Troubleshooting
Find the next useful test.
Start with a symptom, isolate one variable, and keep the result. A cable fault is one possibility—not the only one.
How do you narrow down a link fault?
Start by confirming the actual link rate and whether the problem affects one device, one outlet or several connections. Compare the same devices with a known-good short lead before replacing the installed cable. Change one variable at a time, and record the original symptom so you can repeat the check after repair.
- Record the link rate, affected devices and whether the link drops.
- Compare ports and patch leads one at a time with a known-good setup.
- Check the isolated cable with a suitable tester, then repeat the original test after repair.
- Fault findingAll eight lights pass. Why is Ethernet still at 100 Mb/s?
Separate a wiring fault from a 100 Mb/s port, a damaged pair or a configuration problem with a controlled Ethernet troubleshooting sequence.
7 min read - Measurement limitsCable length and distance-to-fault: what a tester can estimate
Understand electrical distance, NVP, reference points and far-end conditions before using a cable tester’s length or distance-to-fault reading.
6 min read
Which related test could help next?
Use the related guides to check another part of the diagnosis once the first comparison is complete. Wiring, application support and power delivery are different questions, so a result in one area may leave another unresolved. Select the next test from the remaining symptom, rather than treating every PASS as a complete answer.
- Tool selectionVerification, qualification or certification?
Understand what each level of network cable testing proves, which tool you need and what should appear in a cabling handover report.
6 min read - PoE & camerasPoE voltage is present. Why does the camera keep rebooting?
Check a PoE camera that restarts when infrared lighting or PTZ movement begins, using port budgets, known-good leads and loaded measurements.
7 min read
Which references support these checks?
The references below support the terminology, documented tool capabilities and external cases used in this category. Manufacturer information applies to the named instrument; a published case records another author’s observations. Follow the linked guide for the relevant scope and limitations, and use the project specification to determine any required acceptance test.
- Fluke Networks — split-pair identification
- Fluke Networks — cable verification, qualification and certification
- Gough’s Tech Zone — a gigabit link falling back to 100 Mb/s
- Fluke Networks — determining cable NVP on the DTX CableAnalyzer
- The FOA — illustrated wiremap faults
- HSE — avoiding danger from underground services (HSG47)