Download Copper Cabling

Cables and Cabling
Infrastructure
Part 1 – Basic Cable Construction
©PRGodin @ gmail.com
Updated Dec 2013
This Presentation
• This is a large presentation as it contains all the
materials for basic copper cable including:
▫
▫
▫
▫
▫
Terminology
Conductor styles
Basic cable structures
Jacketing
Performance characteristics including resistance,
capacitance, noise, throughput
▫ Grounding, twist characteristics
2
Cable? but wireless is the Future!
• Those wireless access points need to be interconnected
• Hard connections are more robust, more reliable, offer more control
and are more secure
• Wired has much higher data throughput, less latency
• Wired is unaffected by weather, line-of-sight, interference, etc
• Backbone connections need high performance only achieved with a
wired network
• CATV, ISP and Satellite communications need cables for distance.
• Limited wireless infrastructure
• Wired is less costly and easier to maintain in the long term
• Power can be delivered via wired
There will be fewer installations of wired ports at the user end but the
infrastructure will, in the foreseeable future, always be wired. There are far too
many advantages with wired networks.
3
Cable
• Cable is a package of conductors or strands
bound together.
• Communication cable construction, compounds
and structure affects its performance,
application, installation and durability.
4
Conductors
• There are many ways a copper conductor can be
structured.
• The two primary methods are:
▫ Solid
▫ Stranded
• There are other arrangements of conductors for
specific applications.
5
Solid Conductors
• Solid: Single strand of copper
▫ Lowest cost
▫ Very poor flexibility – only used in fixed
installations
Image: china-cablewire.com
6
Solid Conductors
• Bare Copper (BC): only copper
▫ Least expensive
▫ Susceptible to oxidization if exposed
Un-oxidized copper wire (left)
and oxidized copper wire
(right). Oxides have high
electrical resistance
Image: wikipedia
• Tinned Copper (TC): copper conductor with
a coating of lead/tin, or silver
▫ Protects the conductors from oxidization
▫ Easier to solder
▫ More expensive
7
Stranded Conductors
• Stranded: Multiple strands of copper twisted
as a single conductor
▫ Flexible but more expensive
• More individual strands increase flexibility and
cost.
Stranded Wire with High Strand Count
Image: Wiki CC
8
Stranded Conductors
• Stranded Bare Copper (SBC): strands of copper only
▫ Susceptible to oxidization if exposed
• Stranded Tinned Copper (STC): each strand is
coated with solder (Lead/Tin)
▫ Protects the conductors from oxidization
▫ Easier to solder
▫ More expensive
image: forums.nasioc.com (user submission)
9
• Copper Clad
▫ A different metal (typically steel) is
clad (covered) with copper.
▫ Used in high frequency
applications where tensile strength
is also desired.
▫ Many Coax cables have a copper
covered steel conductor.
Coax with Rigid Copper
Shield and Copper Coated
Steel Conductor
Image: PRGodin
Other Conductor Types
10
Other Conductor Types
Image: PRGodin
• Tubular (hollow tube)
▫ Specialized Applications
▫ Used in high frequency
applications (due to Skin Effect)
▫ Large diameter cables
▫ Difficult to physically handle
▫ Very expensive
Coax with Tubular
Conductor
11
Other Conductor Types
Image: www.maeden.com.tw
• Tinsel & Polyester
▫ Tinsel or polyester weave for high
flexibility devices such as headphones,
earphones and microphones.
▫ Difficult to terminate and solder.
Polyester Conductors
12
Other Conductor Types
Image: internet (multiple sources)
• Braid or Woven Wire
▫ Braid used for cable shielding
▫ Used for grounding applications
Woven or braided Wire
13
Other Conductor Types
Image: www.electrical-res.com
• Aluminum and other elements
▫ Conductors may use elements
other than copper:
 Aluminum






Lighter and cheaper
Typically larger gauge due to resistance
Used for electrical applications
Not as tolerant to flexing
Cannot be mixed with copper
Cannot be used for building wiring
Aluminum Wire
 Gold & Platinum (solid or plated)
 Used in semiconductor applications
 Other
14
Why Copper?
• Relatively abundant
• Good corrosion resistance
• Very malleable (ability to
bend and reshape)
• Relatively strong
• Very ductile (capability to
be made small)
• Excellent conductivity for
electricity and heat
Image: www.ccbda.org
15
Conductor Size
Wire sizing tool
Image: Wiki CC
16
Conductor Size
• Conductor diameter (size) is measured in American Wire
Gauge (AWG), or just Gauge (sometimes spelled Gage)
• Conductor size reduces with an increase in the gauge
number.
▫ a 24 AWG conductor is much smaller than a 12 AWG
conductor.
• Typical sizes
▫ Data communications: 20 to 28 AWG
▫ Electrical 18, 16, 14 and 12 AWG (Residential and
automotive)
▫ Much larger for industrial applications.
17
Conductor Size - Units
• AWG is considered an “imperial” unit
• Conductor sizes may be referred to by a metric
value that represents cross-sectional area in
square millimetres (mm2)
• A 20 AWG wire is 1029 circular mils. This is
between 0.6 mm2 and 0.5 mm2 in metric format.
• Conversion tables are available on line.
18
Gauge Tools
19
Conductor Size - Stranded
• Stranded conductors are referred to by
both the overall AWG of the bundle,
and the number and gauge of the
individual conductors.
▫ Example: a “7x32” stranded
conductor is made up of 7 strands of
32 gauge wire twisted together to
make up a 24 AWG sized conductor
24 AWG
Cross-section of a
“7x32” conductor
• More small-gauge strands makes the
conductor more flexible but also makes
it more expensive.
20
Jacketing Compounds
Jacket Extrusion Unit (Training Model)
Image: Wiki CC
21
Jacketing Compounds
• The more popular cable jacket compounds used today are:
▫ PVC (polyvinyl chloride): A versatile and inexpensive
compound, used for many indoor cables.
▫ PE (Polyethylene): Excellent electrical and environmental
properties. Used for outside jacketing and as a dielectric
for coax.
Teflon: Excellent electrical and
temperature properties. Nonflammable. Used in extreme
temperature environments or
Figure 4-33: Image of a tied-lace Teflonwhere fire immunity is desired
jacketed cable bundle on NASA’s Curiosity
such as alarm cable. Expensive. Rover in 2012 (with specks of Martian dust

in the background). Image: NASA
22
Jacketing Compound – Outside
• Direct Burial and “outside plant” applications
▫ Low density polyethylene often used.
▫ Water Repellent: gel or gas filled, expanding gel
tape.
▫ Often require ducting or armor for mechanical
strength and rodent resistance.
▫ Must be terminated within a few meters of
building entrance due to fire regulations,
lightning protection and ease of handling.
23
Jacketing Compound – Outside
• Aerial Applications
▫ Air-filled or expanding gel tape for reduced weight.
▫ Requires a messenger cable for support. Can be lashed
to a separate messenger or manufactured in a “figure-8”
configuration.
▫ High UV and temperature resistance
24
Jacketing Compounds
• There are many other compounds such as rubber,
silicone and a variety of vinyls & plastics used in the
industry for indoor and outdoor applications.
• Each have a variety of physical and electrical
properties that make them the best choice in
certain environments.
• Refer to vendor catalogs or web sites for more
information.
25
Making Jacketed Wire
• A large copper rod is warmed (not melted)
• The copper rod is forced through a succession of dies
▫ Dies are made of very hard material
▫ Each die reduces the copper’s diameter by ~30%
▫ Small wire gauges need to pass 30 to 40 dies
• Jacketing is then applied using an extrusion process
Plastic
(Pressure)
Insulated Wire
Wire
Water (cooling)
Image: PRGodin
26
Building Air
• Cables are often run in the same space as the
building air flow.
• The area above a suspended ceiling is usually the
return air from the living space and will be recirculated. This is known as an air plenum.
• Columns of space between floors, such as an
elevator shaft, are known as risers.
27
Cable Flammability
• Cable jacketing compounds can be a serious
problem should there be a fire.
▫ Burning cable jacketing produces highly toxic
smoke and gases. PVC releases hydrogen chloride
gas (hydrochloric acid) and other dangerous
compounds when it burns, including large
quantities of carbon monoxide.
▫ Cables run throughout a building often through
open tray in air plenums. Cables and trays must
have some resistance to spreading fire.
• All cables must meet fire codes and must be
installed within fire regulations.
28
Jacketing Compounds
• Environmental issues, installation location and
fire regulations dictate the jacketing required.
• In most indoor office locations, fire rating are
the main criteria:
▫ FT-1 rating for workstation cords
▫ FT-4/CMR/OFNR rating for most fixed
applications in most provinces
▫ FT-6/CMP/OFNP rating for installations in BC,
ON, PQ (check provincial code before installing).
29
Flammability (CSA)
• FT-1: Cable self-extinguishes after 60 seconds.
• FT-4: Chars for less than 1.5 meters.
• FT-6: Chars for less than 1.5 meters and produces
much less smoke. Will not sustain a flame.
• For more information see the National Electrical
Code (NEC), the Canadian Electrical Code (CEC)
or the International Electrotechnical Commission
(IEC).
30
Flammability Ratings
• The CSA (Canadian) and UL (American) communications cabling
standards were harmonized as a bi-national standard. The identification
of cable flammability for the US and Canada is as follows:
▫ MPP or CPP or CMP: Multi-Purpose Plenum or Communication
Plenum. FT-6 rated.
▫ MPR or CPR or CMR: Multi-Purpose Riser or Communication Riser,
for riser cable identification. FT-4 rated.
▫ MPG or CPG or CMG : Multi-Purpose General use or Communication
General use. FT-4 rated.
▫ CM, CMH or CMH: FT-1 rated.
31
Resources
• Belden Inc, a cable manufacturer, has excellent
information on jacketing compounds.
▫ www.belden.com
32
Cable Markings
Optical Cable markings for fire ratings. The markings include terms
such as OFNR & Riser, OFN & FT-4, and OFNP & Plenum.
Image: PRGodin
33
Cable Markings
• Communication cable jackets contain print that
typically includes many of these elements:
▫ Manufacturer
▫ Model Number
▫ Description (short form)
 #pairs or conductors
 Conductor characteristics
 Type of cable (may be an industry number)
▫ UL and/or CSA and/or ETL indication (may include registration
number)
▫ Manufacturing date
▫ Meter length marking
▫ Code compliance
34
Cable Markings
• Example of a cable marking:
Mohawk/CDT 25 PR 24 AWG (UL) C(UL) CMR or
MPR---- ETL Verified to TIA/EIA 568- A Cat 5---Patent Pending----M56753 B115-6 022922 ft
35
Elements of a Cable
36
Image: http://www.rictec.com.sg
Image: PRGodin
Definitions: Shielding
• Shielding: Reduces electrical
noise.
▫ Braided wires:
 Coverage expressed in % (can
never achieve 100% coverage).
 Helps to maintain cable shape.
Cable foil shield (STP cable)
image: www.customdesignedcable.co.uk
▫ Foil:
 Often polyester covered with a
conductor.
 Can achieve 100% coverage.
Cable Braid
37
Definitions: Shielding
• Rigid Tape: A thick metallic tape used for
electrical and mechanical reasons.
• Armor: Mechanical protection in the form of
interlocked rigid steel or aluminum.
Image: PRGodin
•Drain Wire: A conductor
that electrically connects to
the shield
Cable interlocking armour
38
Definitions: Structural
• Filler: Inert extra materials added to help the
cable maintain the proper shape.
• Strength member: An element mainly used to
maintain cable rigidity.
• Aramid Yarn or Kevlar®: Used for strength
(longitudinal or “pull”). Dupont Kevlar®.
39
Definitions: Structural
• Gel Tape: A tissue-like material that expands into a
gel-like substance when exposed to water.
Image: PRGodin
• Rip Cord or string: A string placed just inside a cable
jacket, used to cut the jacket material away. Usually
make of Dupont Kevlar®
•Twinned or Siamese: Two
cables joined as one at the
jacket.
Twinned
Cat 5 UTP
40
Cable Images
41
Cable – Twisted Pair
Unshielded Twisted Pair (UTP)
Screened Twisted Pair (ScTP)
Image: Wiki CC
42
Cable – Twisted Pair
Jacket
Filler
Foil Shield
Rip Cord (not shown)
Insulated
Twisted Pair
Conductors
Unshielded Twisted Pair (UTP)
Drain Wire
Screened Twisted Pair (ScTP)
Image: Wiki CC
43
Cable – Shielded Twisted Pair (STP)
Image: PRGodin
44
Cable – Shielded Twisted Pair (STP)
Foil Shield
(Individually
Shielded Pair)
Conductor Pairs
Braided Shield
Jacket
Image: PRGodin
45
General Multiconductor
Image: Wiki CC, PRGodin
46
Shielded Multi-conductor
Overall Foil Shield
Drain Wire
Braided Shield
Images: Wiki CC, PRGodin
47
Coax Cable
Images: Wiki CC, PRGodin
48
Coax Cable
Jacket
Braided Shield
Foil Shield
Dielectric
Copper coated steel conductor
Images: Wiki CC, PRGodin
49
Fiber Optic -Indoor Distribution
Primary use: interconnect panels and rooms within a building.
Higher density of fibers for size, some strain relief.
Image: PRGodin
50
Fiber Optic -Indoor Distribution
Aramid Yarn
(Kevlar)
Buffered fiber
strands
Rip Cord
Strength Member
Image: PRGodin
51
Fiber Optic -Indoor Distribution
Images: PRGodin
52
Fiber Optic – Indoor Breakout
Primary use: Interconnect panels, outlets, rooms within a building.
Used where good protection and connectorization is needed as
there is a strain relief and jacket for each strand.
Images: PRGodin
53
Fiber Optic – Indoor Breakout
Strength
Member
Rip Cord
Fiber Strand
Overall Jacket
Aramid
Yarn
Image: PRGodin
Buffered
Fiber
Strand
54
Outside Plant Fiber Cable
Images: PRGodin
55
Discussion points for Part 1
• What is the difference between a fiber optic breakout
cable and a fiber optic distribution cable?
• What fire rating is required for commercial installations
in Alberta? Is a certificate acceptable in the absence of a
cable marking?
• In what instance would a solid conductor be
inappropriate?
• Which is bigger: a “00” AWG or a “20” AWG conductor?
• Why are copper conductors sometimes “tinned”?
• What is a “7x32” conductor?
56
Cables and Cabling
Infrastructure
Part 2 – Cable Selection and Color Code
©PRGodin @ gmail.com
Updated Dec 2013
57
Selecting Cable
58
Selecting Cable
• The effectiveness of a communications infrastructure is
dependent on the cabling.
• It is important to consider several factors when selecting
telecommunications system cable.
The five basic cable characteristics are:
1.
2.
3.
4.
5.
cost;
size and scalability;
connectors; and
noise immunity;
throughput and bandwidth
59
Costs
• Generally, the better the performance the greater the cost.
• Economic factors such as availability, shipping, warranties
and the competitiveness of the marketplace.
• Installation costs are primarily based on the difficulty of
installation for cable, connectors and other elements such as
racks, conduit, etc... . Installation is typically the greatest cost.
• Manufacturing costs include complexity of the cable and the
price of raw materials such as copper and fiber.
• Must find balance between cost and needs (current and
future).
60
Size and Scalability
• The number of nodes, the distances between the
nodes and other physical constraints will
determine the type of cable and how the
installation is structured.
• Future intentions for growth (Moves, Adds and
Changes), and bandwidth requirements, both
current and future, will also have an impact on
the decision.
61
Connectors
• Connectors are based on the type of cable used
and are a large part of the cost of installation.
Connectorization must include testing (and
certification to standards).
• A decision can be made to install extra cables (or
extra strands of fiber) for termination in the
future.
62
Noise
• Noise immunity is the cable’s ability to deter
noise (EMI and RFI) that can distort data
signals.
• Noise in the environment can affect the selection
of cable types.
63
Throughput
• Throughput is the amount of data that media
carries during a given period and is measured in
megabits per second (Mbps) or megabytes per
second (MBps).
• It is a rate but is often referred to as a “speed”.
• In data communications, throughput is often
referred to as bandwidth.
64
Bandwidth
• In digital communications, bandwidth is defined
as the transfer capabilities of the media and is
also referred to in bits per second. It is a
measure of the media’s capacity, cited as a
maximum.
• In the Analog world bandwidth has a different
definition from the digital communication
world. Bandwidth is the difference between the
highest and lowest frequency that a media can
carry, measured in Hertz (Hz).
65
Bandwidth versus Speed
• The time it takes for a signal to go from the input to the output is
called the velocity of propagation. The speed of a cable (how fast a
signal goes from one end to another) is generally unrelated to its
bandwidth.
• Relative velocity of propagation (in % speed of light):
▫ Coax 85%
▫ UTP 68%
▫ Fiber Optics 66%
▫ Basic Control Wire 54%
66
Throughput vs Bandwidth
• Throughput and Bandwidth are similar terms. Both
have the same measurement unit, a bit rate, but
bandwidth is the theoretical maximum rate whereas
throughput is the actual bit rate achieved.
• Consumers usually refer to transfer rates as “speed”.
Although this is incorrect, the concept of throughput and
bandwidth are perhaps a little too difficult to explain to
the average user.
67
Baseband versus Broadband
• Baseband: operate at a single frequency. Most data
communication networks are baseband.
• Broadband: many communication signals at various
frequencies are present at the same time. Mass
communication systems operate as broadband. Examples
include the television channels present on a coaxial cable.
Tuner
68
Bandwidth
• In terms of cable selection, the bandwidth is an
important consideration for cable performance.
• Issues to address regarding bandwidth includes
the current and future uses for the network.




Data
Voice
Video
Combination
69
Communications
Cable Types
70
71
Unshielded Twisted Pair (UTP)
Image: Wiki CC
72
Unshielded Twisted Pair
UTP is the most common type of network cabling used today.
Advantages:
▫
▫
▫
▫
▫
Standards-Based
Inexpensive
Flexible
Universal
Small Diameter
Disadvantages:
▫ Limited performance over
distance
▫ Installation-related
factors affect performance
▫ Bandwidth limitations
▫ Susceptible to Noise
73
Unshielded Twisted Pair- Construction
• Pairs of twisted insulated conductors in an overall jacket.
• Configured in 4 and 25 pair configurations for structured
cabling.
▫ 23 or 24 AWG solid bare copper for fixed installations.
▫ 24 or 26 AWG stranded bare copper for patch cords.
• Configured in other pair counts for voice applications,
commonly referred to as PIC (Plastic Insulated
Conductor):
▫ 1, 2, 4, 5, 6, 8, 12, 25, 50, 75, 100, 150, 200, 300, 400, 600, 900,
1200, 1500, 1800, 2100, 2400, 2700, 3000, 3600 and 4200 pairs.
74
Twists
• Lay: The number of twists per length.
• Each pair must have a different lay to reduce
crosstalk. Generally, the more twists per foot for
the conductors, the better the performance of
the cable.
Lay
1 ft
75
ScTP and STP
• Shielded twisted-pair (STP)
▫ consists of individually insulated twisted pairs surrounded
by a metallic shielding that must be grounded.
▫ Although a high performance cable, it has disadvantages
and is not in the current cabling standards.
• Screened twisted-pair (ScTP)
▫ consists of insulated pairs of wires contained in a full foil
laminate shield
▫ superior immunity to radio frequency fields and reduced
crosstalk
▫ may be included in future TIA/EIA standards
76
UTP Categories
• UTP cable is classified into performance-based
categories.
• The specifications for the categories are defined in
the TIA/EIA 568C standard.
• Categories are added to and removed from the
standard as technology changes and improves.
77
Categories
Category
Data Rate
(Mbps)1
Comments
1
0.02
Telephone and Signal Wire
2
4
Early Token Ring networks
3
10
10Mbps Ethernet, still frequently used for telephone-only
installations (residential)
4
20
Latter Token Ring networks. Short-lived Category.
5
100
100Mbps (fast) Ethernet, ATM. Not recommended.
5e
100
Improved performance over Cat 5. Recommended.
6
1000
6a
10,0002
7
?
Gbts Ethernet . Recommended.
Recommended for new installations but expensive and thicker.
In discussion and lab testing. Likely ScTP with individually
shielded pairs or conductors.
1-Mbps = Mega bits per second, or 1 million bits per second.
2- Only achievable over considerably shorter distances
78
Mbps versus MHz
• Mega bits per second and Mega Hertz are
different.
• Ethernet data is encoded and the data doesn’t
produce only two logic levels. This encoding
reduces the frequency required to carry the data.
• 100Mbt Ethernet operates at an average
frequency of approximately 32MHz
79
Future - Twisted Pair
• Category 7
▫ 1GHz (Cat 6 = 250MHz, Cat 6a = 500MHz) Currently
in discussion. Requires a fundamental cable structural
change (UTP has achieved its limit with Cat 6/6a).
Will need a new connector. Class ‘F’ in Europe.
• SOHO - Small Office Home Office
▫ Standardization of cabling for the private sector- 4 pair
balanced copper- may combine data and multimedia50 meters- 1.2 GHz
• Category 8
▫ Not determined. Likely individual shielded twisted
pair with an overall shield
80
Future – Twisted Pair
• Changes that may take place:
▫ Shielding
 Overall, individual pairs or individual conductors
 May have a separate drain wire
▫ Distance
 May decrease the maximum distances
▫ Increased wire gauge
 Reduced resistance
▫ Increased size
 Better and thicker insulation (dielectric); may require separator
between pairs
▫ Different connector style (TERA, GG45 in Europe)
81
TERA and GG45 connectors.
The TERA connector may be used for
broadcast applications; the GG45 is
backward compatible with the 8pos mod plug
82
PIC Cable
•
•
•
•
Unshielded twisted pair
Plastic Insulated Conductor
Used for voice and low frequency communications
Does not perform within the Categories range and
is outside the cabling standard
• Can have very large pair counts (up to 4200)
• May be used indoors and outdoors (aerial or
buried)
83
UTP Color Code
84
Twisted Pair – Cable Colour Code
• There are five (5) primary colors and five (5) secondary
colors for multi-pair cable.
▫ TIP:
 Secondary color with a band of Primary colors.
 White - Red - Black - Yellow - Violet
▫ RING:
 Primary color with a band of secondary colors.
 Blue - Orange - Green - Brown - Slate
Important
85
White
Pair Tip Ring
1 White/Blue - Blue/White
2
White/Orange - Orange/White
3
White/Green - Green/White
4
White/Brown - Brown/White
5
White/Slate - Slate/White
86
Red
Pair Tip Ring
6 Red/Blue - Blue/Red
7
Red/Orange - Orange/Red
8
Red/Green - Green/Red
9
Red/Brown - Brown/Red
10
Red/Slate - Slate/Red
87
Black
Pair Tip Ring
11 Black/Blue - Blue/Black
12
Black/Orange Orange/Black
13
Black/Green - Green/Black
14
Black/Brown - Brown/Black
15
Black/Slate - Slate/Black
88
Yellow
Pair Tip Ring
16 Yellow/Blue - Blue/Yellow
17
Yellow/Orange - Orange/Yellow
18
Yellow/Green - Green/Yellow
19
Yellow/Brown - Brown/Yellow
20
Yellow/Slate - Slate/Yellow
89
Violet
Pair Tip Ring
21 Violet/Blue - Blue/Violet
22
Violet/Orange - Orange/Violet
23
Violet/Green - Green/Violet
24
Violet/Brown - Brown/Violet
25
Violet/Slate - Slate/Violet
90
91
UTP/PIC Color Code
TIP
RING
White
Red
Black
Yellow
Violet
Blue
Orange
Green
Brown
Slate
Pair
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Tip
White
Red
Black
Yellow
Violet
Ring
Blue
Orange
Green
Brown
Slate
Blue
Orange
Green
Brown
Slate
Blue
Orange
Green
Brown
Slate
Blue
Orange
Green
Brown
Slate
Blue
Orange
Green
Brown
Slate
92
Binders
• Cables of 50 pair and larger are grouped in 25
pair units and each wrapped with colored tape to
form “binder groups”.
• The binder groups (colored tape) follow the
same color code as the ring wire of each pair (ie
1st binder is blue/white. )
• See lab exercise for more information.
93
Coax Cable
Jacket
Braid Shield
Foil Shield
Dielectric
Image: PRGodin
Central
Conductor
94
Coaxial Cable Construction
• An inner copper conductor carries the data
• An insulating material called the dielectric holds the center
conductor. The dielectric has good electrical properties.
• A braided metal shield serves as a signal ground and also
helps retain the shape of the cable. A foil shield in some
cables offers more noise protection
• An overall jacket protects the cable and has markings.
95
Advantage of Coax
• There are fewer frequency restrictions with
coaxial cable
• All of the signal is contained within the coaxial
structure. Noise emissions is less of an issue.
• External noise is significantly reduced by the
shield.
• The impedance is relatively stable.
• Can transmit much higher frequencies than UTP
• Velocity of Propagation typically 85%
• Relatively easy to connectorize.
96
Disadvantages of Coax
• The shield of the coax, used as a reference voltage,
carries noise.
• Coax cable shields must be grounded properly.
• Not as adaptable to use for as many systems as
UTP.
• Generally not as flexible.
• Coax in data communications may make a
comeback but is outside of the standards at this
time.
97
Review Questions
• What term is used to describe the data carrying
capability of a communication cable?
• What factors help determine cable selection?
98
Cables and Cabling
Infrastructure
Part 3 – Technical Cable Performance
©PRGodin @ gmail.com
Updated Dec 2013
99
Electrical and Physical Specifications
• Copper cables such as UTP and Coax have
several important specifications that must be
considered.
• Technical performance issues include:
▫ Impedance (resistance, capacitance, inductance)
▫ Noise, shielding and grounding
100
Voltage, Current and Resistance
• Voltage can be defined as the degree of
attraction between electrons and positive ions.
Can be described as “pressure”.
• Current can be defined as the amount of
electrons that are flowing.
• Resistance can be defined as an opposition to
the flow of electrons. Resistance causes voltage
(“pressure”) drops.
101
Basic Model of an Atom
Electron (-)
Proton (+)
Neutron (no charge)
Nucleus
Orbit (path of the spinning electrons)
Basic Model of Current and Voltage
Electron Hole (+)
Electron (-)
Force of attraction (Voltage)
Flow (Current)
Positive Ion
V  IR
Basic Model of Ohm’s Law
Electron Hole (+)
Electron (-)
Force of attraction (Voltage)
Flow (Current)
Resistance to flow (Resistance)
Positive Ion
V  IR
Basic Digital Signals
• Basic systems work in a BINARY format ( a “1” or a “0” )
• Represented as a square wave (“+voltage” or “-voltage” over
a period of time)
• Signal must be above a threshold voltage to represent one
binary value and below a threshold voltage to represent the
other.
• Signal timing must be within a threshold for each bit to be
recognized.
+Voltage
Minimum Threshold
Unknown Zone
Maximum Threshold
- Voltage
Timing
105
Basic Digital Signal Problems
•
•
•
•
Noise (unwanted signal)
Impedance (reduced voltage)
Capacitance (timing errors)
Resistance (reduced voltage)
106
AC Signals
• The varying voltage values of a communication signal are
known as AC (Alternating Current).
▫ Sometimes referred to as varying DC, modulated DC or
other term
• AC signals may take various shapes.
▫ For digital communications they
generally take on square shapes
▫ For analog communications such as in
broadband they are generally sine
shapes
107
Resistance
• Resistance is the opposition to current flow.
• Resistance is present in all conductors.
• Resistance causes voltage drops in cable.
• Increasing the size of the conductor decreases
resistance.
108
Resistance
• Symbol:
• Letter Symbol: R
• Unit of Measure: Ohms (Ω)
▫ Typical: Ω, kΩ
Resistance of Conductors
Conductor resistance in circular
copper conductors
AWG
Ω per 100ft
(30.5 meters)
12
0.16
14
0.26
16
0.41
18
0.65
20
1.04
22
1.65
24
2.62
26
4.16
28
6.62
30
10.52
110
Induction
• Inductance
▫ Can be defined as the transference of electrical energy
from one conductor to another.
• Faraday’s law (1831)
▫ The voltage induced in a conductor is proportional to
the rate of change of magnetic lines of force that pass
through the conductor.
Faraday’s discovery of the relationship between electricity
and magnetism is often cited as the most important
discovery of the modern era.
111
Magnetism
• Principle:
▫ Magnetic flux lines are
established between the 2
poles of a magnet
▫ The quantity, density and
length of these lines
increases with:
N
S
 the characteristics of the
medium
 the strength of the magnet
Image: PRGodin
112
Electromagnetism
• Principle:
▫ Magnetic flux lines are
established when current
flows in a conductor
▫ The quantity, density and
length of these lines
increases with current.
▫ The direction of the flux
lines is determined by the
direction of the current.
Image: PRGodin
113
Electromagnetism
• Principle:
▫ If conductors are coiled, the flux
lines of the individual turns
combine and concentrate to create
a bar magnet.
▫ If AC current is applied, the
polarity of the magnet will reverse
N
S
 Note it takes time for the field to
collapse and re-establish itself in the
other direction.
 Inductance impedes current flow (XL).
 The effects of inductance increase with
frequency.
Image: PRGodin
114
Electromagnetic Induction
• Principle:
▫ Magnetic flux lines crossing a
conductor will induce current.
▫ There must be relative
motion, produced with AC.
▫ The quantity of lines that cross
the conductor over a period of
time will determine the induced
current.
▫ The direction of the current is
based on the polarity and
direction of the flux lines.
Image: PRGodin
Source Current
Induced Current
115
Induction and Noise
• The relative motion of the electromagnetic field
occurs when fields build up and collapse with AC
signals.
• Inductance causes problems with communication
cabling:
▫ External sources of noise (ingress)
▫ Adjacent sources of noise (within the cable)
▫ Generate noise (egress)
116
External Source: Ambient Noise
• Ambient Noise:
▫ Background, steady, predictable noise.
▫ Measuring the frequency of the noise may
help determine the source.
 60Hz = lighting, motors, electrical appliances,
electrical cabling, transformers, etc…
 100Hz to 20 MHz = switching power supplies,
electronic devices, telephone systems, video,
etc…
 > 20MHz = radio transmitters, cellular
telephones, etc…
117
External Source: Transient Noise
• Transient Noise:
▫ Irregular and unpredictable noise.
▫ Transient noise is often difficult to
pinpoint.
▫ Likely sources are switching circuits, such
as
 Elevators, photocopiers, welders, electrical
storms, static electricity, switching highcurrent devices, etc…
118
EMF, EMR, EMI, RFI and EMP
• EMF and EMR:
▫ Electro-Magnetic Field and Electro-Magnetic Radiation, generally
describes the strength of a magnetic field and its ability to induce current.
▫ May also refer to Electro-Motive Force (Voltage)
• EMI and RFI:
▫ Electro-Magnetic Interference and Radio Frequency Interference describe
undesired, induced electrical current. RFI applied to higher frequencies.
• EMP:
▫ Electro-Motive Pulse which is a sudden but short-lived increase in EMI or
RFI. Often destructive. EMP sources include electrical storms, solar
storms and weapons.
119
Twisted Pairs and Noise
• One conductor of a pair carries a signal and the other is
that signal’s reference. This serves to reduce the effect of
noise (Differential Voltage/Signaling)
• Two pairs are needed to communicate
▫ Transmit pair
▫ Receive pair
12V
V 12V
V
Voltage induced on
both conductors
Image: PRGodin
120
Noise on Twisted Pairs
• Principle: If noise is induced on one conductor, the
same amount of noise is induced on the other conductor.
The voltage between the two conductors remains the
same. Differential signaling systems have a built-in
cancellation effect.
10V
+12.5V
+2.5V
Input
5V
5V
-2.5V
Voltage induced on
both conductors
Output
+7.5V
Image: PRGodin 121
Internal Source: Crosstalk
• A regular source of noise is CROSSTALK, where
within a cable, one pair of signal-bearing
conductors induces a signal on an adjacent pair
of conductors.
122
Internal Source: Crosstalk
• Near End Cross Talk (NEXT) is a measurement of
transference of signal from one pair to adjoining pairs.
• It’s measured from the same end (near end) as where the
test signal is being injected.
Crosstalk
Image: PRGodin
123
Alien Crosstalk
• Alien crosstalk is noise from an
adjacent communication cable.
• Bundles of UTP cable can create
alien crosstalk.
• Recommendations are to not bundle
too many cables together for too
long a distance, or too tightly.
Image: PRGodin
124
Capacitance
• Capacitance is storage of an electrical charge, measured
in Farads.
• It is a property where two conductors separated by an
insulator can store an electrical charge if a voltage
difference exists between them.
• Capacitors are based on electrostatic principles where a
force of attraction or repulsion exists between charged
bodies.
125
Electro-statically charged particles
Image: PRGodin
126
Electronic Capacitors
• Electronic capacitors consist of
two conductors usually in the
form of plates, separated by an
insulator (dielectric).
Image: PRGodin
• Increasing the plate size can be
accomplished by rolling it up
into a smaller package, or
stacking plates.
127
Wires as a Capacitor
Conductor
--- --- --- ---
Insulation
Attraction
Insulation
+++ +++
+++ +++
Conductor
The charge is held on the wires because the different
charge polarities are electro-statically attracted to each
other. Without a conductive path connecting them, the
charge remains on the conductor.
Image: PRGodin
128
Factors Affecting Capacitance
Conductor Length (Plate size)
▫ Longer conductors means more charge can be held and higher
capacitance.
Separation between the conductors
▫ Larger separation between the conductors means less electrostatic attraction and lower capacitance.
The Insulator
▫ The insulating material between the conductors affects the
attraction and capacitance. PVC and other plastic materials have
lower capacity to concentrate electrostatic fields and hold a
charge.
129
Factors Affecting Capacitance
Permittivity is the ability of a material to concentrate
electrostatic flux. Measured and reported as dielectric
constant.
εr
Dielectric
Vacuum
1.0
Air
1.0006
Polyethylene
1.7 to 2.6
Teflon (FEP)
2.1
Polypropylene
1.5 to 2.3
Rubber
3.0
PVC
3.5 to 8
Polyurethane
7.1
Water
80.0
Sulfuric Acid
84-100
Relative permittivity of materials
(symbol ε, unit F/m)
The lower the
value the lower
the capacitance.
130
High and Low Capacitance
++++++++++++++
Conductor
+++++++++
Dielectric and
Electrostatic field
--------------High Permittivity
High Capacitance
Image: PRGodin
Conductor
--------Low Permittivity
Low Capacitance
131
Capacitance
• Symbol:
• Letter Symbol: C
• Unit of Measure: Farads (F)
▫ Typical: µF, ηF, ρF
132
Effect of Capacitance on Cable
• Capacitance causes signal deformation
Original Signal
Distorted signal
due to capacitance
• The effects of capacitance increase with
frequency. Capacitance is the greatest limiting
factor for high frequency performance.
Image: PRGodin
133
Reasons for Twists
• Reduces Crosstalk (the infringement of the signal from one wire pair
on another wire pair’s signal).
• Reduces Capacitance (the opposition to voltage changes).
• Improves Impedance (opposition to current)
• Each pair has a different lay, reducing the amount of direct contact
between conductor pairs, therefore reducing capacitance and
crosstalk. A divider may be present to keep the pairs separated.
Same lay = Regular contact
Cross-section of
Cat 6 with divider
Different lay = Less contact
Image: PRGodin
134
135
Noise Emissions
• The FCC (USA) has expressed concerns over
cable emissions (called ‘cable egress’). These
emissions may affect other communication
systems.
• Emissions are a data security risk. Signals may
be picked up and deciphered.
• Emissions are a loss of signal power.
136
Grounds
• A ground is a point or conductor that has zero electrical
potential, and is a reference point for signals.
• Grounds are important for signal transfer and for safety.
Grounds must be properly configured and used.
• Grounding is addressed in the TIA/EIA 607 standard.
137
Ground Types
• There are 3 basic types of grounds in electrical systems:
▫ Earth ground: primary role is safety. It is also the
absolute reference point for voltage. The potential of an
earth ground is considered 0 Volts.
▫ Chassis ground: usually used for safety and for cable
shielding. Has a potential of 0 Volts.
▫ Common ground: a point of reference for signals and
voltages. Not for safety. May have potential to other
grounds.
Chassis Ground
Earth Ground
Common Ground
138
Minimizing Noise
• Maintain electrical separation between the
communication cable and electrical appliances
and conductors (addressed in the standards).
• Employ shielded cable that is properly
grounded.
139
Grounding and Shielding
Electromagnetic Field
Metallic Shield
Induced Current
Improper grounding and shielding is a common source
of error in data cable installations.
140
Error: Ground Loop
• Ground Loops are multiple paths to ground.
• Ground loops interfere with the effectiveness of a ground.
▫ The different grounds may be at different potential,
drawing current through the shield.
▫ The voltage reference may not be at 0 Volts.
▫ Greater issue with coax cable
Other
equipment
Metallic Shield
Current
Example: One ground connection has more resistance than the other. Any
equipment on the ground system may use the cable shield as a path to the
lower resistance ground, creating noise on the cable.
141
Ground Potential Difference
Building frame
System 1
System 2
Building frame
• Ground potential differences cause serious data
communications problems. Here is an example:
ground resistance
Actual problem
encountered in Calgary
142
Grounding and Shielding
• Maintain a Single Ground Point
Metallic Shield
Induced Current
Proper Ground Connection
143
Grounding and Shielding
• Outdoor cable plants (OSP) require two or more
connections to ground
▫ Safety overrides communication quality issues
▫ Reduce problems by using low resistance ground
connections
▫ Follow engineering guidelines
Metallic Shield
Induced or Direct Current
Proper Outdoor Ground Connections
144
Reducing the Effect of Noise (1)
• Distance:
▫ Magnetic flux lines are less dense with distance from
the source. Maintain a separation from any sources of
noise, especially electrical cables. Addressed in the
TIA/EIA 568C standard.
▫ Reduce the length of cable
• Shielding:
▫ Employ shielded cable to either protect its conductors
from EMR, or reducing its emissions of EMR.
▫ Employ proper ground connection techniques.
 Low resistance path to ground
145
Reducing the Effect of Noise (2)
• Other:
▫ Use better quality cable
 highest category for UTP
 better shield coverage (other)
▫ Use the proper terminators if required
▫ Employ proper installation techniques
146
Questions
• What is the difference between capacitance and
inductance?
• How do the plastic insulators contained within a
cable affect its signal performance?
• How does the structure of a cable affect its
performance?
147
Impedance of a Cable
•
•
•
•
Cables contain Resistance, Capacitance and Inductance.
The total of these effects is called impedance.
Impedance is the resistance to alternating current.
The symbol is Z, the units are Ohms (Ω).
Electrical equivalent of a Cable
148
Cable Impedance
• The structure of the cable, its conductors plus
the dielectric determine the Characteristic
Impedance of a cable.
▫ For coax, typical values are 50, 75, and 93 ohms
▫ For UTP, typical value is 105 ohms
▫ Other cables will have different values
• It is very important to match the impedance of
the coax cable to the system requirements.
Signal reflection will result in poorly matched
cables.
149
Coax Cable Impedance
Designation
Z (Ω) Applications
Comments
RG58 /U or A/U
50
General instrumentation,
Arcnet
Solid conductor, large variety
of configurations
RG58 C/U
50
Ethernet Thinnet
Stranded conductor,
Foil/braid shield
RG59
75
Video, CATV, Broadband
Solid conductor
RG6
75
Video, CATV, Broadband
Solid conductor, better
performance than RG59
RG8
50
Ethernet Thicknet
Double layer of shielding, 12
AWG center conductor
RG62
93
IBM 3270, Arcnet
Air dielectric
RG22 B/U
(Twinax)
95
IBM 3X/AS400
Two conductors in dielectric
150
Reflection: Line Noise
• If the transmission line are not properly impedancematched to the system, some signal reflection will occur.
• On some cables (especially coax), if a terminator is not
present, the signal will reflect from the end of the
conductor, resulting in ringing. This echo causes
interference on the cable.
Image: PRGodin
151
Review Questions (1)
• Define the following terms:
▫ Attenuation:
▫ Bandwidth:
▫ Digital:
▫ Impedance:
152
Review Questions (2)
• Define the following terms:
▫ Ohm
▫ Amps
▫ Resistance
▫ Lay Length
153
Review Questions (3)
• Define the following terms:
▫ Capacitance
▫ Inductance
▫ Crosstalk
▫ Ambient
▫ Transient
154
End of Part 3
©PRGodin, Calgary, AB, Canada
Updated Dec 2013
155