Telecom Room Cross-Connection Facility Practice Test

The main idea is the characteristic impedance of copper twisted-pair used for backbone cabling. For 24–22 AWG copper conductors in this type of backbone, the standard design target is a nominal impedance of 100 ohms, which is what balanced twisted-pair Ethernet cabling (like Cat5e/Cat6) is specified to have. This impedance is determined by the geometry of the pair—the twist rate, conductor spacing, and insulation—not by the DC resistance of the wires, so the AWG size mainly affects resistance and attenuation rather than changing the intended impedance. Other impedance values (50, 75, 120 ohms) are common in different media—coaxial RF, video/coax, or certain balanced lines—but they do not apply to typical copper backbone twisted-pair Ethernet.