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Service and Load Calculations Flashcards

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  1. What is the maximum unbalanced load used to size the neutral conductor for a 120/240V single-phase service with a 100-ampere load on each hot leg and 80 amperes on the neutral?

    Answer: 80 amperes

    The neutral conductor must be sized for the maximum unbalanced load, which is 80 amperes in this scenario.

  2. Per NEC 220.61, a demand factor of 70% may be applied to the neutral load for which type of load above 200 amperes?

    Answer: Electric cooking equipment and dryers

    NEC 220.61(B)(1) allows a 70% demand factor on the neutral load for household ranges, wall-mounted ovens, counter-mounted cooking units, and clothes dryers above 200 amperes.

  3. A motor with a full-load current of 28 amperes is the largest motor in a panel. Per NEC 220.50, what additional load is added for motor calculations?

    Answer: 25% of 28 A = 7 A

    NEC 220.50 refers to Article 430, which requires adding 25% of the largest motor's FLA to the total load for feeder and service sizing.

  4. When sizing the service for a commercial occupancy with 50,000 VA of connected lighting, what demand factor applies to the first 20,000 VA per NEC Table 220.42?

    Answer: 100%

    NEC Table 220.42 applies 100% to the first 20,000 VA of lighting load for commercial occupancies.

  5. A residential air conditioning unit draws 24 amperes at 240 volts and the electric heat load is 10 kW. Which load is omitted from the service calculation per NEC 220.60?

    Answer: The smaller of the two loads is omitted

    NEC 220.60 permits omitting the smaller of the non-coincident heating or cooling loads since both are unlikely to operate simultaneously.

  6. For service entrance conductors, NEC 230.42 requires that the conductor ampacity must not be less than what percentage of the calculated load?

    Answer: 100%

    NEC 230.42(A) requires service entrance conductors to have an ampacity not less than the calculated load (100%).

  7. A 400-ampere service has a calculated load of 320 amperes. The neutral calculated load is 210 amperes. What is the neutral ampacity after applying the NEC 220.61 reduction?

    Answer: 200 amperes + 7 amperes = 207 amperes

    200 A at 100% = 200 A; (210 A − 200 A) × 70% = 7 A; total neutral = 207 amperes per NEC 220.61.