THE FAULT REFERENCE
Read the wiring.
Understand the failure.
Seven fault types. Clear connections, observable symptoms and honest test limits. These are explanatory schematics, not measured samples.
Compare T568A / T568B assignments ↓FAULT / 01
Open conductor
An interrupted conductor breaks one electrical path. The drawing opens pin 3; the other pins remain connected. A wiremap may show the affected pin, while a suitable distance function can provide an estimate from the test end. Neither result alone identifies an accessible repair point in the building.
- Possible observation
- Missing path on one conductor; a link may fail or negotiate differently, depending on the affected pairs and equipment.
- Basic tester boundary
- Usually found by continuity or wiremap when the fault is present.
- Next confirmation
- Verify both terminations and, where supported, compare distance readings from each end.
- What this does not prove
- An estimated electrical distance is not a marked position on a wall.
FAULT / 02
Short circuit
A short joins conductors that should remain electrically separate. This example bridges pins 1 and 2 while retaining the other paths. A suitable verifier can report the affected conductors, but the display and minimum detectable distance depend on the model. Disconnect active equipment before a passive wiring test.
- Possible observation
- A reported short, loss of link or a supply protection event; behaviour depends on the equipment.
- Basic tester boundary
- Usually found by a verifier that explicitly detects shorts.
- Next confirmation
- Inspect plugs, outlets, stray strands and damaged cable; retest after isolating each section.
- What this does not prove
- A short indication does not identify which connector or cable section caused it.
FAULT / 03
Reversed pair
A reversed pair swaps the two conductors within one pair at one termination. Here, pins 1 and 2 exchange positions; the pair membership is retained. This creates a pin-mapping error, which is different from a split pair. Verify the required termination scheme even if connected equipment appears to work.
- Possible observation
- Pins 1 and 2 appear exchanged in the remote map.
- Basic tester boundary
- A tester that displays the full pin map can identify the reversal.
- Next confirmation
- Compare both terminations with the specified T568A or T568B pin assignment.
- What this does not prove
- A working link does not demonstrate that the required wiring scheme was followed.
FAULT / 04
Crossed pairs
Crossed pairs exchange complete signal pairs between the two ends. This schematic exchanges the 1–2 pair with the 3–6 pair while leaving the other pairs unchanged. Some equipment can accommodate a crossover, but that behaviour does not change the wiring required by the installation specification or its acceptance test.
- Possible observation
- Two complete pairs map to different pin positions at the far end.
- Basic tester boundary
- A full pin map can show the crossover.
- Next confirmation
- Check the intended cable type, termination scheme and project requirement.
- What this does not prove
- Automatic crossover support is not evidence of cabling certification.
FAULT / 05
Split pair
A split pair can retain one-to-one pin continuity while assigning conductors from different physical twisted pairs to a signal pair. Here, the conductors at pins 4 and 6 are exchanged at both ends. A basic DC continuity test can therefore pass, although the required 3–6 and 4–5 pair membership is wrong.
- Possible observation
- Continuity can pass while interference or application performance is poor.
- Basic tester boundary
- A basic DC sequencer may miss it; explicit split-pair detection is required.
- Next confirmation
- Compare conductor colours and physical pair membership with the required pinout; use a suitable tester.
- What this does not prove
- An unusual length reading alone is not a reliable split-pair diagnosis.
FAULT / 06
Shield discontinuity
A shield discontinuity interrupts the screening connection while the eight signal conductors may remain correctly connected. This schematic shows a break in the shield path only. A tester with shield-continuity capability can check that electrical connection; it does not assess the complete installed bonding arrangement or prove successful tracing through the screen.
- Possible observation
- The signal wiremap can pass while a supported shield test reports an open.
- Basic tester boundary
- Only if the instrument and adapters provide an explicit shield test.
- Next confirmation
- Check screened connectors and terminations against the installation design.
- What this does not prove
- Shield continuity does not certify bonding quality, interference performance or tracing reliability.
FAULT / 07
Intermittent contact
An intermittent contact changes between connected and faulty states. The highlighted point represents that changing condition, not a fixed open or a measured result. A short test can pass if the contact is sound at that moment. Record the original trigger and use repeat observations to check whether a repair addresses it.
- Possible observation
- A link or powered device may drop only during certain operating or environmental conditions.
- Basic tester boundary
- May be missed when the contact is conducting during the check.
- Next confirmation
- Record the trigger and repeat the test during an agreed maintenance window; substitute suspect leads or terminations.
- What this does not prove
- One PASS cannot exclude a fault that was absent during the measurement.
Where do the eight conductors belong?
T568A and T568B exchange the orange and green pairs while retaining the blue and brown pair positions. Use the numbered assignments below alongside the connector manufacturer’s orientation marks. A plug contact view and a jack’s punch-down layout are different presentations; the pin numbers and physical pair membership are what you must verify.
Record the observation, then repeat the check.
Keep the sample identity, cable details, instrument model, mode and connection state with every result. A diagram can explain what a fault means, but it cannot establish what your own tester detected. Use the blank record to separate expected behaviour from observed readings, then repeat the original conditions after repair.
What evidence does this reference contain?
This reference contains original explanatory diagrams and published technical sources, not measurements of physical cable samples. Fault behaviour depends on the instrument and operating conditions. Use the diagrams to interpret a supported test, and consult the exact manual before making a live connection or treating a result as an acceptance test.