Cat5 Cable Pin Assignment

How to wire your own ethernet cables and connectors.

What You Need:

  • Ethernet Cable - bulk Category (Cat) 5, 5e, 6, 6a or higher ethernet cable
  • Wire Cutters - to cut and strip the ethernet cable if necessary
  • For Patch Cables:
    • 8P8C Modular Connector Plugs ("RJ45")
    • Modular Connector Crimper ("RJ45")
  • For Fixed Wiring:
    • 8P8C Modular Connector Jacks ("RJ45")
    • 110 Punch Down Tool
  • Wire Stripper
  • Cable Tester

About the Cable:

You can find bulk supplies of ethernet cable at many computer stores or most electrical or home centers. You want UTP (Unshielded Twisted Pair) ethernet cable of at least Category 5 (Cat 5). Cat 5 is required for basic 10/100 functionality, you will want Cat 5e for gigabit (1000BaseT) operation and Cat 6 or higher gives you a measure of future proofing. You can also use STP (Shielded Twisted Pair) for extra resistance to external interference but I won't cover shielded connectors. Bulk ethernet cable comes in many types, there are 2 basic categories, solid and braided stranded cable. Stranded ethernet cable tends to work better in patch applications for desktop use. It is more flexible and resilient than solid ethernet cable and easier to work with, but really meant for shorter lengths. Solid ethernet cable is meant for longer runs in a fixed position. Plenum rated ethernet cable must be used whenever the cable travels through an air circulation space. For example, above a false ceiling or below a raised floor. It may be difficult or impossible to tell from the package or labelling what type of ethernet cable it is, so peal out an end and investigate.

Here is what the internals of the ethernet cable look like:

Internal Cable Structure and Color Coding

Inside the ethernet cable, there are 8 color coded wires. These wires are twisted into 4 pairs of wires, each pair has a common color theme. One wire in the pair being a solid or primarily solid colored wire and the other being a primarily white wire with a colored stripe (Sometimes ethernet cables won't have any color on the striped wire, the only way to tell which is which is to check which wire it is twisted around). Examples of the naming schemes used are: Orange (alternatively Orange/White) for the solid colored wire and White/Orange for the striped cable. The twists are extremely important. They are there to counteract noise and interference. It is important to wire according to a standard to get proper performance from the ethernet cable. The TIA/EIA-568-A specifies two wiring standards for an 8-position modular connector such as RJ45. The two wiring standards, T568A and T568B vary only in the arrangement of the colored pairs. Tom writes to say "...sources suggest using T568A cabling since T568B is the AT&T standard, but the US Government specifies T568A since it matches USOC cabling for pairs 1 & 2, which allows it to work for 1/2 line phones...". Your choice might be determined by the need to match existing wiring, jacks or personal preference, but you should maintain consistency. I've shown both below for straight through cabling and just T568B for crossover cabling.

About Modular Connector Plugs and Jacks:

The 8P8C modular connectors for Ethernet are often called RJ45 due to their physical ressemblance. The plug is an 8-position modular connector that looks like a large phone plug. There are a couple variations available. The primary variation you need to pay attention to is whether the connector is intended for braided or solid wire. For braided/stranded wires, the connector has sharp pointed contacts that actually pierce the wire. For solid wires, the connector has fingers which cut through the insulation and make contact with the wire by grasping it from both sides. The connector is the weak point in an ethernet cable, choosing the wrong one will often cause grief later. If you just walk into a computer store, it's nearly impossible to tell what type of plug it is. You may be able to determine what type it is by crimping one without a cable.

Modular connector jacks come in a variety styles intended for several different mounting options. The choice is one of requirements and preference. Jacks are designed to work only with solid ethernet cable. Most jacks come labeled with color coded wiring diagrams for either T568A, T568B or both. Make sure you end up with the correct one.

Here is a wiring diagram and pin out:

Modular Connector Plug and Jack Pin Out

Ethernet Cable Pin Outs:

There are two basic ethernet cable pin outs. A straight through ethernet cable, which is used to connect to a hub or switch, and a crossover ethernet cable used to operate in a peer-to-peer fashion without a hub/switch. Generally all fixed wiring should be run as straight through. Some ethernet interfaces can cross and un-cross a cable automatically as needed, a handy feature.

Standard, Straight-Through Wiring Diagram(both ends are the same):

Straight-Through Ethernet Cable Pin Out for T568A Straight-Through Ethernet Cable Pin Out for T568B

Crossover Cable Wiring Diagram(T568B):

Crossover Ethernet Cable Pin Outs

+Note: The crossover ethernet cable layout is suitable for 1000Base-T operation, all 4 pairs are crossed.

How to wire Ethernet Patch Cables:

  1. Strip off about 2 inches of the ethernet cable sheath.
  2. Untwist the pairs - don't untwist them beyond what you have exposed, the more untwisted cable you have the worse the problems you can run into.
  3. Align the colored wires according to the wiring diagrams above.
  4. Trim all the wires to the same length, about 1/2" to 3/4" left exposed from the sheath.
  5. Insert the wires into the RJ45 plug - make sure each wire is fully inserted to the front of the RJ45 plug and in the correct order. The sheath of the ethernet cable should extend into the plug by about 1/2" and will be held in place by the crimp.
  6. Crimp the RJ45 plug with the crimper tool.
  7. Verify the wires ended up the right order and that the wires extend to the front of the RJ45 plug and make good contact with the metal contacts in the RJ45 plug
  8. Cut the ethernet cable to length - make sure it is more than long enough for your needs.
  9. Repeat the above steps for the second RJ45 plug.

How to wire fixed Ethernet Cables:

  1. Run the full length of ethernet cable in place, from endpoint to endpoint, making sure to leave excess.
  2. At one end, cut the wire to length leaving enough length to work, but not too much excess.
  3. Strip off about 2 inches of the ethernet cable sheath.
  4. Align each of the colored wires according to the layout of the jack.
  5. Use the punch down tool to insert each wire into the jack.
  6. Repeat the above steps for the second RJ45 jack.

If an ethernet cable tester is available, use it to verify the proper connectivity of the cable. That should be it, if your ethernet cable doesn't turn out, look closely at each end and see if you can find the problem. Often a wire ended up in the wrong place or one of the wires is making no contact or poor contact. Also double check the color coding to verify it is correct. If you see a mistake or problem, cut the end off and start again. A ethernet cable tester is invaluable at identifying and highlighting these issues.

When sizing ethernet cables remember that an end to end connection should not extend more than 100m (~328ft). Try to minimize the ethernet cable length, the longer the cable becomes, the more it may affect performance. This is usually noticeable as a gradual decrease in speed and increase in latency.


Power over Ethernet (PoE):

Power over Ethernet has been implemented in many variations before IEEE standardized 802.3af. IEEE 802.3af specifies the ability to supply an endpoint device with 48V DC at up 350mA or approximatlely 16.8W. IEEE 802.3at updates the PoE standard to supply up to 600mA or approximately 28.8W, it is often known as PoE+. The device must be capable of receiving power on either the data pairs [Mode A] (often called phantom power) or the unused pairs in 100Base-TX [Mode B]. PoE can be used with any ethernet configuration, including 10Base-T, 100Base-TX or 1000Base-T. Power is only supplied when a valid PoE endpoint is detected by using a low voltage probe to look for the PoE signature on the endpoint. PoE power is typically supplied in one of two ways, either the host ethernet switch provides the power, or a "midspan" device is plugged in between the switch and endpoints and supplies the power. No special cabling is required. Power over Ethernet Power Delivery

Protocol Details:

ProtocolStandardSymbol EncodingSymbol Rate (Mbaud)Data EncodingData Bits per SymbolPairs per ChannelPairs UsedNyquist Frequency Bandwidth (MHz)Minimum Cable Category
10Base-TIEEE 802.3iManchester10None112103
100Base-TXIEEE 802.3uMLT-31254B5B4/51262.55
1000Base-TIEEE 802.3ab4D-PAM5125None24462.55e (5)1
2.5GBase-TIEEE 802.3bzDSQ128 (2D-PAM16)200LDPC(1723,2048), 64B/65B, CRC83.125441005e2
5GBase-TIEEE 802.3bzDSQ128 (2D-PAM16)400LDPC(1723,2048), 64B/65B, CRC83.125442006 (5e)2
10GBase-TIEEE 802.3anDSQ128 (2D-PAM16)800LDPC(1723,2048), 64B/65B, CRC83.125444006a (6)3
25GBase-TIEEE 802.3bqDSQ128 (2D-PAM16)2000LDPC(1723,2048), 64B/65B, CRC83.12544100084
40GBase-TIEEE 802.3bqDSQ128 (2D-PAM16)3200LDPC(1723,2048), 64B/65B, CRC83.12544160084
Data Rate = Symbol Rate x Data Bits per Symbol x Pairs per Channel
The combination of the Symbol Encoding and Data Encoding determines how many Data Bits per Symbol there are.
1. Designed to work on most Cat 5 ethernet cable, Cat 5e specifications ensure 1000Base-T operation.
2. Although designed for Cat 5e/6, not all cabling will be usable at the full range, especially for 5GBase-T on Cat 5e.
3. Reduced range when used with Cat 6 (55m), Cat 6a supports the full 100m range. Some Cat 5e may support operation at reduced distance.
4. 30m range.

Cable Category Details:

Cable CategoryRated Nyquist Frequency Bandwidth (MHz)Common Uses
1NoneTelephone Wiring
21Telephone Wiring
316Telephone Wiring, 10Base-T
420Token-Ring, 10Base-T
5100100Base-TX, 10Base-T
5e1001000Base-T, 100Base-TX
62501000Base-T, 100Base-TX
8200025GBase-T, 40GBase-T
Increasing category levels are backward compatible.
Manufacturers will often test and certify their ethernet cable well beyond the standards.
1. Category 7/7a cabling does not use RJ45 connectors.

Related Reading Material

  • Get IEEE 802 - Ethernet Standards
  • Charles Spurgeon's Ethernet Website
  • Network Connection Speeds Reference
  • Fiber Optic Connector Reference
  • Ethernet: The Definitive Guide
  • Interconnections: Bridges, Routers, Switches, and Internetworking Protocols (2nd Edition)
  • The All-New Switch Book: The Complete Guide to LAN Switching Technology
  • TCP/IP Illustrated
  • UNIX Network Programming

Ethernet Cable Types, Performance & Pinout: Cat 5, 5e, 6, 6a, 7, 8 etc

Various cables are used for carrying Ethernet: current common types include Cat 5, 5e, Cat 6, 6a, 7 and Cat 8 and the RJ45 connector is widely used

Ethernet IEEE 802.3 Includes:
Ethernet introduction     Standards     Ethernet data frame structure     100 Base T     Gigabit Ethernet, 1GE     Cables     How to buy Ethernet cables     Power over Ethernet, PoE    

There are many Ethernet cables that can be bought. Often these cables are supplied free with equipment that uses Ethernet connectivity in some way or another.

There are several different varieties of Ethernet cable that can be obtained: speed variations, crossover cables, Cat 5, Cat 5e, Cat6, etc..

Normally Ethernet cables will be bought and there is no major need to understand what is inside or on the connectors, although it can be both interesting and helpful on some occasions. Even so, an understanding of the different types of Ethernet cable and the maximum lengths that should be used is helpful.

The commonly used cables: Cat 5, Cat 5e, Cat 6 all have different levels of performance, and therefore to is necessary to buy or select the right cable for the right application.

Categories for Ethernet cables

A variety of different cables are available for Ethernet and other telecommunications and networking applications. These cables that are described by their different categories, e.g. Cat 5 cables, Cat-6 cables, etc, which are often recognised by the TIA (telecommunications Industries Association) and they are summarised below:

  • Cat-1:     This is not recognised by the TIA/EIA. It is the form of wiring that is used for standard telephone (POTS) wiring, or for ISDN.
  • Cat-2:     This is not recognised by theTIA/EIA. It was the form of wiring that was used for 4Mbit/s token ring networks.
  • Cat-3:     This cable is defined in TIA/EIA-568-B. It is used for data networks employing frequencies up to 16 MHz. It was popular for use with 10 Mbps Ethernet networks (100Base-T), but has now been superseded by Cat-5 cable.
  • Cat-4:     This cable is not recognised by the TIA/EIA. However it can be used for networks carrying frequencies up to 20 MHz. It was often used on 16Mbps token ring networks.
  • Cat-5:     This is not recognised by the TIA/EIA. It is the cable that is widely used for 100Base-T and 1000Base-T networks as it provides performance to allow data at 100 Mbps and slightly more (125 MHz for 1000Base-T) Ethernet. Cat 5 cable is now obsolete and therefore it is not recommended for new installations.
  • Cat-5e:     This form of cable is recognised by the TIA/EIA and is defined in TIA/EIA-568-B.. It has a slightly higher frequency specification that Cat-5 cable as the performance extends up to 125 Mbps. It can be used for 100Base-T and 1000Base-t (Gigabit Ethernet). Cat 5e or enhanced is a form of Cat 5 cable manufactured t0 higher specifications although physically the same as Cat 5. It is tested to a higher specification.
  • Cat-6:     This cable is defined in TIA/EIA-568-B provides a significant improvement in performance over Cat5 and Cat 5e. During manufacture Cat 6 cables are more tightly wound than either Cat 5 or Cat 5e and they often have an outer foil or braided shielding. The shielding protects the twisted pairs of wires inside the Ethernet cable, helping to prevent crosstalk and noise interference. Cat-6 cables can technically support speeds up to 10 Gbps, but can only do so for up to 55 metres.
  • Cat-6a:     The “a” in Cat 6a stands for “Augmented.” The Cat 6a cables are able to support twice the maximum bandwidth, and are capable of maintaining higher transmission speeds over longer cable lengths. Cat 6a cables utilise shielded which is sufficient to all but eliminate crosstalk. However this makes them less flexible than Cat 6 cable.
  • Cat-7:     This is an informal number for ISO/IEC 11801 Class F cabling. It comprises four individually shielded pairs inside an overall shield. It is aimed at applications where transmission of frequencies up to 600 Mbps is required.
  • Cat-8:     These cables are still in development, but will be released in the foreseeable future to provide further improvements in speed and general performance.

Further descriptions of Cat-5 and Cat-5e cables are given below as these are widely used for Ethernet networking applications today.

Ethernet Cable Performance Summary
CategoryShieldingMax Transmission Speed (at 100 meters)Max Bandwidth
Cat 3Unshielded10 Mbps16 MHz
Cat 5Unshielded10/100 Mbps100 MHz
Cat 5eUnshielded1000 Mbps / 1 Gbps100 MHz
Cat 6Shielded or Unshielded1000 Mbps / 1 Gbps>250 MHz
Cat 6aShielded10000 Mbps / 10 Gbps500 MHz
Cat 7Shielded10000 Mbps / 10 Gbps600 MHz
Cat 8Details to be released later

Ethernet Cat 5 cable & pinout

Cat 5 cables or to give them their full name category 5 cable is the current preferred cable type for LAN network and telephone wiring where twisted pair cabling is required. Cat 5 cables consist of an unshielded cable comprising four twisted pairs, typically of 24 gauge wire. The terminating connector is an RJ-45 jack. In view of this these Cat5 network cables are often referred to as RJ45 network cables or RJ45 patch cables. Certified Cat-5 cables will have the wording "Cat-5" written on the side. As they conform to EIA/TIA 568A-5, this is written on the outer sheath. It is always best to use the appropriate network cables when setting up a network as faulty or not to standard cables can cause problems that may be difficult to identify and trace.

Cat5 network cable is now the standard form of twisted pair cable and supersedes Cat 3. The Cat 5 cables can be used for data speeds up to 125 Mbps, thereby enabling them to support 100Base-T which has a maximum data speed of 100 Mbps whereas the Cat-3 cable was designed to be compatible with 10Base-T. The Cat5 cable is able to support working up to lengths of 100 metres at the full data rate.

Where it is necessary to operate at higher speeds, as in the case of Gigabit Ethernet, an enhanced version of Cat 5 cable known as Cat 5e is often recommended, although Cat 5 is specified to operate with Gigabit Ethernet, 1000Base-T. Alternatively Cat 5e can be used with 100Base-T to enable greater lengths (up to 350 metres) to be achieved.

The wires and connections within the Cat 5 or Cat 5e cable vary according to the applications. A summary of the signals carried and the relevant wires and connections is given in the table below:

RJ-45 / Cat 5 / Cat 5e Pinout & Wiring
Mode A
Mode B
1 White / green   +TX +TD +BI_DA 48 V out  
2 Green   -TX -TX -BI_DA 48 V out  
3 White / orange   +RX +RX +BI_DB 48 V return  
4 Blue Ring     +BI_DC   48 V out
5 Blue / white Tip     -BI_DC   48 V out
6 Orange   -RX -RX -BI_DB 48 V return  
7 White / brown       +BI_DD   48 V return
8 Brown       -BI_DD   48 V return

In the table, TX is transmitted data, and RX is received data. BI_Dn is bi-directional data, A, B, C, and D.

Ethernet Cat 5 crossover cables

There are a number of different configurations of cable that may be employed according to the equipment and the requirement. The most common type are the straight through cables which are wired in a 1 to 1 configuration. However Cat-5 crossover cables are also required on occasions.

Typically a Cat-5 cable used to connect a computer (PC) to a switch will be a straight through cable. However if two computers or two switches are connected together then a Cat5 crossover cable is used.

Many Ethernet interfaces in use today are able to detect the type of cable, whether it is a straight through or crossover cable, and they are able to adapt to the required format. This means that the requirement for Cat-5 crossover cables is less than it might otherwise be.

When using Cat-5 Ethernet crossover cables, they are not marked with the fact that they are crossover cables. Accordingly it is often wise to mark them to avoid confusion later.

A variety of different cables are seen connecting different Ethernet elements together. Cat5, Cat5e and Cat6 are all seen. The cables use the cost efficient but effective RJ45 patch connector and using this, these Ethernet cables are able to link or patch multiple items of Ethernet based equipment together. On some occasions where specialised connectivity is needed crossover cables may be required - these sold be clearly marked as such as they may get used elsewhere unknowingly and cause the connection not to work. Apart from this using Cat 5, Cat5e and Cat 6 Ethernet cables is very easy and there are normally very few issues.

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