Twisted Pair Copper Cables
Category ratings: Cat5e — 1 Gbps (1000BASE-T), 100m maximum segment. Cat6 — 1 Gbps up to 100m, 10 Gbps up to 55m. Cat6a — 10 Gbps up to 100m (augmented Cat6, thicker cable, better shielding). Cat7 / Cat8 — data center applications, shorter distances, stricter shielding. The '100-meter rule': maximum segment length for standard Ethernet over twisted pair is 100 meters (328 feet). Use fiber for longer runs.
UTP vs STP: UTP (Unshielded Twisted Pair) — standard for most office/home environments, flexible, easier to terminate. STP (Shielded Twisted Pair) — shielding on individual pairs or overall, used in high-EMI environments (near motors, industrial equipment). STP requires proper grounding to be effective; ungrounded shielding can worsen interference.
Connectors: RJ-45 — 8-pin connector used for Ethernet. RJ-11 — 6-pin (uses only 2-4 pins) used for telephone (POTS/DSL). RJ-45 and RJ-11 look similar — RJ-11 is narrower. Never force an RJ-11 into an RJ-45 port. Wiring standards: T568A and T568B — two standard wiring patterns for RJ-45 jacks. T568B is more common in the US. Use the same standard on both ends of a straight-through cable. Crossover cable uses T568A on one end and T568B on the other — connects like devices (PC to PC) directly. Modern switches support Auto-MDIX — automatically detect and correct crossover, making crossover cables largely unnecessary.
Fiber Optic and Coaxial Cables
Fiber optic: transmits data as light pulses — immune to EMI, can span much longer distances than copper. Single-mode fiber (SMF): thin 9-micron core, laser light source, yellow jacket — long distances (km). Multimode fiber (MMF): thicker 50/62.5-micron core, LED/VCSEL light source, orange or aqua jacket — shorter distances (up to ~550m for OM3/OM4). Fiber connectors: LC (most common in data centers, small form factor), SC (older enterprise), ST (older campus). Always inspect and clean fiber connectors — a dirty end-face degrades the signal dramatically.
Coaxial cable: center copper conductor surrounded by dielectric, braided shield, outer jacket. RG-6: broadband internet (cable modem), satellite, and cable TV. Connector: F-type (threaded). RG-58: older thin Ethernet (10BASE-2) — rarely seen today. BNC connector used with RG-58. Coax is more resistant to EMI than UTP and is used where cable TV/broadband cabling already exists.
Plenum vs riser vs non-plenum: plenum cable: low-smoke, fire-rated jacket — required in air-handling spaces (ceiling plenums, raised floors where HVAC air circulates). Burning plenum cable produces less toxic smoke. Riser cable: fire-rated for vertical runs between floors (must not spread flames between floors) — but cannot be used in plenum spaces. Non-plenum (PVC): standard cable — least expensive, not fire-rated for building runs. Always use plenum cable in HVAC spaces — building code requirement.