It looks fine, so is it?
You make a cable. Every colour is in the right place. You plug it in and the link light comes on.
But the link drops every ten minutes. One wire is loose inside the plug.
You cannot see this by looking. A test finds it in seconds.
Key words
| Word | What it means |
|---|---|
| Wire map | a test that shows which pin at one end joins to which pin at the other |
| Continuity | an unbroken path for the signal along a wire |
| Open | a wire that is broken, so the signal cannot pass |
| Short | two wires touching each other by mistake |
| Reversed pair | the two wires of one pair swapped at one end |
| Split pair | two wires from different pairs used as if they were a pair |
| Cable tester | a small tool with a light for each wire at both ends |
| Standard | an agreed set of rules that everyone follows |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can say what a cable test checks and read a tester result.
Starter
Have a go
Starter
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
What a test checks
A cable must meet the standard, which is TIA/EIA-568 for wiring. A test checks:
Wire map: does each pin join to the right pin at the other end?
Continuity: does the signal pass along every wire?
Length: is it within the limit of 100 metres in all?
The faults a test finds
| Fault | What is wrong | What the lights show |
|---|---|---|
| Open | A wire is broken or not pushed in | One light never comes on |
| Short | Two wires touch | Two lights come on together |
| Reversed pair | Both wires of a pair swapped at one end | Two lights come on in swapped order |
| Crossed | Wires in the wrong places | Lights come on in the wrong order |
| Split pair | Wires from two different pairs are joined | The lights look right, but the cable fails a full test |
The cells students fill in are left blank in this preview.
Quick check
Have a go
Quick check
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.