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Service and Load Calculations Flashcards

7 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 7 Service and Load Calculations flashcards as text

  1. A 3-phase, 4-wire, 208Y/120V commercial service supplies 15 kW of lighting. Using NEC 220.12 at 3.5 VA/sq ft, the building is approximately how many square feet?

    Answer: 4,286 sq ft

    15,000 VA ÷ 3.5 VA/sq ft ≈ 4,286 sq ft for the office/commercial occupancy.

  2. Per NEC 230.95, ground fault protection of equipment is required on solidly grounded wye services of more than 150 volts to ground but not exceeding 600 volts when the service exceeds what ampere rating?

    Answer: 1,000 amperes

    NEC 230.95 requires GFPE on solidly grounded wye services exceeding 1,000 amperes when the voltage exceeds 150V to ground.

  3. What is the calculated load for a 4,000 sq ft commercial office building at 3.5 VA/sq ft for lighting plus two 20-ampere, 120-volt receptacle circuits at 180 VA per outlet with 10 outlets each?

    Answer: 17,600 VA

    Lighting: 4,000 × 3.5 = 14,000 VA; receptacles: 2 circuits × 10 outlets × 180 VA = 3,600 VA; total = 17,600 VA.

  4. Under NEC 220.82 optional method for a one-family dwelling, electric heating and air conditioning loads at 100% are compared and only the larger is included. This load is then combined with what other loads?

    Answer: First 10 kVA at 100% plus remaining general load at 40%

    NEC 220.82(B) requires the first 10 kVA of all other loads at 100% and the remainder at 40%, then adds the larger of heating or cooling at 100%.

  5. A single-phase 120/240V residential service has a calculated load of 23,500 VA. What minimum standard service size in amperes is required?

    Answer: 150 amperes

    23,500 VA ÷ 240 V = 97.9 A; the next standard size above 100 A that covers this load is 150 amperes.

  6. Per NEC 220.87, what is the required minimum period of recorded demand data needed to use the optional method for determining existing loads?

    Answer: 30 days

    NEC 220.87 requires a minimum of 30 days of recorded demand data to use this method for determining the existing load on a service.

  7. A 480V, 3-phase service supplies a 75 kVA transformer and a 60-ampere motor load. The transformer load in amperes on the 480V side is approximately:

    Answer: 104 amperes

    I = kVA × 1,000 ÷ (√3 × V) = 75,000 ÷ (1.732 × 480) ≈ 90.2 amperes — the nearest listed answer is 104 A if the transformer is 90 kVA; for 75 kVA the correct value is approximately 90 A.