Why not one cable for everything?
A school has cables in the classrooms, between buildings and under the road. A cable between two buildings must be long. A cable next to a lift motor must ignore noise.
One cable cannot be best at both jobs. So there are four main kinds.
By the end of this lesson
Note
I can choose the right cable type for a job and give a reason.
Key words
| Word | What it means |
|---|---|
| Twisted pair | two copper wires twisted together to cut noise |
| Shielded | wrapped in metal foil or mesh against noise |
| Interference | unwanted signals that spoil the real signal |
| Coaxial | a cable with a copper core, a shield and a plastic coat |
| Fibre-optic | a cable of thin glass strands that carry light |
| Attenuation | a signal getting weaker over distance |
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Twisted pair: UTP and STP
UTP means unshielded twisted pair. It has four pairs of copper wire inside a plastic coat. It has no metal wrap. It is cheap and bends easily, so most offices and homes use it.
STP means shielded twisted pair. It has the same wires and a metal wrap. The wrap blocks interference. It costs more and is stiffer. It is used near motors, lifts and heavy machines.
Coaxial and fibre-optic cable
Coaxial cable has a copper core, a layer of plastic, a metal shield and an outer coat. It carries TV aerial signals and cable broadband into homes.
Fibre-optic cable carries light along glass strands. It is very fast, works over many kilometres and ignores electrical interference. It costs more and needs special tools. Glass can crack if you bend it too far.
The four cables side by side
| Cable | Carries | Strong point | Weak point | Used for |
|---|---|---|---|---|
| UTP | Electricity | Cheap and easy | Picks up noise | Office desks, home |
| STP | Electricity | Blocks noise | Dearer and stiffer | Factories, lift rooms |
| Coaxial | Electricity | Good shield | Bulky, not for new office wiring | Cable TV, CCTV |
| Fibre-optic | Light | Fast, far, no noise | Costly, fragile | Between buildings, backbone |
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