Operation Manual

Chapter 6
Structured cabling testing
61
6.7. Length Test
This test determines the length of wire pairs to ensure that the recommended limits for the
selected cable are complied with. Depending on the measurement unit selected in
"Preferences", the length is indicated in Foot or Meter.
Illustration 6.7. Length Test
6.7.1. Length Test Error
Minor length differences can occur between the wire pairs of a cable due to small NVP
differences, as well as length differences caused by transposition. A failure exists if the
electronically measured cable length deviates too much from the actual length.
6.8. Resistance Test
This test determines the loop resistance of the individual wire pairs. This ensures that the
total loop resistance does not exceed the recommended limits. For each wire pair, the results
are displayed as resistance value in ohm, together with the reference limit for the cable type.
Illustration 6.8. Resistance Test
6.8.1. Resistance Test Error
All four wire pairs of a transmission line within the network should have approximately the
same resistance. If the resistance value of a wire pair exceeds the limit, the test is considered
failed.
6.9. NEXT, ACR-F (ELFEXT) and Power Sum
In an Autotest, crosstalk at the near and far end of the cable is measured with NEXT (Near
End Cross Talk) and ACR-F (ELFEXT) tests. High crosstalk levels can result in frequent
recurrences, damage to data and other interferences that impair transmission rate.