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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 120V single-phase circuit runs 250 ft (one-way) using 12 AWG copper (1.98Ω/1000 ft). What is the round-trip voltage drop at 15A?

    Answer: 14.85V

    VD = 2 × 250 × (1.98/1000) × 15 = 14.85V.

  2. A power factor correction capacitor bank is added to a facility. The primary benefit is:

    Answer: Reducing reactive power demand and improving power factor

    Capacitor banks supply reactive power locally, reducing reactive current from the utility and improving power factor.

  3. What is the RMS voltage of a sine wave with a peak voltage of 170V?

    Answer: 120V

    V_rms = V_peak / √2 = 170 / 1.414 ≈ 120V.

  4. A delta-connected transformer secondary has a phase voltage of 240V. What is the line voltage?

    Answer: 240V

    In a delta connection, line voltage equals phase voltage: V_line = V_phase = 240V.

  5. The time constant (τ) of an RC series circuit determines:

    Answer: The rate at which the capacitor charges or discharges

    τ = R × C; after one time constant the capacitor reaches about 63.2% of supply voltage.

  6. In a balanced 3-phase wye (Y) system, the line current equals:

    Answer: The phase current

    In a wye connection each line conductor carries only one phase winding's current, so I_line = I_phase.

  7. A 10kW continuous resistive load on 240V single-phase requires a circuit breaker sized at 125%. What is the minimum standard breaker size?

    Answer: 60A

    I = 10,000/240 = 41.67A; × 1.25 = 52.08A; the next standard breaker size above 52A is 60A.