Twisted Pair — Copper Ethernet Cables
Twisted pair is the standard for LAN wiring. Four pairs of copper wires are twisted together inside the cable — the twisting reduces electromagnetic interference (EMI) between pairs (crosstalk) and from external sources. The category (Cat) rating determines maximum speed and bandwidth.
The most common cable exam question: "A technician needs to run a cable 80 metres to support 10 Gbps. Which category is required?" The answer is Cat6a — not Cat6. Cat6 only supports 10 Gbps up to 55 metres. At 80 metres, Cat6 falls back to 1 Gbps. Cat6a supports 10 Gbps for the full 100-metre standard run.
Memory trick: Cat6 = 10G at 55m. Cat6a = 10G at 100m. The "a" buys you the extra distance.
UTP vs STP — Shielding
| Type | Full Name | Construction | Use Case |
|---|---|---|---|
| UTP | Unshielded Twisted Pair | No metallic shielding around pairs or cable — relies on twisting alone for noise rejection | Standard office and home LAN — cheaper, easier to terminate, most common |
| STP | Shielded Twisted Pair | Metallic foil or braid shield around individual pairs or the entire cable | Industrial environments, areas with high EMI (near motors, fluorescent lights, elevator shafts), Cat7 |
| F/UTP | Foil shielded, unshielded pairs | Foil shield around all pairs together, individual pairs unshielded | Common STP variant — Cat6a shielded versions often use this construction |
Fiber Optic Cable
Fiber optic cables transmit data as pulses of light through glass or plastic strands — immune to EMI, capable of much higher speeds and longer distances than copper. Two major types, differentiated by the diameter of the glass core:
| Property | Single-Mode | Multimode |
|---|---|---|
| Core size | 8–10 µm (tiny) | 50 or 62.5 µm (larger) |
| Light source | Laser | LED or VCSEL |
| Distance | Up to 100+ km | Up to ~550 m (OM4) |
| Cost | Higher (laser transceivers) | Lower (LED transceivers) |
| Cable colour | Yellow | Orange or aqua |
| Use case | WAN, ISP backbone, long campus | Data centre, campus backbone, building-to-building |
Fiber Connectors
| Connector | Type | Exam Note |
|---|---|---|
| LC (Lucent Connector) | Small form factor, push-pull latch — most common in modern data centres and SFP transceivers | Most common fiber connector on the A+ exam — small, used in SFP/SFP+ ports on switches and NICs |
| SC (Subscriber Connector) | Square, push-pull snap-in connector — larger than LC, older standard | "Square connector" — used in older fiber infrastructure, still common in campus and WAN applications |
| ST (Straight Tip) | Round bayonet-style connector, twist-lock — older standard | "Pointy/round tip with a twist" — found in legacy multimode installations, less common now |
| MT-RJ | Duplex connector — carries both transmit and receive in a single small connector body | Less common — appears occasionally on A+ as a legacy connector type |
Coaxial Cable
Plenum vs Riser vs PVC — Fire Ratings
Cable jacket ratings determine where a cable can legally be installed based on fire safety. This is heavily tested on the A+ exam:
| Rating | Where It's Used | Fire Properties | Cost |
|---|---|---|---|
| Plenum | Plenum spaces — above drop ceilings and below raised floors where HVAC air circulates. Required by fire code in these spaces. | Low smoke, low toxicity when burned. Air-handling spaces can spread smoke throughout a building — plenum cable won't poison occupants. | Most expensive |
| Riser | Vertical runs between floors — inside conduit in walls or dedicated riser shafts | Flame-retardant — won't carry flame between floors, but produces more smoke/toxic fumes than plenum | Mid-range |
| PVC | General purpose — inside walls (not plenum, not riser), short patch cables, desktop connections | No special fire rating — burns and produces toxic smoke. Not suitable for plenum or riser spaces. | Cheapest |
You can always substitute a higher-rated cable in a lower-rated space but never the reverse. Plenum can go anywhere. Riser can replace PVC in riser spaces. PVC cannot be used in plenum or riser spaces.
The A+ exam scenario: "A technician needs to run cable above a drop ceiling in an office building. Which cable jacket is required?" → Plenum — the space above drop ceilings is always a plenum space.
Copper Connectors
| Connector | Used With | Exam Note |
|---|---|---|
| RJ-45 | Ethernet (Cat5e, Cat6, Cat6a) — 8 pins, 8 conductors (8P8C) | The standard Ethernet connector — all twisted pair LAN connections use RJ-45 |
| RJ-11 | Telephone lines — 6 pins, 2–4 conductors (6P2C or 6P4C). Smaller than RJ-45 | Phone jack — looks like a smaller RJ-45. DSL modems connect to the wall with RJ-11. |
| F-type | Coaxial cable (RG-6, RG-59) — screw-on threaded connector | Cable TV and cable internet — the connector on the back of a cable modem or TV |
| BNC | Coaxial cable — bayonet twist-lock connector | Legacy thin Ethernet (10BASE2), CCTV cameras, oscilloscopes |
Exam Scenarios
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Twisted Pair Categories — Specs You Must Memorise
CompTIA A+ and Network+ both require you to know the specifications for each Ethernet cable category. Cat5e (Cat 5 enhanced): supports up to 1 Gbps at 100 MHz over 100 metres. This replaced original Cat5 for Gigabit Ethernet and remains common in older installations. Cat6: supports up to 1 Gbps at 250 MHz and up to 10 Gbps at shorter distances (37–55 metres in 10GBASE-T applications). Cat6 has stricter crosstalk specifications than Cat5e and often includes a plastic divider (spline) between pairs. Cat6a (augmented): supports 10 Gbps at 500 MHz over the full 100-metre distance. Cat6a is physically larger and heavier due to additional shielding and is the current standard for new installations requiring 10 Gbps to the desktop. Cat7: 10 Gbps at 600 MHz, fully shielded (S/FTP), but uses a proprietary connector (GG45 or TERA) rather than standard RJ-45 and is rarely deployed. Cat8: 25–40 Gbps at 2000 MHz over 30 metres, designed for short datacenter runs between switches and servers.
The exam frequently asks: which cable category supports 10 Gbps over 100 metres? Answer: Cat6a. Which is most commonly used for modern office installations? Cat6a for new builds, Cat6 for upgrades where 10 Gbps at full length isn't required. The 100-metre maximum distance applies to all categories — this is the maximum segment length for Ethernet over twisted pair, regardless of cable category.
Fibre Optic Cable — Single-Mode vs Multi-Mode
Single-mode fibre (SMF) has a very thin core (8–10 microns) and carries light in a single path (mode) from a laser light source. Because there's only one light path, there's no modal dispersion — different light paths arriving at slightly different times — which allows single-mode to transmit data over extremely long distances (2–120 km depending on the application) at very high speeds. Single-mode is used for long-haul runs: between buildings on a campus, between datacenters, and in WAN links. The laser transceivers required for SMF are more expensive than multi-mode equipment.
Multi-mode fibre (MMF) has a larger core (50 or 62.5 microns) and carries light in multiple paths simultaneously, using LED or VCSEL (vertical-cavity surface-emitting laser) light sources. Multi-mode is cheaper and easier to work with but is limited to shorter distances — typically 300–400 metres for 10 Gbps applications (OM3/OM4 cable). Multi-mode is used within buildings and datacenters where distances are shorter and cost matters. The colour coding helps identify types: SMF is typically yellow, OM1/OM2 MMF is orange, OM3 MMF is aqua, OM4 MMF is magenta/violet.
On the exam: a company needs to connect two buildings 800 metres apart with 10 Gbps fibre. Multi-mode or single-mode? Single-mode — multi-mode's distance limitation is too short for 800 metres at that speed. A datacenter needs to connect server racks 50 metres apart with 40 Gbps fibre. Multi-mode or single-mode? Either works at that distance, but multi-mode is typically chosen for short datacenter runs due to lower cost.
Cable Connectors — What Goes on What
The connector is as important as the cable on the exam. RJ-45 is the standard 8-pin connector used for Ethernet (twisted pair) connections. All Cat5e through Cat6a cables terminate in RJ-45 at patch panels, wall jacks, and network equipment. RJ-11 is the smaller 4 or 6-pin connector used for telephone lines — if you see an RJ-11, it's phone, not Ethernet. Confusing RJ-45 and RJ-11 is a classic A+ trap question.
Fibre connectors vary by application. LC (Local Connector) is the most common in modern datacenter and enterprise applications — it's small, uses a latch mechanism, and is the connector on most SFP transceivers. SC (Subscriber Connector) is a push-pull square connector, common in older installations and some WAN equipment. ST (Straight Tip) is a bayonet-style twist-lock connector, now largely legacy. MTP/MPO is a high-density multi-fibre connector used in trunk cables for datacenter backbone — can carry 12 or 24 fibres in a single connector.
Coaxial cable uses F-type connectors for cable TV and internet (the threaded connector on the back of a cable modem), BNC connectors in older Thinnet Ethernet (10BASE2) and some CCTV applications, and N-type connectors for larger coax in antenna and wireless applications. On the exam, F-type and BNC are the most commonly tested coax connectors.
Cable Testing Tools
The exam expects you to match the right tool to the right cable testing task. A cable tester (continuity tester) sends a signal through each wire in a cable and verifies all connections are correct — it can detect open circuits (broken wire), shorts (two wires touching), and miswiring (wires crossed). A basic cable tester won't tell you the cable's performance characteristics, just whether it's physically intact. A TDR (Time Domain Reflectometer) sends a pulse down the cable and measures reflections to precisely locate faults — it can tell you a break or impedance mismatch is at exactly 47 metres from one end. TDRs are more expensive and used when you need to find faults in existing cable runs without pulling the cable.
A loopback plug (loopback adapter) connects a port's transmit pins to its receive pins, causing the port to receive the signals it transmits. Used to test whether a network port or NIC is functioning correctly — if the port passes a loopback test, the port itself is fine and the problem is elsewhere. A toner probe (fox and hound) consists of a tone generator that outputs a signal on one end of a cable and a probe that detects the signal to trace where the cable runs — useful for identifying which cable in a wall connects to which patch panel port.