Cabling & Connectors
Signals are only as good as the cable carrying them. This guide covers the wire and cable a technician works with daily — conductor sizing, coaxial cable and its impedance, twisted-pair categories, the common connectors, and the rules for choosing and installing cable safely.
Wire size is given by the American Wire Gauge (AWG) number, and the counterintuitive rule is that a smaller gauge number means a larger diameter.iAWG runs backwards: #8 wire is much thicker than #20. Each 3-gauge step roughly doubles (or halves) the cross-sectional area. Bigger conductor = more current capacity, less resistance. A #8 wire is far thicker than #20. A larger conductor carries more current with less voltage drop. The properties that matter for a conductor are its diameter/area, resistance, current capacity, and insulation rating — notably not its capacitance, which is a cable property, not a single-conductor spec.
Coax carries a signal on a center conductor surrounded by a dielectric, a shield (braid/foil), and a jacket. The shield confines the field and rejects interference, which is why coax is used for RF and video. Its defining spec is characteristic impedance — a value (commonly 50 Ω for radio/RF and 75 Ω for video/CATV) set by the cable's geometry, not something you measure with an ohmmeter.
Two more rules the exam likes: loss rises with frequency — the same coax attenuates a 1 GHz signal far more than a 100 MHz one — and you must match impedances. Connecting cables or loads of different impedance causes reflections and standing waves, wasting power and potentially damaging equipment.
Twisted-pair cable twists each signal pair to cancel interference, and comes in performance categories for data networking. Higher category = higher bandwidth and data rate:
| Category | Typical use |
|---|---|
| Cat 5e | Gigabit Ethernet (1 Gbps) to ~100 m. The old workhorse. |
| Cat 6 | 1 Gbps easily; 10 Gbps over shorter runs. Common today. |
| Cat 6a | 10 Gbps to 100 m. Better shielding against crosstalk. |
| Cat 7 / 8 | Higher-frequency, heavily shielded; data-center and specialty runs. |
STP vs. UTP: shielded twisted pair (STP) adds a foil/braid shield for noisy environments; unshielded (UTP) is cheaper and most common. Twisted pair terminates in the familiar RJ-45 8-pin connector for Ethernet.
Choosing cable isn't just about the conductor — the jacket rating matters for where it can be installed. Cable run in a building's air-handling spaces (plenums) must use fire- and smoke-rated jacketing so it doesn't release toxic smoke in a fire.