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AC Power Baluns

December 15th Fact-of-the-Day

AC power is distributed to North American residences using a three-line circuit consisting of two 'hot' lines and a grounded neutral line. There is 240 volts RMS between the two hot lines. There is 120 volts RMS between each hot line and the neutral. Each 120 volt branch circuit within a residence connects between the grounded neutral and one or the other of the two incoming hot lines. The branch transmission lines are balanced, but their power sources are unbalanced, because one side is grounded. Just as audio lines with unbalanced feeds crosstalk to each other, unbalanced power lines radiate 60 Hz hum and harmonics to nearby lines and equipment. Article 530 of the U.S. National Electrical Code now recognizes this problem by authorizing use of unbalanced-to-balanced power transformers (baluns) on 120 volt branch power lines in applications where a low-electrical-noise environment is critical. ©2004 Martek International All rights reserved.


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