A Guide to Ethernet Cables

For this example, a laptop will be connected to the internet via an internet router modem. The Ethernet cable connector is first plugged into the Ethernet socket on the laptop or device's RJ45 socket (Registered Jack 45). The other end of the cable is plugged into the router modem.

Straight-Through Cable and Crossover Cable

• Straight-through cable is the most commonly used type - used to connect unlike devices together such as desktop PC to printer or games console to internet router
• Crossover cable - used to connect like devices such as laptops to laptops

Most modern devices auto-detect the cable type and configure accordingly, but it is worth noting that older devices may not have this capability.

Ethernet cables are used for connecting together devices for the transfer of broadband data.  A hard-wired connection is made between devices known as a LAN (Local Area Network). This method of connection offers a more reliable and faster speed transfer rate than some alternatives such as Wi-Fi connections. 

They can be used to connect portable devices like laptops, printers, and scanners. They can also be hard-wired into building structures to provide internet connection access from one room to another and throughout the whole building using Ethernet wall sockets.

Available in various categories, Cat5 cables, Cat6 cables, and Cat7 cables. Cat cable simply stands for Category of Cable. The Cat number ascends in order of cable speed and performance. The highest Cat number cables offer the fastest network traffic speed.

The cable construction contains 4 twisted pair cords sheathed with either a PVC jacket or an LSZH sheath. Shielding is applied to the twisted pairs by wrapping foil or twisted braid around them. 

The types of cable available are:

• UTP - Unshielded Twisted Pair
• STP - Shielded Twisted Pair
• U/UTP - Unshielded cable, Unshielded Twisted Pair
• F/UTP - Foil shielded cable, Unshielded Twisted Pair
• U/FTP - Unshielded cable, Foil shielded Twisted Pair
• S/FTP - braided shielded cable, Foil shielded Twisted Pairs

TP is twisted pair, U is Unshielded, F is foil shielded and S is braided shielded.

The benefits of using shielded cables are apparent when the cables are used in an environment where there is a lot of electrical noise present (EMI Electro-Magnetic Interference), or where there is a particularly long run. When installing Ethernet cables, it's advisable to separate them from power cables.

In such environments, interference finding its way to the twisted pair carrying important data is not desirable since it can interrupt and corrupt the data which in turn slows down the transfer of the data. The shielding reduces interference and noise permeating onto the internal cables resulting in a more reliable and faster data stream.

Shielding also reduces crosstalk. Crosstalk is where the unwanted signals from one twisted pair electromagnetically transfer to the adjacent pair causing internal interference and hence a reduction in performance and speed.

Cable length is an important consideration. The maximum length recommended when using a standard Cat5 Ethernet cable is 100m. However, it should be noted that the length of the cable should always be kept to the absolute minimum that is required. If the cable needs to be longer than 100m, then fibre optic cables should be considered.

Speed and performance may suffer as the cable run gets longer. Electrically noisy environments are more likely to affect performance on longer runs since more of the cable is exposed to external interference.

When using fast transfer internet speeds on long runs, Cat5e, Cat6 or above Cat cables are recommended.

There are many Ethernet cable types - and several considerations in choosing the correct cable for a particular application. Some of which include:

• Which devices are being connected together via Ethernet cable
• What are the transfer speed requirements
• How much Electrical interference (EMI) will be present in the installation environment
• How flexible does the cable need to be
• How long does the cable need to be

The straight-through type of Ethernet cable is by far the most popular and most commonly used. When connecting unlike devices together a straight-through standard cable should be used. For example, when connecting together a laptop to a printer or when connecting a games console to a router modem or switch.

A crossover cable is usually needed to connect together two similar devices such as a laptop to a laptop.

If only a short cable is required a patch cable may suffice to make the connection between devices. Ethernet cable adapter and couplers or an Ethernet cable splitter are available if there is a need to extend or connect to a further device.

Ethernet cable speed can vary. Faster data transfer requirements should be married with higher category cables. Cat5 Ethernet cables will suffice for most connections between devices.

Cat5 cables have a specified maximum run length of 100m and provide 100 Mbps speed performance. On the other hand, Cat7 cables will transmit up to (10Gbs) 10000 Mbps at 100m. A vast improvement in transfer speed.

The cost versus performance, length of run and environment should be carefully considered when buying a particular category of cable.

A foil or braid shielded cable should be utilised where there is a high expectation of electrical noise and interference. A shielded cable will be a better option in a fixed installation when connecting one Ethernet wall socket to another, as this type of installation is more likely to encounter electrical noise than a shorter-run portable cable might.

Appliances such as fluorescent light fittings or electrical motors tend to produce electrical noise and can interfere with internet data transfer. The effect of the interference is worsened with longer cable runs and could impact overall performance and transfer speed. Installing a shielded Ethernet cable would minimise the risk of interference in these scenarios, particularly for long cable runs.

Lower category unshielded Ethernet cables are generally thinner and more flexible than the shielded ones. Flexibility is more useful where the cable is used in portable devices and where the cable needs to be moved regularly. The less flexible shielded cables are best utilised in fixed position installations.

Choose a length of cable carefully. Shorter Ethernet cables tend to be less prone to external interference and offer better transfer speeds than longer ones.

Ethernet cables can be tested using an Ethernet cable tester. These are capable of testing cables and local area network (LAN) connections.

As you may have noticed, an Ethernet cable isn’t necessarily a one-size-fits-all solution - device types and environment are big considerations when selecting the right category and type. Looking to buy an Ethernet cable?