A data cable can look perfect and still not work properly. You cannot see a bad termination, a kinked cable or a crossed pair. The only way to know a link is right is to test it, and the test certificate is the proof.
What the tester actually does
A certification tester, such as the Fluke Networks DSX we use, connects to both ends of a link and checks it against the standard for that cable type. In plain English, it asks:
- Is every wire connected to the right place? (the wire map)
- How long is it? Copper links have a 100 metre limit.
- How much signal is lost along the way?
- Are the pairs interfering with each other? This is called crosstalk, and it is the most common reason a link fails.
- Is signal bouncing back? This is called return loss, and it usually points to a poor termination.
The result for each link is a simple pass or fail, with the measurements behind it.
Why every link, not a sample
Some installers test a few links and assume the rest are fine. We test every one. A link that is never tested is a fault waiting for your users to find it, usually at the worst possible moment. Most manufacturer warranties also expect a full set of test results before they will cover the system.
Why one failure costs so much
A skilled engineer terminates a keystone jack in under two minutes. Getting it right first time is quick. Putting it right later is not. When a link fails, someone has to:
- Find the fault from the test result.
- Open up a neatly dressed panel and loom, often disturbing the cables either side.
- Re-terminate the jack, or if the cable itself is damaged, pull a new one through finished containment.
- Re-dress the loom and retest the link.
- Update the records and the handover pack.
A two-minute job becomes an hour or more, and a run of failures can hold up a whole handover. That is why our aim on every comms room is simple: 100% pass, first time.
How we check: our own Fluke result reconciliation app compares every test result against the label schedule, so a missing or failed link is flagged straight away, not after we have left site.
What you should ask for
At handover, ask for the full test results for every link, in the tester's own report format, with the cable labels matching the drawings. If you cannot get them, you do not know what you have paid for.