5044 B U Bowman Dr #102  :::  Buford, Georgia  30518

e-mail stedipower@tvss.net   :::  Phone: 678.546.6780

Overview: Why should you consider Voice and Data Surge Arresters and Suppressors?

    Many telecommunications system problems are voltage- and/or current-related. High voltage surges, often caused by lightning, can damage or destroy sensitive telecommunications equipment while high current can cause building fires. Line cards cost hundreds or thousands of dollars to replace, yet most customers think their new telephone systems shouldn’t break down and don’t want to pay for repairs.

Safety
    The safety goals are to protect people from electric shock, protect equipment from damage, and protect building wiring from excessive electrical current. Providing surge protection minimizes, as far as practical, electrical hazards to persons engaged in the operation, maintenance, and use of telecommunications systems.

National Electric Code (NEC) Article 800
    The National Electric Code (NEC) Article 800 calls out telecommunications codes. It calls for primary protection at the building entrance. The NEC also states that if secondary protection is used, it must be listed for that purpose.

Investment protection
    As with any big investment, you want to protect that investment with some sort of insurance. Surge protection on the telecommunications lines is that insurance you are looking for. Looking at the cost to protect the equipment versus the cost of losing the equipment to a potential surge, it is clear that surge protection should be installed on every possible path entering or leaving the equipment.

Business Downtime = Lost Revenue
    Not only does loosing the equipment have economic importance, but the down time associated with the lost equipment can be even more costly. Downtime of the equipment equals thousands of dollars in lost revenue for companies – not to mention their upset customers.

Service Savings
    With solid-state protection, the protectors are self resetting, eliminating the need for service calls on your telecommunications line. PTC fuses are also resettable to also reduce service calls while providing overcurrent protection.

Responsibility
    The question of who is responsible for providing primary and secondary protection is often misunderstood.  The regulated telephone company is only responsible for providing a standard level of primary over-voltage protection for central office trunks connected to the customer premises at the network interface.

    All the other customer premises protection is the responsibility of the installing interconnect and the equipment owner.

What is the nature of the threat?
    The threat to the communications equipment consists of over-voltage, over-current, or both. The over-voltage element can destroy semiconductors in the PBX, KSU or CPU; while over currents c an generate enough heat to cause a building wiring fire. 

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.

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.

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 pow er blackout, an AC surge can be induced into the phone line.

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 (50,000 Volts) 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.

Technology Comparisons of Over-Voltage Protective Devices
    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.

Technology differences 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 t ake 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.

Types of Over-Current Protection
    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 d evelops, 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. If overvoltage remains on the line there is the threat of a dangerous shock as the repairman pokes around, looking for the short.

STANDARDS
    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 o perating 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.

• 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

• 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.

• Telecommunications Industry Association (TIA)
    The TIA provides guidelines for installations and standards for performance of telecommunications systems.& nbsp; From a data transmission viewpoint, TIA uses categories to describe the performance (Category 3, 4, 5, 5e, 6, 7).

PRIMARY PROTECTORS (UL497)
    UL 497 calls for building entrance protection wherever cabling enters or leaves a building. At building entrance, the telephone company provides the protection . 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 . The primary overvoltage device installed by the telco at the network interface 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 PROTECTORS (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 prot ect 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 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 over-voltage 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.

TELEPHONE COMPANY SUPPLIED PROTECTION?

    Telephone access is provided by your local provider fro m the Central Office. The cable is taken to the individual building and is cut off 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.  The most commonly used device is the gas tube five pin protector as the protection for Telco demarcation.  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.  

    The main difference between the gas tube and solid-state devices is the time it takes to react to a surge. Both devices 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. 

Data Surge Protection Considerations

     Adding solid-state components to your system could create complications, though.  Without proper precaution, a protection device that is not designed for high speed networks such as DSL, ISDN, T-1, 10BaseT, 100BaseT and even 1000BaseT network s will introduce errors in the transmission and cost network efficiency and performance.

    Stedi-Power only sources equipment fully qualified to handle the most demanding data applications.

    For more information about Category 5 systems, go:

Stedi-Power, Inc
5044 B U Bowman Drive #102
Buford, Georgia 30518
PHONE: (678) 546-6780

Last Updated: 07 Jun 2004
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