What defines a balanced pair and why is it used in copper cabling?

• A. Two conductors carrying the same current direction
• B. Two conductors with equal impedance and opposite currents; reduces noise and improves common-mode rejection.
• C. A single conductor with no return path
• D. Two conductors separately grounded

Answer: (B)

A balanced pair is two conductors that carry signals with equal impedance and opposite polarity, forming a differential signal. The receiver looks at the voltage difference between the two wires, so any noise that induces the same voltage on both wires—the common-mode noise—is largely canceled when the signals are subtracted. The equal impedance keeps the pair symmetric, preserving signal integrity and minimizing reflections at high frequencies. In copper cabling, especially twisted-pair Ethernet, this arrangement reduces external interference, lowers emissions, and supports longer, higher‑speed runs because the system relies on differential signaling rather than a single-ended signal referenced to ground.