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Electrical Calculations and Theory 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 Electrical Calculations and Theory flashcards as text

  1. A 240V single-phase circuit supplies a 4,800W resistive load. What is the current draw?

    Answer: 20A

    I = P / V = 4,800 / 240 = 20A.

  2. What is the total resistance of a 10Ω and 15Ω resistor connected in parallel?

    Answer: 6Ω

    1/R = 1/10 + 1/15 = 5/30, so R = 6Ω.

  3. A 3-phase, 480V motor draws 30A at 0.85 power factor. What is the true (real) power consumed?

    Answer: 21,168W

    P = √3 × V × I × PF = 1.732 × 480 × 30 × 0.85 ≈ 21,168W.

  4. What happens to total capacitance when two capacitors are wired in series?

    Answer: It is less than the smallest individual value

    Series capacitors combine via the reciprocal formula, always yielding a total less than the smallest capacitor.

  5. In AC circuits, the term 'impedance' refers to:

    Answer: The total opposition to current including resistance and reactance

    Impedance (Z) is the vector sum of resistance (R) and reactance (X) in an AC circuit.

  6. A single-phase transformer has a 480V primary and 120V secondary. If the secondary delivers 10A, what is the primary current (ignoring losses)?

    Answer: 2.5A

    I_primary = I_secondary × (V_secondary / V_primary) = 10 × (120/480) = 2.5A.

  7. Using NEC guidelines, what is the maximum recommended voltage drop for a feeder circuit?

    Answer: 3%

    NEC recommends no more than 3% voltage drop on feeders and 5% total for feeders plus branch circuits combined.