Hardware · Topic 3 of 13
Network Cables and Connectors
Compare twisted pair Ethernet categories, coaxial cable, single mode and multimode fiber, and the RJ45, RJ11, F, LC, SC and ST connectors used with them.
- 5 min
- Twisted pair uses RJ45 connectors; the standard segment limit is 100 metres.
- Cat 5e is 1 Gbps, Cat 6 handles 10 Gbps over short runs, and Cat 6a does 10 Gbps at full length.
- Plenum cable is fire rated for air spaces; solid core is for walls and stranded for patch cables.
What it is
Network cables carry data between devices. The three main families are twisted pair copper, coaxial copper and fiber optic, and each has its own connectors, speed limits and best uses.
For the exam you must match a cable to its connector and to a scenario.
How it works
Twisted pair copper
Twisted pair cable holds four pairs of copper wires, with each pair twisted to cut interference. It ends in an RJ45 connector (Registered Jack 45, correctly an 8P8C modular plug). Unshielded twisted pair (UTP) is the common type.
Shielded twisted pair (STP) has foil or braid around the wires, which helps in places with much electrical noise.
Cables are rated in categories, and a higher category supports higher speeds.
| Category | Typical speed | Notes |
|---|---|---|
| Cat 5 | 100 Mbps | Old; seldom installed now |
| Cat 5e | 1 Gbps | Common and low cost |
| Cat 6 | 1 Gbps, and 10 Gbps over short runs | Tighter twist, may have a separator |
| Cat 6a | 10 Gbps at full length | Thicker, often shielded |
| Cat 8 | 25 or 40 Gbps over short runs | Meant for data centres |
The maximum length for a normal Ethernet copper segment is 100 metres (328 feet), including patch cables. Longer runs need a switch, repeater or fiber.
Two build choices matter. Solid core cable is stiff and suits fixed wiring inside walls, while stranded cable is flexible and suits patch cables.
Plenum rated cable has a jacket that gives off little smoke and toxic fumes in a fire, and building codes require it in air handling spaces, such as above ceilings. Ordinary polyvinyl chloride (PVC) cable is cheaper but is not used there.
Direct burial cable is built to run underground or outdoors without a conduit. It has a tough, waterproof jacket that resists ultraviolet (UV) light, and the inside is often filled with gel to keep moisture out. Ordinary indoor cable would absorb water and break down, so use direct burial rated cable for outdoor runs between buildings.
Telephone cable
RJ11 is a smaller modular plug with two or four wires, used for telephone lines and digital subscriber line (DSL) modems. It looks like an RJ45 plug, but it is narrower, and it does not fit an Ethernet port properly.
Coaxial cable
Coaxial cable has a central copper wire, an insulating layer, a shield and an outer jacket. It is used for cable television and cable internet.
| Type | Use |
|---|---|
| RG-6 | Cable television, satellite and cable internet; lower loss |
| RG-59 | Older and shorter video runs |
Cable television and broadband connections use an F connector, which screws onto the cable. A Bayonet Neill Concelman (BNC) connector twists and locks and appears on some video and older network equipment.
Fiber optic
Fiber sends data as pulses of light through glass or plastic strands. It is not affected by electrical interference, supports long distances and is harder to tap than copper.
| Type | Light source | Core | Use |
|---|---|---|---|
| Single mode (SMF) | Laser | Very thin | Long distances, such as between buildings or cities |
| Multimode (MMF) | Light emitting diode (LED) or low cost laser | Wider | Shorter links inside a building or campus |
Fiber connectors are small and come in several shapes.
| Connector | Name | Description |
|---|---|---|
| LC | Lucent Connector | Small, push and click latch; very common on switches |
| SC | Subscriber Connector | Square, push and pull; common in telecom |
| ST | Straight Tip | Round, twist and lock bayonet style; older multimode |
Because light travels in one direction in each strand, a typical fiber link uses two strands, one to send and one to receive.
Ethernet naming
Names such as 1000BASE-T and 10GBASE-T show speed and medium: the number is the speed, BASE means baseband signalling and T means twisted pair.
For a long run between buildings choose single mode fiber. For a run inside one building under 100 metres, twisted pair is cheaper and simpler.
Punch down and patch cabling
Fixed cable runs usually end in a wall jack or patch panel with punchdown connections, and short patch cables join them to devices. Keep untwisted wire at each end as short as possible to protect against interference.
What to remember for the exam
- Twisted pair uses RJ45 connectors; the standard segment limit is 100 metres.
- Cat 5e is 1 Gbps, Cat 6 handles 10 Gbps over short runs, and Cat 6a does 10 Gbps at full length.
- Plenum cable is fire rated for air spaces; solid core is for walls and stranded for patch cables.
- RJ11 is for telephone lines and DSL, and is narrower than RJ45.
- RG-6 coax with an F connector carries cable television and cable internet.
- Single mode fiber uses laser light for long distances; multimode is for shorter runs.
- LC, SC and ST are the common fiber connectors.
- Shielded cable reduces interference in noisy areas.
Common mistakes
Calling RJ11 and RJ45 the same. RJ11 is for telephone lines and is narrower than RJ45.
Ignoring the 100 metre limit. Beyond it, the signal weakens and the link can fail or run slowly.
Using PVC cable above ceilings. Air handling spaces need plenum rated cable.
Mixing single mode and multimode fiber. They need matching equipment and cable, and a mismatch causes poor or no connection.
Using solid core for patch cables. It can break when bent often. Stranded cable suits patch cords.
Check yourself
Which connector is used on Ethernet twisted pair cable?
The RJ45 connector.
Which fiber type is used for long distances?
Single mode fiber, which uses a laser.
What type of cable does the building code require above a suspended ceiling?
Plenum rated cable.
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