One cable, three jobs
A single twisted pair cable can carry a phone call, a web page and enough power to run a small camera.
That is why copper is still in almost every office. But it has limits. This lesson goes beyond the four kinds you met in the core course and shows why and where each copper cable is used.
Key words
| Word | What it means |
|---|---|
| Twisted pair | two copper wires twisted together to cut noise |
| UTP | unshielded twisted pair: no metal screen |
| STP | shielded or screened twisted pair: a metal screen round the pairs |
| FTP | foil twisted pair: a thin foil wrap round the pairs |
| Coaxial | a cable with a copper core, a plastic layer and a braid screen |
| PoE | power over Ethernet: power sent down the data cable |
| Bandwidth | how much data a link can carry each second |
| Telephony | voice calls over a cable |
| Permanent link | the fixed cable from the patch panel to the wall outlet |
| Channel | the whole path from one device to the other, with every patch cord |
| Ethernet | the common way to join wired devices in an office |
| EMI | electromagnetic interference: a disturbance from nearby electrical kit |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can give the features and uses of copper cable, state the 90 m and 100 m limits, and describe each copper cable type.
Starter: cable kinds
Have a go
Starter: cable kinds
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Why use copper
Copper is durable: it takes knocks. It is easy to handle: it bends, and ordinary tools terminate it. It is cheaper to install than fibre, because cable, plugs and tools cost less. It has high bandwidth for the length of a floor.
It can also carry power, called PoE, so a phone, camera or wireless point needs only one cable.
Where copper is used
Copper serves telephony distribution inside a building. It serves short runs of Ethernet: the permanent link is at most 90 metres, and the whole channel at most 100 metres.
Beyond that, the signal is too weak, so you move to fibre or add a switch part way.
Copper cable types
| Type | What it is | Noise and EMI | Typical use |
|---|---|---|---|
| Twisted pair (TP) | Pairs of wires twisted together | The twist cuts electrical noise | Telephone circuits |
| UTP | No shield | Twist reduces noise and EMI | Normal office data runs |
| STP (screened) | A metal screen, earthed | Screen blocks EMI | Noisy places |
| FTP (foil) | A foil wrap round the pairs | Foil blocks much EMI | Mixed offices with some noise |
| Coaxial | Copper core, plastic layer, braid, outer jacket | Braid blocks EMI | TV, older CCTV and some radio links |
The cells students fill in are left blank in this preview.
How shielding is named
A cable name often has two letters round a slash. The letters before the slash tell the screen over the whole cable. The letters after tell the screen on each pair.
U means none, F means foil, S means braid. So U/UTP has no screen. F/UTP has foil over the whole cable. S/FTP has braid over the cable and foil on each pair.