What to check immediately after installation
Before connecting the tester, inspect the line. Check the integrity of the cable sheath along the entire accessible length: absence of kinks, creases and signs of mechanical impact. At points where the cable passes through walls and floors, make sure the cable is not chafed or pinched. Inspect the connectors and outlet modules: all eight wires must reach the front wall of the connector, the sheath must be secured by the strain relief, and on the outlet — terminated according to the chosen T568A or T568B scheme. If you laid the line in corrugated conduit or cable duct, check that the bending radius is not less than the permissible value: details are described in the material about UTP cable installation.
Checking with a simple LAN tester
A simple LAN tester (verifier) consists of a main and a remote unit connected by the cable under test. It checks the integrity of each wire and their connection order — wiremap. The indicators on both units should light up alternately for contacts 1–8. If the order matches, the cable is crimped correctly. Such a tester detects opens, shorts, crossed pairs and reversed pairs. Some models additionally detect split pairs if the line length exceeds 0.6 m. The verifier does not measure attenuation, crosstalk and return loss, so it does not confirm that the line complies with Cat5e or Cat6.
To locate an open and determine the distance to the fault, testers with a TDR (Time Domain Reflectometry) function are used. They send a short pulse into the line and measure the return time of the reflection. The cable length and distance to the defect are calculated from the time. The accuracy of TDR testers depends on the model and is usually specified in the manufacturer’s documentation.
Typical faults and their symptoms
Open. One or more wires do not conduct signal. Causes: wire did not reach the contact in the connector, poor crimp, cable break during installation. The tester shows no connection on the corresponding contact. Use TDR mode to locate the open.
Short. Two wires contact each other. Causes: burr on the connector, insulation damage, conductive material between contacts. The tester shows a connection between contacts that should be isolated.
Reversed Pair / Crossed Pair. Wires are connected to the wrong contacts on one or both ends. Cause: incorrect wire arrangement during crimping or outlet termination. Crossed Pair also occurs when mixing T568A and T568B schemes on the ends of one line. The tester shows an incorrect order of indicator lighting.
Split Pair. The most complex defect. One wire from one pair and one wire from another pair are used as a pair for data transmission. This disrupts matching and leads to a sharp increase in crosstalk. Cause: incorrect termination of the outlet or patch panel. Split pair may not be detected by a simple tester if it does not support this function. The minimum line length for detecting split pair is 0.6 m.
Table of tester results and causes
| Tester result | Possible cause | What to check |
| Indicator does not light | Open wire | Check contact in connector and outlet, test the cable |
| Indicators light in wrong order | Crossed pairs | Check arrangement according to T568A or T568B on both ends |
| Two indicators light simultaneously | Short circuit | Inspect connector for burrs and insulation damage |
| Indicator of one wire in a pair does not light | Open or poor contact | Check connector crimp, test the wire |
| Tester shows no error but network does not work | Split pair or high losses | Check outlet termination, use a certification tester |
| Line length in TDR mode shorter than actual | Open or cable damage | Inspect cable for damage, check contacts |
Checking the quality of Cat5e and Cat6
A successful wiremap test confirms only correct connection, but does not guarantee category compliance. To check the quality of the line, a certification analyser is used. It measures parameters at high frequencies: Insertion Loss, Return Loss, Near-End Crosstalk (NEXT), Power Sum NEXT (PSNEXT), Attenuation-to-Crosstalk Ratio (ACR-N, ACR-F) and others. The results are compared with the limits established by ANSI/TIA-568.2-D and ISO/IEC 11801-1. The certification tester must comply with ANSI/TIA-1152 requirements for measurement accuracy. Only such a device gives a reliable assessment of the line’s compliance with the category.
For Cat5e, tests are performed in the range up to 100 MHz, for Cat6 — up to 250 MHz. If the line works at 100 Mbit/s instead of 1 Gbit/s, the likely cause is split pair, cable damage during installation or a poor-quality connector. A simple tester does not detect such defects. Diagnostics requires a certification analyser or a qualification tester that assesses whether the line supports the required speed.
Troubleshooting algorithm
- Visual inspection. Check connectors, outlets and cable integrity.
- Wiremap test. Connect a LAN tester and check the wire order. If the order is wrong, re-crimp the connector.
- Locating an open. If the tester shows an open, use TDR mode to determine the distance to the fault. Compare with the actual route length.
- Checking for split pair. If wiremap is correct but the line does not work at 1 Gbit/s, check the outlet and patch panel termination for split pair.
- Certification. To confirm compliance with Cat5e or Cat6, call a specialist with a certification analyser. They will measure all parameters and issue a report.
Typical mistakes
Considering a simple tester sufficient to confirm the category. The verifier checks only integrity and wire order. It does not measure attenuation and crosstalk. The line may pass a wiremap test but not comply with Cat5e or Cat6.
Ignoring split pair. The defect is not always detected by a simple tester, but sharply reduces throughput. If the line works unstable or only at 100 Mbit/s, check the outlet termination.
Using an incorrect NVP when measuring length. The TDR tester calculates length based on the nominal velocity of propagation (NVP), which is specified in the cable documentation. If an incorrect value is entered into the tester, the length measurement will be wrong.
Not testing the line after reworking the connector. After re-crimping, be sure to repeat the wiremap test. The connector blades may not have cut through the insulation or may have damaged the wires.
FAQ
How does a simple LAN tester differ from a certification analyser?
A simple LAN tester (verifier) checks wire integrity and connection order. A certification analyser measures high-frequency parameters: attenuation, crosstalk, return loss — and compares them with the standard limits. Only a certifier confirms that the line complies with Cat5e or Cat6.
How to find the location of a cable break?
Use a tester with a TDR function. It sends a pulse into the line and calculates the distance to the fault from the return time of the reflection. Compare the resulting distance with the actual route length.
Why does the line work only at 100 Mbit/s instead of 1 Gbit/s?
Probable causes: split pair, cable damage during installation, poor-quality connector or exceeded line length. A simple tester does not detect such defects. A certification analyser or qualification tester is required.
What is split pair and how to detect it?
Split pair is the use of one wire from one pair and one wire from another pair as a pair for data transmission. This disrupts matching and increases crosstalk. It is detected by a tester that supports the split pair function when the line length is more than 0.6 m.
Can a regular multimeter be used to test a UTP cable?
A multimeter checks only wire integrity and the presence of a short circuit. It does not check connection order and does not detect split pair. To test a UTP line, use a LAN tester or a certification analyser.
Sources
- ANSI/TIA-568.2-D «Balanced Twisted-Pair Telecommunications Cabling and Components Standard» — in force — TIA TR-42 committee — certification parameters, limits for Cat5e and Cat6, maximum permanent link length 90 m.
- ANSI/TIA-1152-A «Requirements for Field Test Instruments and Measurements for Balanced Twisted-Pair Cabling» — in force — requirements for field tester accuracy, accuracy levels Level II, III, 2G.
- ISO/IEC 11801-1:2017 «Information technology — Generic cabling for customer premises — Part 1: General requirements» — in force — cabling line parameters, classes D, E, EA, F, FA.
- IEC 61935-1:2019 «Specification for the testing of balanced and coaxial information technology cabling — Part 1: Installed balanced cabling as specified in ISO/IEC 11801-1» — in force — measurement procedures, field tester accuracy requirements.
- Fluke Networks. «What’s Wrong with My Cable?» — technical article — flukenetworks.com — causes of wiremap faults: Open, Short, Reversed Pair, Crossed Pair, Split Pair; causes of Return Loss and Insertion Loss failures.
- Fluke Networks. «MicroMapper Wiremap Tester» — technical documentation — flukenetworks.com — detection of opens, shorts, reversed and split pairs, minimum length for split pair detection 0.6 m.
- Fluke Networks. «DSX CableAnalyser Series Copper Cable Certifiers» — technical documentation — flukenetworks.com — certification parameters: Wire Map, Length, Propagation Delay, Insertion Loss, Return Loss, NEXT, PSNEXT, ACR-N, ACR-F, PSACRF.
- Leviton. «Application Note: Three Cabling Subsystems» — technical guide — leviton.com — permanent link 90 m, channel 100 m, total patch cord length 10 m.
- UNI-T. «UT685A KIT TDR Cable Tester» — technical documentation — meters.uni-trend.com — TDR length measurement, accuracy, range 2.5–300 m.
- KazKabel. «UTP cable installation: installation norms inside, outside, in the ground and on a messenger wire» — practical guide — kazkabel.kz — laying rules, installation temperature, UV resistance.
