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Ethernet Cables Explained
In 1973, Xerox PARC researcher Bob Metcalfe invented a high-speed networking system called Ethernet to allow computer workstations, servers and printers to share data and resources. Today, Ethernet connects hundreds of millions of devices in homes and businesses. In this article, we chart the evolution of the twisted pair category cable that forms the basis of many wired networks.
What is Category Cable?
The "Cat" in Cat5e, Cat6, etc. is short for "Category." Network cables are divided into categories based mainly on bandwidth (measured in MHz), maximum data rate (measured in megabits per second) and shielding.
For a time, this unshielded twisted pair (UTP) cable was the most common form of wiring for voice telephone systems in homes and offices. It consisted of two insulated copper wires twisted around each other and was designed for analog voice communications.
Category 2 cabling was capable of voice and data communications and was primarily used during the 1980s for IBM Token Ring networks. It supported a data transmission rate of 4 Mbps.
Introduced in the early 1990s, Category 3 cabling had four twisted pairs and was the first to support 10BaseT Ethernet networks as well as digital voice communications. It is still found in older buildings but its 10 Mbps data rate is considered too slow for modern networking.
Bandwidth vs. Data Rate
Bandwidth or frequency is a property of a cable and measures the rate at which a signal will cycle each second. 1 MHz is equal to 1 million cycles per second. Cat5 can handle up to 100 million signals a second (or 100 MHz). The cable category with the highest bandwidth is currently Cat8 with 2 billion (2 GHz) signals per second, 20 times as many as Cat5.
Data Rate and Bandwidth are related terms but they are not the same. Higher frequencies carry more 1s and 0s, allowing more bits of data to be transmitted per second. Cat5 cables have a one-to-one relationship between bandwidth and data rate: 100 MHz cable can transmit 100 Mb per second. Higher Category cables such as Cat8 encode the data so more bits can be transmitted in the same amount of time.
Frequency (and therefore data rate) can be increased by increasing the gauge of the conductor wires, adding more twists to the conductors, or adding shielding to each pair of conductors.
Like Cat3, Category 4 cable is typically found in older buildings where the cost of complete replacement is prohibitive. It had a data rate of 16 Mbps and was primarily used for IBM Token Ring networks.
Introduced in 1995, Category 5 cable has a data rate of up to 100 Mbps. It is used for standard 10BaseT and 100BaseT (Fast Ethernet) networks, and can distribute data, video and telephone signals at distances up to 100 meters (328 ft.). Cat5e is not an official designation but is used by manufacturers to describe an enhanced Cat5 cable that is capable of speeds up to 1 Gbps. Its higher data rate is achieved by increasing the number of twists, making it more resistant to crosstalk. Cat5e is recommended for new sub-Gigabit network installations.
In comparison to Cat5e, Cat6 cable provides greater bandwidth and data transfer rates up to 1 Gbps over 100 m, the same as Cat5e. However, at shorter distances of up to 37 m (121 ft.), Cat6 is able to achieve 10 Gbps speeds thanks to its improved shielding and higher bandwidth. Cat6 includes a physical separator called a "spline" between the four pairs to reduce crosstalk and foil shielding to reduce electromagnetic interference. Cat6 cabling is backward compatible with the Cat5/5e standard. Introduced in 2009, Cat6a is an "augmented" Category 6 cable with a bandwidth of up to 500MHz.
The Cat7 specification is a proprietary standard developed by a consortium of companies and is not endorsed by IEEE or TIA/EIA. While substantially similar to the performance characteristics of Cat6a, Cat7 cables features proprietary GG45 connectors and robust shielding. Cat7a (Category 7 Augmented) is a further refinement of Cat7, capable of 40 Gigabit speeds over 50 meters and 100 Gbps up to 15 meters. The proprietary nature of the Cat7 and Cat7a standards and lack of support from IEEE and EIA has resulted in a relatively small installed based for Cat7/Cat7a.
With a bandwidth of up to 2 GHz (2000 MHz) over 30 meters and a data rate of up to 40Gbs, Cat8 cable is ideal for switch-to-switch communications in a 25GBase T or 40GBase T network. Its conductors are wrapped in foil to virtually eliminate crosstalk and enable higher data rates. The result is a heavier gauge cable that is quite rigid and can be difficult to install in tight spaces. It still uses RJ45 connectors and is backwards compatible with previous standards.
|Category||Max. Data Rate||Bandwidth||Max. Distance||Usage|
|Category 1||1 Mbps||0.4 MHz||Telephone and modem lines|
|Category 2||4 Mbps||4 MHz||LocalTalk & Telephone|
|Category 3||10 Mbps||16 MHz||100 m (328 ft.)||10BaseT Ethernet|
|Category 4||16 Mbps||20 MHz||100 m (328 ft.)||Token Ring|
|Category 5||100 Mbps||100 MHz||100 m (328 ft.)||100BaseT Ethernet|
|Category 5e||1 Gbps||100 MHz||100 m (328 ft.)||100BaseT Ethernet, residential homes|
|Category 6||1 Gbps||250 MHz||100 m (328 ft.)
10Gb at 37 m (121 ft.)
|Gigabit Ethernet, commercial buildings|
|Category 6a||10 Gbps||500 MHz||100 m (328 ft.)||Gigabit Ethernet in data centers and commercial buildings|
|Category 7||10 Gbps||600 MHz||100 m (328 ft.)||10 Gbps Core Infrastructure|
|Category 7a||10 Gbps||1000 MHz||100 m (328 ft.)
40Gb at 50 m (164 ft.)
|10 Gbps Core Infrastructure|
|Category 8||25 Gbps (Cat8.1)
40 Gbps (Cat8.2)
|2000 MHz||30 m (98 ft.)||25 Gbps/40 Gbps Core Infrastructure|
What type of Ethernet cable should I buy for my home network?
Even with a speedy WiFi6 router, your connection to the Internet is usually the bandwidth bottleneck. Currently, the fastest Internet plans available from the major carriers offer download speeds of 1 gigabit per second (1,000 Mbps). If you already have the fastest Internet access available from your provider, use Cat6a cable. This will give you some headroom for future speed increases. For Internet download speeds up to a gigabit, Cat5e is a good choice. You'll save a little money over Cat6a and the thinner cable will be easier to install.
Ethernet Cable Length
The further a signal has to travel along a cable, the more it will degrade (a process known as attenuation) until it reaches the point where it can no longer be detected, or is too distorted to be interpreted by the receiving device. Attenuation can also be caused by noise due to electrical currents and radio frequencies. Cables with shielding to minimize noise will work reliably over greater distances.
The maximum length of a Cat5e or Cat6 Ethernet cable is about 295 ft. (90 m), plus up to 16 ft. (5 m) of patch cable on either end, for a total of 328 feet or 100 meters. Beyond this, the signal begins to degrade, reducing the speed and reliability of the connection. Good quality cable can support runs in excess of 100 meters but data transmission speed may be reduced. Higher data rates can also be achieved over shorter distances.
Ethernet Cable Shielding
Ethernet Cable and Connector Styles
Ethernet cables made from four twisted pairs are terminated using an 8-pin RJ45 connector. Older telephone cable based on two twisted pairs typically use RJ11 connectors.
The terms 8p8c (Eight Position, Eight Contact) and RJ45 are often used interchangeably but 8p8c actually refers to a category of connectors of which RJ45 is one. The modern RJ45 Ethernet connector is the most common example of an 8p8c connector.
GG45 (GigaGate 45) or ARJ45 (Augmented RJ45) is a connector originally developed by French cable company Nexans for use with Cat7 cable. GG45 connectors have 12 pins in total, 8 providing backwards compatibility with Cat6, and an additional 4 pins providing support for frequencies of up to 600MHz.
Why is an Ethernet cable connector called RJ45?
"RJ" stands for Registered Jack and refers to a standardized physical network interface. The "45" simply refers to the number of the interface in the standard specification.
Molded connectors are permanently attached to a cable using a manufacturing process called over-molding. The connector and cable are covered with a thermoplastic or silicon material to form one solid piece called a boot, making the cable more durable and able to withstanding a high number of insertion cycles.
Snagless connectors have a modified boot that protects the connector's lock from being accidentally snapped off. Snagless cables are typically used in situations where the cable is frequently connected and disconnected, such as a laptop-to-wall network connection.
Slim and Ultra-Slim Cables
Slim and Ultra-Slim cables have a diameter that's typically 30-50% less than that of a standard Cat6 cable. Manufactured from small gauge copper wire, the four-pair stranded cable increases airflow in crowded equipment racks, which helps keep components cool and functioning properly. The slim design also makes the cable lighter and easier to install in high-density racks, cable trays and ductwork.
Although not a common choice, flat cables have some unique characteristics that make them beneficial in certain applications. Flat cables have good heat dissipation and more evenly distribute physical loads on the cable. They also bend only through the wide faces whereas a conventional round cable bends in all directions.
A flat cable is a good choice if you need to carry an Ethernet patch cable around in your laptop bag. It is strong, light and will not tangle easily. Its flat shape makes it ideal for cable runs under carpet and behind baseboard.
Solid Core Cables
Network cables are available in stranded and solid wire formats. As the name suggests, a solid core cable uses one solid copper wire for each conductor, so a 4-pair cable will have a total of 8 solid copper wires. Solid conductor cable is easy to punch down, making it ideal for structured wiring applications.
In situations where a cable is repeatedly flexed or connected and disconnected, choose a stranded cable. For horizontal cable runs not subject to repeated movement, or for Power-over-Ethernet (PoE) and outdoor applications, use solid core cable.
What is a Crossover Cable?
There are two RJ45 pin configurations, referred to as T568A and T568B. The difference is the pin assignment for the green and orange pairs. T568A pinouts are the most commonly used but either will work so long as both ends of the cable are similarly wired. Cables with T568A wiring on one end and T568B on the other are known as "crossover" cables.
One of the factors limiting the length and data rate of Ethernet cable is the size of its conductors. Electrical current encounters greater resistance when transmitted over thinner wire. The larger the conductor, the easier it is for the electrons to pass through it resulting in lower resistance, lower signal loss and greater transmission distance.
The diameter or gauge of a cable's conductor is referred to using American Wire Gauge (AWG) standard sizes. For example, a 24 AWG solid conductor is 0.0201 inches in diameter. A 28 AWG conductor is 0.0126 inches in diameter, almost half the size. That's right, the smaller the AWG gauge, the bigger the conductor diameter.
|Cable Type||Typical Gauge||Diameter (inches)||Diameter (mm)|
|Slim Cat6||28 AWG||0.0126||0.3211|
|Ultra Slim Cat6||32 AWG||0.0080||0.2019|
Conductor gauge affects a cable's performance but is typically not the most important factor. Shielding and twist rate have more impact on signal strength and quality.
Ever wondered why an Ethernet cable uses twisted pairs of conductor wires? Early telephone lines were susceptible to interference from electrical wires that often shared the same utility poles. Engineers discovered that by swapping the position of the telephone wires every few poles (i.e. the left line became the right and the right became the left), they could reduce distortion. This technique of wire transposition was the first use of twisting, albeit with a very loose twist rate of about six turns per mile.
In 1881, Scotsman and AT&T co-founder Alexander Graham Bell used the same technique to create the first twisted pair. By the turn of the 20th century, twisted pair cable was widely used for transmission of signals on voice telephone lines.
Today, twisting conductor pairs is a common way to minimize signal interference and crosstalk, and increase cable performance. The twist rate or "pitch" is usually measured as the number of twists per inch or centimeter.
Twist Rate is not specified in the IEEE or TIA category cable standards and is left to the manufacturer to decide. Cat5e typically has a twist rate of 4-5 twists per inch whereas Cat6 cables have a twist rate of 5 or more twists per inch. To further reduce crosstalk, not all conductor pairs in a cable will have the same twist rate.
Jackets protect the cable's conductors from physical damage, moisture and ultraviolet light. When installing cable in walls, ceilings and under floors, it is important to use cables that meet the local code requirements (usually based on the NFPA's National Electric Code). The three basic ratings for both cable types are general purpose, riser and plenum-rated.
|Jacket Rating||Description||Applications||Acceptable Substitute|
|CM/CMG||Communications, General Purpose||
In-room cable runs.
Not for use in risers and plenum.
A riser is a vertical space, typically inside walls and between floors
May be required due to insurance or contractual clauses
Plenum is space above and below floors typically occupied by heating and air conditioning ductwork
Air ducts and plenums above and below floors.
May be required due to insurance or contractual clauses.
LDPE (low-density polyethylene)
Buried or exposed to moisture or UV light.
Cable runs up to 50-ft.
PoE allows both power and data to be delivered over a single, solid core category cable. This makes it ideal for networking IP devices like security cameras, access control readers, wireless access points (WAPs), sensors and lighting that require DC power and a data network connection. PoE gives you the flexibility to install devices where you need them without having to worry about access to AC power.
A Brief Overview of Power over Ethernet (PoE)
UL has developed a Limited Power Certification for Power-over-Ethernet (PoE) applications. The LP designation, first introduced in 2015, indicates that a cable has been tested under "reasonable worst case installation scenarios" and is capable of carrying the stated current without exceeding the temperature rating of the cable. The LP designation is particularly important in PoE++ applications where power exceeds 60 watts.
Exterior-grade CMX Ethernet cable is waterproof and resistant to drying and cracking after long-term exposure to the sun. It can also be buried in the ground without a conduit. Also consider cable and hooded connectors with an IP68 rating.
Plenum is the space above or below a room that provides a way for air to return to a building's HVAC system. A riser is a vertical shaft between floors for electrical wiring, water pipes, and voice or data cabling. In the event of a fire, it's critical that cabling in these areas does not promote the spread of smoke and toxic fumes.
When selecting cable to run through plenum or risers, look for products with a jacket rating of CMP (plenum) or CMR (riser). These cables have a higher degree of fire resistance and emit fewer toxic fumes compared to general purpose CM or CMG rated cables. In the US, the NFPA's National Electrical Code (NEC) guidelines requires CMP or CMR cabling for plenum or risers and compliance may be a contractual or legal requirement. Because CMP cables have a higher fire resistance, you can use CMP in risers but you cannot use CMR cable in plenum spaces.
The jacket on these cables is constructed using an antibacterial material that is 99.9% effective in inhibiting Escherichia coli (E. coli) and Staphylococcus aureus (staph). This added protection makes these cables an ideal solution for high-touch applications and in environments where bacterial infection is of particular concern, such as medical facilities, schools, process manufacturing and restaurants/kitchens.
Choosing Ethernet Cables
What is the difference between Cat5 and Cat6?
Cat6 and Cat6a cables are more expensive than Cat5e so it's important to know what you're getting for your money. For cable runs up to 50-ft, Cat6 is capable of 10 Gbps vs. 1 Gbps for Cat5e. For longer runs, Cat5e and Cat6 should give similar performance.
Should I upgrade from Cat5e to Cat6?
Upgrading to Cat6 makes sense if the equipment on either end is capable of 10 Gbps. For example, core network connections between switches, routers or bridges would benefit from the higher bandwidth.
Are Cat8 cables worth the extra money?
Cat8 is designed for switch-to-switch communications in 25G and 40G networks. Residential and commercial projects outside the data center would be better using Cat6a cable. Not only is it less expensive, it's also easier and faster to install.
Can you mix Cat5 and Cat6 cable in a network?
There's no problem in mixing Cat5e and Cat6 cable in the same network so long as you don't create a bottleneck. Use Cat6 in the parts of your network where fast data transfer is important, such as between a switch and a router.
Are all Cat6 cables the same?
All good quality cables that have been tested and certified by the manufacturer for a certain bandwidth and data rate are essentially the same. Shielded Cat6 and Cat6a cable will give you better performance than unshielded, particularly when cables must be run in close proximity to power lines or large electrical equipment.
Do cheap cables work just as well?
In a word, no. Category cables are made of solid or stranded copper but some companies sell cheap versions made with Copper Clad Aluminum (CCA), an aluminum conductor that is coated with copper. These cables are cheaper to manufacture but result in a weaker cable that does not perform as well.