Balanced line
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In telecommunications, a balanced line is a transmission line consisting of two conductors in the presence of ground, which relies on balanced impedances to minimize interference. The signals on each line are typically the inverse of one another.
The conductors are carefully twisted together to ensure that each conductor is equally exposed to any external magnetic fields that would induce unwanted noise.
Capable of being operated in such a way that when the impedances of the two conductors at all transverse planes are equal in magnitude and opposite in polarity with respect to ground, the currents in the two conductors are equal in magnitude and opposite in direction.
Balanced lines can carry electrical signals farther than unbalanced lines because any noise on the line will not be balanced and thus gets filtered out.
For this reason, balanced lines sometimes do not have electrical shielding on the wires. For example UTP category 5 cable carries balanced signals.
To convert a signal from balanced to unbalanced requires a balun. For example, you can use baluns to send line level audio (which is unbalanced) over 300 feet of CAT5 cable by using a pair of baluns at each end of the CAT5 run.
Note: A balanced line may be operated in an unbalanced condition. Synonym balanced signal pair.