Cat 5 Cable Pin Assignments

Category 5 cable, commonly referred to as Cat 5, is a twisted pair cable for computer networks. The cable standard provides performance of up to 100 MHz and is suitable for most varieties of Ethernet over twisted pair. Cat 5 is also used to carry other signals such as telephony and video.

This cable is commonly connected using punch-down blocks and modular connectors. Most Category 5 cables are unshielded, relying on the balanced line twisted pair design and differential signaling for noise rejection.

The category 5 specification was deprecated in 2001 and is superseded by the category 5E specification.

Cable standard[edit]

The specification for category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95.[1] These documents specify performance characteristics and test requirements for frequencies up to 100 MHz.

The cable is available in both stranded and solid conductor forms. The stranded form is more flexible and withstands more bending without breaking. Patch cables are stranded. Permanent wiring used in structured cabling is solid-core. The category and type of cable can be identified by the printing on the jacket.[2]


Cable types, connector types and cabling topologies are defined by TIA/EIA-568-B. Nearly always, 8P8C modular connectors (often referred to as RJ45 connectors) are used for connecting category 5 cable. The cable is terminated in either the T568A scheme or the T568B scheme. The two schemes work equally well and may be mixed in an installation so long as the same scheme is used on both ends of each cable.

Variants and comparisons[edit]

The category 5e specification improves upon the category 5 specification by revising and introducing new specifications to further mitigate the amount of crosstalk.[4] The bandwidth (100 MHz) and physical construction are the same between the two,[5] and most Cat 5 cables actually meet Cat 5e specifications, though they are not specifically certified as such.[6] The category 5 was deprecated in 2001 and superseded by the category 5e specification.[7]

The category 6 specification improves upon the category 5e specification by improving frequency response and further reducing crosstalk. The improved performance of Cat 6 provides 250 MHz bandwidth and supports 10GBASE-T (10-Gigabit Ethernet) for distances up to 55 meters.[7] Category 6A cable provides 500 MHz bandwidth and supports 10GBASE-T for distances up to 100 meters. Both variants are backwards compatible with category 5 and 5e cables.


Category 5 cable is used in structured cabling for computer networks such as Ethernet over twisted pair. The cable standard provides performance of up to 100 MHz and is suitable for 10BASE-T, 100BASE-TX (Fast Ethernet), and 1000BASE-T (Gigabit Ethernet). 10BASE-T and 100BASE-TX Ethernet connections require two wire pairs. 1000BASE-T Ethernet connections require four wire pairs. Through the use of power over Ethernet (PoE), power can be carried over the cable in addition to Ethernet data.

Cat 5 is also used to carry other signals such as telephony and video.[8]In some cases, multiple signals can be carried on a single cable; Cat 5 can carry two conventional telephone lines as well as 100BASE-TX in a single cable.[9][10][11][12][13] The USOC/RJ-61 wiring standard may be used in multi-line telephone connections. Various schemes exist for transporting both analog and digital video over the cable. HDBaseT(10.2 Gbit/s) is one such scheme.[14]


The use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and crosstalk from other pairs.


Outer insulation is typically polyvinyl chloride (PVC) or low smoke zero halogen (LSOH).[citation needed]

FPFoamed polyethylene
FEPTeflon/fluorinated ethylene propylene
FFEPFoamed Teflon/fluorinated ethylene propylene
AD/PEAir dielectric/polyethylene
LSZH or LS0HLow smoke, zero halogen
LSFZH or LSF0HLow smoke and fume, zero halogen

Bending radius[edit]

Most Category 5 cables can be bent at any radius exceeding approximately four times the outside diameter of the cable.[22][23]

Maximum cable segment length[edit]

The maximum length for a cable segment is 100 m per TIA/EIA 568-5-A.[24] If longer runs are required, the use of active hardware such as a repeater or switch is necessary.[25][26] The specifications for 10BASE-T networking specify a 100-meter length between active devices.[27] This allows for 90 meters of solid-core permanent wiring, two connectors and two stranded patch cables of 5 meters, one at each end.[28]


Since 1995, solid-conductor UTP cables for backbone cabling is required to be no thicker than 22 American Wire Gauge (AWG) and no thinner than 24 AWG, or 26 AWG for shorter-distance cabling. This standard has been retained with the 2009 revision of ANSI TIA/EIA 568.[29]

Although cable assemblies containing 4 pairs are common, category 5 is not limited to 4 pairs. Backbone applications involve using up to 100 pairs.[30]

Individual twist lengths[edit]

The distance per twist is commonly referred to as pitch. Each of the four pairs in a Cat 5 cable has differing precise pitch to minimize crosstalk between the pairs. The pitch of the twisted pairs is not specified in the standard. Measurements on one sample of Cat 5 cable yielded the following results.[31]

  Pair color[cm] per turnTurns per [m]

Since the pitch of the various colors is not specified in the standard, pitch can vary according to manufacturer and should be measured for the batch being used if cable is being used in non-Ethernet situation where pitch might be critical.

Environmental ratings[edit]

LSZHCommunications low-smoke zero halogenNES‑711, NES‑713, MIL‑C‑24643, UL 1685
CMPCommunications plenumInsulated with fluorinated ethylene propylene (FEP) and polyethylene (PE) and jacketed with low-smoke polyvinyl chloride (PVC), due to better flame test ratings.CSA FT6[33] or NFPA 262 (UL 910)
CMRCommunications riserInsulated with high-density polyolefin and jacketed with low-smoke polyvinyl chloride (PVC).

UL 1666

CMGCommunications general purposeCSA FT4
CMCommunicationsInsulated with high-density polyolefin, but not jacketed with PVC and therefore is the lowest of the three in flame resistance.UL 1685 (UL 1581, Sec. 1160) Vertical-Tray
CMXCommunications residentialUL 1581, Sec. 1080 (VW-1)

Some cables are "UV-rated" or "UV-stable" meaning they can be exposed to outdoor UV radiation without significant destruction.[citation needed]

Plenum-rated cables are slower to burn and produce less smoke than cables using a mantle of materials like PVC. Plenum-rated cables may be installed in plenum spaces where PVC is not allowed.[34]

Shielded cables (FTP or STP) are useful for environments where proximity to RF equipment may introduce electromagnetic interference, and can also be used where eavesdropping likelihood should be minimized.


  1. ^"Additional Transmission Performance Guidelines for 4-pair 100 v category 5 Cabling"(PDF). Retrieved 2013-05-12. 
  2. ^"Ethernet Cable Identification and Use". Donutey. Archived from the original on 2011-07-10. Retrieved 2011-04-01. 
  3. ^"ANSI/TIA/EIA-568-B.1-2001 Approved: April 12, 2001 ; Commercial Building Telecommunications Cabling Standard Part 1: General Requirements"(PDF).  090917
  4. ^"Understanding Cat - 5 Cables"(PDF). Satelliete & Cable TV. Retrieved 2013-01-05"." 
  5. ^"Cat5 Spec, cat6 specs, cat7 spec - Definitions, Comparison, Specifications". TEC Datawire. Retrieved 2013-01-05"." 
  6. ^"Comparison between CAT 5, CAT 5e, CAT 6, CAT 7 Cables". 
  7. ^ ab"Voice and Data Cabling & Wiring Installations". Retrieved 2013-05-12. 
  8. ^"Transmitting video over CAT 5 cable". EE Times. 2005-06-08. Retrieved 2013-12-07. 
  9. ^"Hack your House: Run Both Ethernet and Phone Over Existing Cat 5 Cable". Retrieved 2016-08-15. 
  10. ^"LAN and Telephones". zytrax. October 21, 2015.  
  11. ^"Cable Sharing in Commercial Building Environments: Reducing Cost, Simplifying Cable Management, and Converging Applications onto Twisted-Pair Media". Siemon. Retrieved 2014-04-28. 
  12. ^"RJ45/RJ11 Network Cable Splitters for Ethernet and Phone Line Sharing".  
  13. ^"ATS 10/100 Base T Splitter Adapters". Retrieved 2014-08-17. 
  14. ^HDBaseT Alliance (January 9, 2013). "HDBaseT Alliance Shows the Future of Connected Home Entertainment at CES 2013". Retrieved 2017-10-31. 
  15. ^ abcdefghijk"SuperCat OUTDOOR CAT 5e U/UTP"(PDF). Archived from the original(PDF) on 2012-03-16. 
  16. ^ ab"Transmission Line Zo". 
  17. ^The characteristic impedance of a transmission line is given by . There are two important transition frequencies related this equation: and . Typically we have and the corner frequency (or break frequency) is defined as because at frequencies greater than the familiar "lossless" relation for characteristic impedance holds true to excellent approximation. Unfortunately neither of the terms corner frequency nor break frequency are consistently used in the literature. Most often these frequencies are not given any special name, and the topic itself is glossed over in most modern texts. Refer to Jim Brown. "Transmission Lines at Audio Frequencies, and a Bit of History"(PDF). Audio Systems Group, Inc.  and the references given within.
  18. ^ ab"Wire Gauge and Current Limits Including Skin Depth and Strength". PowerStream. Retrieved 2013-05-12. 
  19. ^IEEE 802.3at-2009 Table 33-11
  20. ^"Copper Data Cables"(PDF). p. 6. Archived from the original(PDF) on 2006-06-25. 
  21. ^"UTP-STP Cable"(PDF). Retrieved 2016-08-18. 
  22. ^"Selecting coax and twisted-pair cable". Electronic Products. Archived from the original on 2009-02-01. 
  23. ^"Category 5". Archived from the original on 2013-06-01. Retrieved 2013-05-12. 
  24. ^"The Evolution of Copper Cabling Systems from Cat 5 to Cat 5e to Cat 6"(PDF). Panduit. 2004-02-27. Archived from the original(PDF) on 2013-03-14. Retrieved 2013-05-12. 
  25. ^"UTP technology"(PDF). Extron Electronics. 2001. Retrieved 2013-05-12. 
  26. ^"CAT 5e Cable Wiring Schemes". B&B Electronics. Archived from the original on 2012-10-05. 
  27. ^"IEEE Std 802.3-2008". Institute of Electrical and Electronics Engineers. 2008. Table 13-1 
  28. ^"Horizontal Cabling". The Network Encyclopedia. Retrieved 2013-05-12. 
  29. ^"ANSI/TIA/EIA-568-B.2-2001, Commercial Building Telecommunications Cabling Standard"(PDF). p. 6 ¶4.3.2. 
  30. ^As noted in ANSI/TIA/EIA-568-B-2 standard for backbone applications
  31. ^Brooke Clarke, "CAT 5 Wire Measurements", Transmission Line Zo vs. Frequency, retrieved 2017-08-12 
  32. ^"Technical Information"(PDF). Belden. p. 22.20. Archived from the original(PDF) on 2006-10-20. 
  33. ^"CSA Flame Test Ratings". Retrieved 2013-05-12. 
  34. ^"What are the differences between PVC, riser and plenum-rated cables?". Archived from the original on 2011-07-13. 
Partially stripped cable showing the four twisted pairs (eight wires).

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


Leave a Reply

Your email address will not be published. Required fields are marked *