Power
= Voltage x Current = I2R
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Lightning—This
is the most catastrophic cause of voltage surges which can damage
a communications system. The building does not have to take
a direct hit for lightning to damage a system. A lightning strike
within a few miles can induce (described below) a surge which
can travel along aerial or buried cables into the equipment.
Lightning is both region and seasonal in nature throughout
the world. In the United States, for example, lightning season
generally runs from May through September. It is also geographic
in nature, with many of the most intense lightning storms coming
from the Southeast Coastal and Gulf Coast states. The chart
below shows lightning density over a nine year period in the
U.S.
While the lightning trends towards the Southeast,
it occurs throughout the country during lightning season.
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Power Line Crosses—When
the telecommunication line comes into contact with an electric
power line, it creates an excess current on the communications
line. This can be caused by an electrician accidentally crossing
a power line with a telephone line or a downed electric and telephone
line crossing. AC current is introduced into the phone line, which
normally operates on DC current. Often a power cross produces
very high voltage and current in the phone line and can last a
long time. For this reason, a power cross presents a high risk
of fire. If a protector does not protect the telephone circuit,
this energy can travel through the telephone circuit causing damage
to equipment and possible injury to personnel. |
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Induction—When
current flows through a conductor, such as a wire, a magnetic
field is created around the conductor – a basic principle
of physics. Alternating current (AC) creates a magnetic field
that has variable strength, continuously increasing and decreasing
in strength with the flow of current. If two conductors run parallel
and close to one another, the field of one conductor can transfer
energy to the other conductor, thereby making an electrical connection
without actually making a physical connection between the two
conductors. This transfer of energy is known as induction. For
instance, when the power cable experiences a large current demand,
such as occurs when power is first restored to service following
a power blackout, an AC surge can be induced into the phone line. |
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Electrostatic Discharge—Electrostatic
Discharge is the transfer of electrical energy from one material
to another material, through a conductive path to ground. Such
surges produce high voltage with low current. The problem is usually
found in dry climates, but also may be caused by the electrical
field that surrounds a high voltage power facility. For example,
when a person walks on a synthetic floor in a dry environment,
they commonly build up a static charge of 50kV in their body.
When they contact another material, this charge typically arcs
over to the contacted material. The discharge can be as high as
10 amps. This is enough energy to damage integrated circuits used
in telecommunications equipment. |
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Voltage and current can also be related through Ohm's
Law: Voltage = Current x Resistance
= IR
So what are the different types
of protection types for overvoltage?
Two technologies have won out over all others in the arrestor
arena: gas tubes and solid-state devices. Gas tubes are ideal to protecting
against high-energy surges. Solid-state arrestors are superior in
speed, voltage control, and long life. Each of these technologies
has appropriate applications in protecting today’s telecommunications
network.
Gas Tube—A
gas tube device consists of a discharge gap between two metal electrodes
sealed in a ceramic or glass envelope containing an inert gas or combination
of gases at low pressure. When the gas tube is subjected to a surge
voltage exceeding its static breakdown voltage, the gas ionizes and
forms a conducting path across the discharge gap. Because the gas
takes some time (a couple of microseconds) to ionize before discharging,
gas tubes have poor control of the peak voltage during a fast rate
of rise voltage surge. Once ionized, the ground path is sustained
at a voltage considerably lower than the static breakdown voltage.
The gas tube returns to its nonconductive state when the over voltage
and over current conditions are removed.
Though well suited for line surge suppression, gas tubes
by themselves generally have protective clamping voltages and discharge
times that are too high, too imprecise, and too slow (4,000 to 5,000
nanoseconds) to provide precision protection for solid-state equipment,
for example private branch exchange (PBX) or central office (CO) line
cards. Solid-state devices best protect such equipment. Similarly,
gas tube protection is inappropriate for lines that are susceptible
to frequent surges. Deposits build on the discharge plates with each
activating surge. Each discharge narrows the gap between the plates.
Solid State—Solid-state
devices provide fast, precise, and long lasting protection. These
protectors provide a premium alternative to gas tube protectors for
central office, building entrance, and other applications. Fast clamping
(2 to 5 nanoseconds) at low voltages as well as stable, quiet, and
truly balanced electronic solid-state performance can significantly
reduce failure rates for both protector units and surge sensitive
equipment. Improved protector reliability makes solid-state protectors
ideal for critical service lines.
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What is the main technology
difference between gas tube and solid-state?
The main technology difference between gas tube and solid-state
devices is the reaction time. Let’s review the speed of electricity
and compare it to the response time of commonly used protector components.
In its ideal state, electricity travels at the speed of light or one
foot every nanosecond (billionth of a second). Gas tubes take 4,000
to 5,000 nanoseconds to react due to the time it takes to ionize the
gas within them. This equates to the surge traveling roughly 1 mile
down the line. The equipment is still vulnerable at this point. The
solid-state device reacts as quickly as electricity can travel. Solid-state
protectors limit the distance the surge can travel to within two to
five feet. Solid-state protectors are the fastest technology available.
So, why are the other protectors used? Well, gas-tubes are the traditional
protectors that were used by the Telephone companies to provide people/structure
protection. However, it has become obvious that the faster, solid-state
protectors are required to protect sensitive semiconductor based equipment.
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So what are the different types
of protection types for overcurrent?
Overcurrent protection, which reduces the likelihood of fires
caused by power line crosses, is required under NEC for equipment
connected to telecom networks and for campus environments. Modern
telecom equipment, with its sensitive, solid-state componentry, needs
overcurrent protection to protect people and equipment.
Fuses—Fuses
prevent fires. If an overcurrent situation develops, the fuse will
open the circuit, removing the load from the equipment and eliminating
the possibility of a heat-induced fire. Therefore, finding the line
fault is as easy as replacing the fuse at the terminal block since
the fuse opens prior to the equipment or cable. All lines that enter
a building require some type of overcurrent protection. The primary
overvoltage system installed by a telephone company typically uses
a thermally-activated, fail-safe mechanism that shorts to ground if
an overcurrent fault situation develops. In addition, the telco installs
a wire fuse link to work with the fail-safe mechanism. The wire fuse
link, which often is built into the primary protector block base at
the building entrance, opens the circuit by melting – but it
won’t open until the fail-safe mechanism shorts to ground. Therefore,
there must be enough heat buildup in the fail-safe mechanism to make
it short to ground before the wire fuse link functions as a “fuse”.
If the power cross voltage is less than the firing voltage of the
primary protector, overcurrent in the building wiring may result.
Without sneak current protector fuses, this overcurrent may cause
a fire. Open wire fuse links, especially in the primary protector
block base, require visual/manual inspection to determine which wire
has shorted. For example, consider that there are two wire fuse links
for every trunk line entering the premises. Locating the open wire
in a bundle of wires is time consuming, expensive, and potentially
dangerous if the power cross remains on the line. A fuse eliminates
this potential for injury to the repair person because a blown fuse
is easy to test and identify. First, primary or secondary protection
is in an easily identified, controlled location. Second, individual
fuses are packaged in electrically insulated housings. Third, the
fuses can be easily checked for continuity at the block terminals
or contact points. After the cause of the problem has been identified
and corrected, the blown fuse is replaced. Wire fuse links are relatively
insensitive when compared to the current limiting needs of most electronic
equipment. Fuses offer a broader range of sensitivity and greater
control of the fault current or power cross event.
PTC Fuse—A
Positive Temperature Coefficient (PTC) fuse is an overcurrent
protection device that trips when a certain trip current is exceeded.
In contrast with conventional fuses that need to be replaced, resettable
PTC fuses automatically reset once the overcurrent is removed. A current
flowing through the device generates heat. If the current increases
enough, the corresponding temperature rise causes a dramatic increase
in resistance. Current flow is reduced accordingly and the fuse will
stay open until power is removed. The convenience of self-resetting
opens many application areas where conventional fuses are impractical.
Service calls are dramatically reduced due to the self resetting capabilities
of PTC fuses.
Heat Coil—A
low-cost overcurrent protector that the regulated telephone company
typically provides in the primary overvoltage device as a failsafe
mechanism. If an overcurrent condition develops, the heat coil shorts
to ground. But if excess current remains on the line, a fire might
result. To eliminate that possibility, the telco also installs a bridle
wire, often built into the primary protector system at the building
entrance that works as a fuse link. If the heat coil shorts to ground
and the power cross continues, the bridle wire opens the circuit by
melting. The problem with this setup is repairs. If bridle wires are
on the primary protector block base, finding the shorted wire(s) is
like looking for a needle in a haystack, especially in commercial
installations. And if overvoltage remains on the line there is the
threat of a dangerous shock as the repairman pokes around, looking
for the short.
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What are some of the standards that should be known?
There are a number of standards out there that should be known
when discussing telecommunications. With respect to protection products,
the main standards to keep in mind are: the National Electric Code
(NEC) Article 800, Underwriter’s Laboratories (UL), and Telecommunications
Industry Association (TIA). The codes are as follows:
• National Electric
Code – Article 800: National Electric Code
Article 800 states two main points. First, it states that all conductive
paths entering or leaving a building shall be protected by a listed
primary protector as soon as possible, but no more than 50 feet past
the building entrance. Secondly, it does not state that you must have
secondary protection, but if you do have it, it must be listed for
that purpose (i.e. UL 497A).
• Underwriter’s
Laboratories (UL): Many of the UL tests are developed
as catastrophic tests with the goal of stressing the product beyond
normal operating parameters. A product that is listed for the purpose
of a specification has proven that when tested per the specification:
it
does not start on fire or cause a fire to be started,
and it does not
cause a physical safety hazard to the user.
Listed products are not necessarily required to function
after the tests, but are required to be safe or ‘fail safely’.
These activities are done to assure the validity of the product listing
and are required in order for a product to carry the UL listing label.
• UL 497—Primary
Protectors: According to NEC, primary protection
systems must be listed for the purpose and located as close as possible
to the building entry point on exposed telephone circuit. Exposed
circuits are telephone company cables that enter the building from
the outside world. The listing requirement is UL 497 for all primary
protection systems (Figure1, points A and D).
• UL 497A—Secondary
Protectors: A secondary protection system must
be listed for and be installed in series between the primary protector
and the protected equipment. All secondary protector systems must
safely limit overcurrents to less than the current carrying capacity
of the telephone cables and equipment. The listing requirement is
UL 497A for all secondary protection systems (Figure 1, points B and
C).
• UL 497B—Isolated
Loop Protectors: This requirement covers protectors
for isolated loops or lines that are contained within a building and
not connected to the public network outside the building. These devices
protect against transients usually caused by electrostatic discharge
and electrical shock.
Protectors are Listed for their purpose and must be
deployed per the official UL/Manufacturer installation instruction.
Each specification applies to one of three possible protection locations.
The specifications are not interchangeable.
• Telecommunications
Industry Association (TIA): The TIA provides
guidelines for installations and standards for performance of telecommunications
systems. From a data transmission viewpoint, TIA uses categories to
describe the performance (Category 3, 4, 5, 5e, 6, 7).
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Where are the Primary, Secondary and Isolated Loop
applications located?
PRIMARY (UL 497)—UL
497 calls for building entrance protection wherever cabling enters
or leaves a building. At building entrance, the telephone company
provides the protection (TELCO DEMARCATION POINT- Figure 1, Point
A). Typically, this protection consists of a five-pin gas tube module.
They provide this protection in order to meet NEC Article 800 which
calls for protection against fire within the building and against
personal injury within the building. Gas-tube modules, however, are
not adequate enough in order to protect today’s sensitive electronic
equipment.
Primary protection must be installed within 50 feet
of the building entrance point on any “exposed” communications
line that enters the building from outside, including exposed customer
premises lines connected between buildings (Figure 1, point D). The
primary overvoltage device installed by the telco at the network interface
(point A) is typically rated from 350V to 600V. This device, however,
is designed to protect people and the public network cables—not
sensitive electronic components.
People can safely handle a quick 5000V-to-10,000V shock
characteristic of static electricity. However, solid-state circuitry
can be damaged in microseconds by a transient voltage surge as low
as 100V. Fast-response primary protection should be used on those
customer premises lines that are exposed to lightning; for example,
in a campus environment.
SECONDARY (UL 497A)—Secondary
protection is by definition, the protection placed between the primary
protection and the equipment meant to be protected (Figure 1, Points
B & C). It is additional protection that is meant to stop any
surges that the Primary protection was not able to protect against.
The other reason for secondary protection is to protect against any
events that might occur between the primary protection and the equipment,
which occurs quite often. Any conductive path leading into the equipment
is a potential threat for a surge. Therefore, it is wise to provide
this secondary protection within close proximity of the equipment
intended to be protected.
Secondary protection must be installed at point B or
C by an interconnect or by other installers to ensure that protection
for the equipment conforms to UL 1459 and UL 497A listing requirements,
and the manufacturers’ installation instructions. Secondary
protection devices consist of either sneak current protectors, or
both sneak current protectors and solid-state voltage suppressors.
Sneak current protector fuses limit current to
350 milliamps to protect equipment and cables from fire hazards. The
solid-state suppressor responds within billionths of a second (nanoseconds)
and clamps overvoltage to ground. Clamping voltage ratings range from
5 volts to 400 volts, thus offering protection for telecommunications
equipment that uses very low operating voltages.
In combination devices, the integral sneak current protectors
should be easily replaceable.
OFF-PREMISE EXTENSIONS—An
off-premise extension line permits a telephone not at a company’s
location to function to all intents and purposes as though it is located
at the company’s location. This capability becomes particularly
interesting with the recent increase in telecommuting. With an off-premise
extension (using copper), you are creating another path for which
a surge can enter into the equipment. According to NEC Article 800,
you would need primary protectors at both building entrances. Secondary
protection provides the same benefit in the main building on the off-premise
side of the equipment as does the CO side of the equipment. Expensive
phone sets can be protected from damage in this situation also with
the use of station protection.
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What is the best way to describe protection equipment
in Telecommunications?
Telephone access is provided by your local provider from the Central
Office. The cable is taken to the individual building and is cut of
at the Telco Demarcation point. At this point, the telephone company
provides primary protection. They do so because they have to meet
code—NEC Article 800 states that you must have a list primary
protector on all lines at the building entrance and no more than 50
feet (and they are responsible for that). They are not concerned about
the equipment within the building, but rather to meet code to save
themselves from lawsuit or any other problems. With that being said,
they commonly use a gas tube five pin protector as the protection
for Telco demarcation. This brings us to the first critical aspect
of surge protection—the technology type used (see “Gas
Tube vs Solid-State”).
This topic is a hot topic due to the technology differences
in today’s world. Back when telephone systems were actually
electro-mechanical switches, they could handle severe surges and not
have any damage done. The gas tube simply took the surge off the line
and nobody was hurt. Over the past 20 years or so, however, the technology
has become increasingly complex and sensitive, so the protection is
more expensive as well. Where the gas tubes were able to protect electro-mechanical
switches, the newer equipment needed a better technology to stay protected—then
there came the Solid-state device. The main difference between the
gas tube and solid-state devices is the time it takes to remove a
surge off of the line. They both do so by diverting the surge to ground,
but the gas tube does it in 4,000 to 5,000 billionths of a second
(nanoseconds), and the solid-state devices do it in 2 to 5 nanoseconds.
These times equate to distances the surge travels with the relationship
that one nanosecond equals one foot down the cable. Therefore, gas
tube protectors allow the surge to travel approximately 1 mile down
the path, whereas solid-state cuts the surge in nearly no distance
at all. So why do people still use gas tube protectors? Simple—money.
When it comes down to it, even those who are educated on the differences,
they still go with gas tube because it is cheaper. Well, there are
some consequences to this. First off, you can easily lose equipment
with a damaging surge on the line. Secondly, even if the surge isn’t
catastrophic, they can still degrade the system over time—until
one day it doesn’t work at all.
Data Surge Protection
Solid-state protection devices are designed to react in 2-5 nanoseconds.
Recalling our previous calculation, for each nanosecond that passes,
the surge travels one foot down the cable, we can see that the solid-state
device will clamp the surge to ground within 2-5 feet of the protector.
Thus, the network equipment never sees this energy and the network
administrator sleeps at night. ITW Linx protection products use 100%
Solid-State protection to ensure your equipment doesn’t see
the intense energy of a lighting surge. But wait—there’s
more! Solid-state surge protection solves the surge speed problem
but what about the effects of introducing additional electronic components
in the network. If you aren’t careful, a protection device that
is not designed for high speed networks such as: xDSL, ISDN, T-1,
10BaseT, 100BaseT and even 1000BaseT, will introduce errors in the
transmission and cost network efficiency and performance.
The ITW Linx series of Category 5e/6 Building Entrance
Protectors are the right choice for your application. They are designed
to provide nanosecond response to surges via Solid-state Technology.
They meet UL497(Primary Protection) requirements for Building Entrance
Protection. And they use patented Technology to ensure transparent
protection performance in 10/100/1000BaseT networks. Contact ITW Linx
for more information on Premise Network Protection Products.
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Why ITW Linx protection?
• How costly and aggravating down
time is for business damaged equipment
= down time = lost revenue = customers left unsatisfied
• How much business
would you lose if your system went down for 10 minutes? An hour? A
day? Permanently?
• Is it worth a
few extra dollars per line to ensure the continued operation of your
voice and data system for the most robust self-setting technology
available? ITW Linx custom protection systems are cost-effective because
they can be applied selectively, to only those lines that need protection
and can be added incrementally.
Who Benefits, and How?
Everyone benefits in the end, and here’s how:
Distributors—By
providing the highest quality product at the lowest possible cost,
you gain customers that achieve a higher level of satisfaction. With
proper protection in Linx products, the customers will not experience
down time, lose money, or business. In the end, it is a win-win situation
for the distributor and the end user who gets what they paid for.
Your customers will also keep coming back if you can maintain this
level of satisfaction.
Interconnects—Keep
bids low by using cost effective protection devices with value added
features. By knowing the codes and technology types, you are one step
in front of the next guy. Linx protection products use nothing but
the best technology—solid-state. With the best possible technology
at the lowest affordable price, you can’t go wrong.
Equipment Owner—Keep
your equipment protected, your building safe, and your personnel free
from danger. With Linx protection, downtime and damaged equipment
will be a thing of the past. Don’t worry about expensive replacement
costs of labor or equipment. Make sure you are to code (NEC Article
800).
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