If a 120 volt circuit feeds six 80 watt fluorescent lamps, what current is drawn if power factor is 0.91?

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Prepare for the New York City Electrician Test. Study with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

Multiple Choice

If a 120 volt circuit feeds six 80 watt fluorescent lamps, what current is drawn if power factor is 0.91?

Explanation:
The current drawn comes from the apparent power, which combines real power with reactive power through the power factor. First find the real power the lamps use: 6 lamps × 80 W each = 480 W. With a power factor of 0.91, the apparent power is S = P / pf = 480 / 0.91 ≈ 527.5 VA. The current is then I = S / V = 527.5 VA / 120 V ≈ 4.40 A. So the circuit draws about 4.4 amps. Note that if the power factor were 1, the current would be 480/120 = 4.0 A, so a pf less than 1 increases the current slightly.

The current drawn comes from the apparent power, which combines real power with reactive power through the power factor. First find the real power the lamps use: 6 lamps × 80 W each = 480 W. With a power factor of 0.91, the apparent power is S = P / pf = 480 / 0.91 ≈ 527.5 VA. The current is then I = S / V = 527.5 VA / 120 V ≈ 4.40 A. So the circuit draws about 4.4 amps. Note that if the power factor were 1, the current would be 480/120 = 4.0 A, so a pf less than 1 increases the current slightly.

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