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Cat 5 Cabling Explained

Category 5 Cable

Partially stripped cable showing the four twisted pairs (eight wires).

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 un-shielded, 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The category 5 specification was deprecated in 2001 and is superseded by the category 5e specification.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

The specification for category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. 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.

Termination

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.
TIA/EIA-568-B.1-2001 T568A Wiring
Pin Pair Wire Color
1 3 1 Pair 3 Wire 1 white/green
2 3 2 Pair 3 Wire 2 green
3 2 1 Pair 2 Wire 1 white/orange
4 1 2 Pair 1 Wire 2 blue
5 1 1 Pair 1 Wire 1 white/blue
6 2 2 Pair 2 Wire 2 orange
7 4 1 Pair 4 Wire 1 white/brown
8 4 2 Pair 4 Wire 2 brown

 

TIA/EIA-568-B.1-2001 T568B Wiring
Pin Pair Wire Color
1 2 1 Pair 2 Wire 1 white/orange
2 2 2 Pair 2 Wire 2 orange
3 3 1 Pair 3 Wire 1 white/green
4 1 2 Pair 1 Wire 2 blue
5 1 1 Pair 1 Wire 1 white/blue
6 3 2 Pair 3 Wire 2 green
7 4 1 Pair 4 Wire 1 white/brown
8 4 2 Pair 4 Wire 2 brown

Variants and Comparisons

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 The category 5 was deprecated in 2001 and superseded by the category 5e specification.

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. 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.

Applications

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-T100BASE-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. 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. 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.

Characteristics

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

Electrical characteristics for Cat 5e UTP
Property Nominal Tolerance Unit
Characteristic impedance1–100 MHz 100 ± 15 Ω  
Characteristic impedance@ 100 MHz 100 ± 5 Ω  
DC loop resistance ≤ 0.188 Ω/m  
Propagation speed 0.64 c  
Propagation delay 4.80–5.30 ns/m  
Delay skew < 100 MHz < 0.20 ns/m  
Capacitance at 800 Hz 52 pF/m  
Inductance 525 nH/m
Corner frequency ≤ 57 kHz
Max tensile load, during installation 100 N  
Wire diameter 24 AWG (0.51054 mm0.205 mm2)  
Insulation thickness 0.245 mm  
Maximum current per conductor 0.577 A  
Operating temperature −55 to +60 °C  
Maximum operating voltage
(PoE uses max 57 V DC)
125 V DC  

Insulation

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

Example materials used as insulation in the cable
Acronym Material
PE Polyethylene
FP Foamed polyethylene
FEP Teflon/fluorinated ethylene propylene
FFEP Foamed Teflon/fluorinated ethylene propylene
AD/PE Air dielectric/polyethylene
LSZH or LS0H Low smoke, zero halogen
LSFZH or LSF0H Low smoke and fume, zero halogen

Bending Radius

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

Maximum Cable Segment Length

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

Conductors

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.

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

Individual wist Lengths

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.

Pair color [cm] per turn Turns per [m]
Blue 1.38 72
Green 1.53 65
Orange 1.78 56
Brown 1.94 52

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

United States and Canada fire certifications
Class Phrase Description Standards
LSZH Communications low-smoke zero halogen NES‑711, NES‑713, MIL‑C‑24643, UL 1685
CMP Communications plenum Insulated with fluorinated ethylene propylene (FEP) and polyethylene (PE) and jacketed with low-smoke polyvinyl chloride (PVC), due to better flame test ratings. CSA FT6 or NFPA 262 (UL 910)
CMR Communications riser Insulated with high-density polyolefin and jacketed with low-smoke polyvinyl chloride (PVC). UL 1666
CMG Communications general purpose CSA FT4
CM Communications Insulated 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
CMX Communications residential UL 1581, Sec. 1080 (VW-1)
CMH CSA FT1

Some cables are “UV-rated” or “UV-stable” meaning they can be exposed to outdoor UV radiation without significant destruction.

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.

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.