180 VA per linear foot when appliances are likely to be used simultaneously on multioutlet assemblies.

  7. A branch circuit has both a 4,000 VA continuous load and a 2,000 VA noncontinuous load. What minimum conductor ampacity is required at 240V?

    Answer: 29.2 amperes

    Required ampacity = (4,000 × 1.25 + 2,000) / 240 = (5,000 + 2,000) / 240 = 7,000 / 240 ≈ 29.2 amperes.