📘 05-04: Cable Issues, Tools & PoE¶
🔌 Common Cabling Problems¶
| Problem | Symptom | Fix |
|---|---|---|
| Attenuation | Weak/failing signal on long runs | Stay within distance limits; use fiber |
| Crosstalk (NEXT/FEXT) | Errors, degraded throughput | Proper twists, quality terminations |
| EMI/RFI | Intermittent errors near noise | Use STP or fiber; reroute |
| Open / short / miswire | No link or wrong pairs | Re-terminate; verify with tester |
| Dirty/damaged fiber end | High insertion loss | Inspect and clean end-face |
| Bend radius exceeded | Fiber signal loss | Re-route respecting bend radius |
🧰 Diagnostic Tools¶
| Tool | Purpose |
|---|---|
| Cable tester / wiremap | Opens, shorts, miswires, pin mapping |
| Cable certifier | Certifies to category (crosstalk, attenuation) |
| Toner probe | Trace a specific cable in a bundle |
| OTDR | Locate fiber breaks/splices, measure loss |
| Light meter / power meter | Measure fiber insertion loss (dB) |
📌 Power over Ethernet (PoE)¶
PoE delivers DC power + data over the same twisted-pair cable — powering APs, IP phones, and cameras.
| Standard | Name | Power (source) |
|---|---|---|
| 802.3af | PoE | ~15.4 W |
| 802.3at | PoE+ | ~30 W |
| 802.3bt | PoE++ / 4PPoE | ~60–100 W |
📌 Cable Fire Ratings¶
| Rating | Where |
|---|---|
| Plenum (CMP) | HVAC air spaces — less toxic smoke |
| Riser (CMR) | Vertical shafts between floors |
Tip
Key idea — Diagnose copper with a wiremap/certifier and fiber with an OTDR/power meter. PoE (802.3af/at/bt) powers devices over Ethernet. Use plenum cable in air spaces.
See also: Copper Cabling, Racks, Patch Panels & Terminations
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