Figure A-16 Bonding Properly installed bonding and grounding will accomplish the following: ■ Minimize electrical surge spike effects ■ Maintain the integrity of the electrical grounding
Trang 1Bonding involves providing a means for various wiring fixtures to interconnect with
the grounding system (see Figure A-16) It can be thought of as an extension of ground
wiring A device such as a switch or a router might have a bonding strap between its
case and a ground circuit to ensure a good connection
Figure A-16 Bonding
Properly installed bonding and grounding will accomplish the following:
■ Minimize electrical surge (spike) effects
■ Maintain the integrity of the electrical grounding plant
■ Provide a safer and more effective path to ground
Telecommunications bonds typically are used in the following ways:
■ Entrance facilities
■ Equipment rooms
■ Telecommunications rooms
Grounding and Bonding Standards
The National Electrical Code contains much information on grounding and bonding The
TIA/EIA standard on grounding and bonding, TIA/EIA-607-A, “Commercial Building
Grounding and Bonding Requirements for Telecommunications,” extends grounding
and bonding into the telecommunications structured cabling system TIA/EIA-607-A
specifies the exact interface points between the grounding system of a building and the
telecommunication equipment grounding configuration It supports a multi vendor,
Electrical Service Panel
6 AWG Ground for Telecommunications Cable and Equipment
Metallic Service Conduit
Approved Bonding Connector
Trang 2multi product environment for the grounding practices for various systems that may
be installed on customer premises It also specifies the necessary grounding and bond-ing configurations needed in the buildbond-ing to support this equipment
Lab and Workplace Safety Practices
Although cable installation is generally a safe profession, there are plenty of opportu-nities for being injured Many injuries are caused when installers come in contact with stray sources of voltage, called foreign voltages, such as lightning, static electricity, or other types of voltages caused by installation faults or induction currents that somehow find themselves onto network cables
When working in walls, ceilings, or attics, the first thing that should be done is to turn off power to all circuits that might pass through those work areas If it is not clear which wires pass through the section of the building being worked in, a good rule to follow is to shut off all power Never touch power cables Even if all power to the area has been shut off, there is no way to know whether circuits are still “live.”
Most countries have one or more agencies that develop and administer safety stan-dards Some of these are designed to ensure public safety; others are designed to pro-tect the worker Those that propro-tect the worker usually cover laboratory safety, general workplace safety, compliance with environmental regulations, and hazardous waste disposal
Workplace Safety
The following are guidelines for keeping a workplace safe:
■ Before beginning work, learn the locations of all fire extinguishers in the area
A small extinguishable fire can get out of control if no one is able to locate an extinguisher quickly
■ Always find out in advance what the local codes are Some building codes might prohibit drilling or cutting holes in certain areas, such as firewalls or ceilings The site administrator or facility engineer will be able to help determine which areas are off-limits
■ When installing cable between floors, use a riser-rated cable Riser cable is covered with a flame-retardant fluorinated ethylene propylene (FEP) jacket and, therefore, will not allow flames from one floor to use the cable to reach another floor
Trang 3■ Outdoor cables typically have a polyethylene jacket (PVC) Polyethylene burns
readily and gives off dangerous gases NEC codes state that polyethylene building entrance cables cannot be exposed more than 15 m (approximately 49 ft.) into a building If greater distances are required, the cable must be in metallic conduits
■ Consult the building’s maintenance engineer to find out whether there is
asbes-tos, lead, or PCB in the working areas If so, follow all government regulations in dealing with that material These materials are called hazardous for a reason No one’s health should be risked by working unprotected in these areas
■ Finally, if cable must be routed through spaces where air is circulated, be sure to
use a fire-rated cable (plenum-rated) The most common plenum cables are jack-eted with Teflon or Halar Plenum-grade cable does not give off poisonous gases when it burns, like regular cables, which have a polyvinyl chloride (PVC) jacket
Ladder Safety
Ladders come in many sizes and shapes to be used for many specific purposes They
can be made of wood, aluminum, or fiberglass, and are designed for either light or
industrial use The two types that are the most common are straight ladders and
step-ladders Regardless of the type or construction, be sure that the ladder has a label
certify-ing that it complies with specifications of the American National Standards Institute
(ANSI) and that Underwriters Laboratories (UL) lists it as passing its standards
■ Select the right ladder for the job Be sure that the ladder is long enough to work
from comfortably and is sturdy enough to withstand repeated use Fiberglass ladders most commonly are used in cable installation Although aluminum ladders are lighter, they are less stable and never should be used around electricity When working near electricity, only fiberglass ladders should be used
■ Inspect the ladder first Any ladder can develop a problem that can render it
unsafe Inspect ladders for loose or damaged rungs, steps, rails, or braces Make certain the spreaders on stepladders can be locked in place and that the ladder has safety feet that will provide more stability and reduce the chances of the ladder slipping while working Never use a ladder that is defective
■ Stepladders should be fully opened with the hinges locked Straight ladders should
be placed at a 4:1 ratio This means that the base of the ladder should be 0.25m (10 in.) away from the wall or other vertical surface for every 1m (3 ft.) of height
to the point of support If possible, secure a straight ladder as close to the point
of support as possible, to prevent shifting Ladders always should be placed on a solid, level surface
Trang 4■ Never climb higher than the second step from the top on a stepladder, or the third from the top on a straight ladder
■ Cordon off the work area with appropriate markers, such as traffic cones or caution tape Post signs so that people are aware of the ladder Lock or block any nearby door that might swing toward the ladder if it opens
Fiber-Optic Safety
Because fiber-optic cable contains glass, it is important to take appropriate precautions The scrap material is sharp and must be disposed of properly As with any glass product, when broken it, can cut or can splinter into tiny slivers that can get lodged in the skin These rules should be followed to avoid injury when working with fiber optics:
■ Always wear safety glasses with side shields
■ Place a mat or piece of adhesive on the table so that all glass shards that fall are more easily identified
■ Do not touch eyes while working with fiber-optic systems until hands have been cleansed thoroughly Similarly, do not handle contact lenses until hands have been washed thoroughly
■ Put all cut fiber pieces in a safe place and dispose of properly
■ If some of the material gets on clothing, use a piece of adhesive or masking tape
to remove it Use tape to remove shards from fingers and hands
■ No food or beverages in the work area should be allowed
■ Do not look directly into the end of fiber cables Some laser-driven devices could cause irreversible damage to the eye
Fire Extinguisher Use
Never attempt to fight a fire without knowing how to use a fire extinguisher Read instructions beforehand and check the valve In the United States, regulations state that fire extinguishers used in commercial buildings must be checked at regular inter-vals and replaced if they’re not in good working order
Fire extinguishers have labels that identify which kinds of fires they are designed to fight In the United States, these are called ratings Four different types of fires have been classified in the United States:
■ Class A fires involve ordinary materials, such as burning paper, lumber, card-board, plastics, and so on
■ Class B fires involve flammable or combustible liquids, such as gasoline, kero-sene, and common organic solvents used in the laboratory
CAUTION
If someone catches on
fire, remember the tip,
“Stop, Drop, and
Roll”:
• Stop, do not run
Fire spreads quickly
if a burning person
starts running If a
burning person
panics and runs
down the hall,
tackle that person.
• Drop to the floor.
Roll on the floor to
extinguish the flames.
Trang 5■ Class C fires involve energized electrical equipment, such as appliances, switches,
panel boxes, power tools, hot plates, and most other electronic devices Water is
a particularly dangerous extinguishing medium for Class C fires because of the risk of electrical shock
■ Class D fires involve combustible metals, such as magnesium, titanium,
potas-sium, and sodium These materials burn at high temperatures and react violently with water, air, and other chemicals
Personal Safety Equipment
Determine before you enter the workplace that you will work safely that day Part of
having a safe work attitude involves choosing to wear proper work attire Wearing
protective clothing or gear can prevent an injury or make an injury less severe
When working with power tools, for instance, it is important to protect eyes from flying
debris and ears from deafening noises If goggles and earplugs are not used, eyesight or
hearing could be damaged permanently
Work Clothes
Long trousers and sleeves help protect the arms and legs from cuts, scratches, and
other hazards Avoid wearing excessively loose or baggy clothing because it might
catch on a protruding object or get caught in power tools
Wear shoes that are appropriate for the job Sturdy, fully enclosed shoes should be
worn They should be able to protect the soles of the feet from sharp objects on the
floor Thick-soled shoes are best when working around nails, scrap metal, and other
materials that could puncture the soles of regular athletic shoes Steel-toed shoes can
protect toes when a heavy object is dropped on the shoes Also make sure that the
soles have traction, to prevent slipping
Eye Protection
Eyes are much easier to protect than to repair, so safety glasses should be worn when
cutting, drilling, sawing, or working in a crawl space (see Figure A-17) With some
cable-termination processes, as materials are cut, prepped, and discarded, there are
opportunities for small particles to become airborne While working with fiber optics,
the glass fibers, adhesives, and solvents can come in contact with the eyes Also, small
particles or chemicals might get on the hands and accidentally be rubbed into the eyes
Therefore, glasses also protect the eyes from contaminated hands It is a good idea to
wear safety glasses any time when working in a crawl space or above a dropped ceiling
If something falls from above, the eyes will be protected Many job sites require safety
glasses at all times
Trang 6Figure A-17 Eye Protection
Eye protection should be worn in all labs Before starting any lab exercise, review the safety instructions and safety equipment needed
Hard Hat Use
As with all safety equipment, a hard hat protects the user from injury Hard hats might
be required at job sites, especially those involving construction Many employers sup-ply hard hats; others require installers to buy their own The furnished hard hats might
be of a company color or might be equipped with company logos to identify the wearer
as belonging to a certain organization Even if you are purchasing a hard hat for per-sonal use, do not adorn it without obtaining permission from the employer In addi-tion, OSHA does not allow stickers on hard hats because they could hide cracks Periodically check the hard hat for cracks A cracked hat might fail to protect a head For hard hats to provide effective protection, they must be adjusted properly Take the time to adjust the internal straps to make sure that they function and ensure that the hat fits snugly and is comfortable Hard hats are required when working on top of a ladder and often are required when working in new-construction environments
Tools of the Trade
As with any craft, tools of the trade are often what makes the difference between a hard job with mediocre results and a simple job with outstanding results Students should get hands-on experience with several of the tools used by low-voltage cabling installers to have professional results
Students should become versed in the following technologies:
■ Stripping and cutting tools
■ Termination tools
Trang 7■ Diagnostic tools
■ Installation support tools
Stripping and Cutting Tools
Stripping tools are used to cut the cable jacket and insulation of the wires The Panduit
UTP cable-stripping tool (see Figure A-18) is used to remove the outer jacket from
four-pair cables It also can be used for most coaxial cable The tool features an
adjust-able cutting blade to accommodate cadjust-ables with different jacket thicknesses The cadjust-able
is inserted into the tool, and then the tool is twisted around the cable The blade cuts
through the outer jacket only, allowing the installer to simply pull the jacket off the
cable to expose the twisted pairs
Figure A-18 Panduit UTP Cable-Stripping Tool
The electrician’s scissors and cable knife set (see Figure A-19) also can be used for
removing cable jackets The knife is used for removing the jacket from large cables,
such as those that enter the building from the telco or ISP This knife is sharp, so care
should be taken when using this tool It is recommended that gloves be worn when
working with it, preferably gloves that will resist injuring the hand if the knife slips
The scissors can be used to cut individual wires, remove the outer jacket of smaller
cables, and remove the insulation on individual wires Not visible in the figure, the
scissors features two different-size notches on the back of the blade that will strip
insulation on wire sizes from 22- to 26-gauge
Trang 8Figure A-19 Electrician’s Scissors and Cable Knife
Termination Tools
Termination tools are designed to cut and terminate specific types of cable The multi-pair termination tool (see Figure A-20) is designed to terminate and cut UTP cable and seat connecting blocks This tool features an ergonomically designed handle that helps reduce fatigue when trimming wire or seating connecting blocks to the wiring base Additionally, it has the following features:
■ Terminates five pairs at a time
■ Terminates wires on both the cable side and the cross-connect side of connecting blocks
■ Has replacement cutting blades available
■ Can be used in the cut or noncut position
■ Clearly displays CUT designation for proper orientation during termination
■ Includes a reliable impact mechanism
■ Has an ergonomically designed rubber handle with a ribbed edge that provides
a no-slip grip The impact punchdown tool (see Figure A-21) has interchangeable blades so that it can terminate wires on 66 and 110 hardware Unlike the multipair termination tool, this tool terminates only one wire at a time The reversible blades have a punch-and-cut function on one side and a punch-only function on the other
Trang 9Figure A-20 Panduit Multipair Impact Tool
Figure A-21 Panduit Impact Tool
Diagnostic Tools
It is sometimes necessary to access individual wires inside a telecommunications outlet
or jack The modular adapter, or banjo, is used to provide access to these wires (see
Figure A-22) A common line cord is plugged into the adapters and then into the jack
The technician can use an ohmmeter or other test devices without having to disassemble
the jack Banjos come in three-pair and four-pair configurations
Lab Activity Tool Usage and Safety
In this lab, you learn to identify, examine, and use the tools that are used in cable installations
Trang 10Figure A-22 Modular Adapter (Banjo)
To locate metal pipes, wood studs or joists, or other hidden infrastructure behind a wall or under a floor, use wood and metal sensors This should be done before drilling for any cabling project A deep-scanning metal sensor can find metal studs, conduit, copper piping, electrical lines, rebar, telephone lines, cable lines, nails, and other metal objects This tool usually can scan through up to 15 cm (about 6 in.) of a nonmetallic surface, such as concrete, stucco, wood, or vinyl siding It identifies both the location and the depth of piping or rebar with an accuracy of about 30 cm (about 12 in.) Another type of sensor is a stud sensor (see Figure A-23) This sensor locates wooden studs and joists behind walls This tool helps the installer make informed decisions
on the best location to drill or saw when installing outlets or raceways The stud and rebar sensor also detects metal and even can find rebar embedded in up to 100 cm of concrete All the modes detect AC wires to alert the installer, to prevent drilling or nail-ing into a live electrical wire
Figure A-23 Stud Sensor