TIA TSB-153-2003 Static Discharge Between LAN and Data Terminal Equipment《LAN和数据终端设备之间的静电放电》.pdf

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1、 TIA TELECOMMUNICATIONS SYSTEMS BULLETIN Static Discharge Between LAN and Data Terminal Equipment TSB-153 NOVEMBER, 2003 TELECOMMUNICATIONS INDUSTRY ASSOCIATION The Telecommunications Industry Association represents the communications sector of NOTICE TIA Engineering Standards and Publications are d

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9、t No. 3-0127, formulated under the cognizance of the TIA TR-42.1 Subcommittee on Commercial Building Telecommunications Cabling. . Published by TELECOMMUNICATIONS INDUSTRY ASSOCIATION 2003 Standards and Technology Department 2500 Wilson Boulevard Arlington, VA 22201 U.S.A. PRICE: Please refer to cur

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24、abling and Data Terminal Equipment Contents FOREWORD . II 1 INTRODUCTION. 1 2 PURPOSE AND SCOPE 1 3 REFERENCES 1 4 DEFINITIONS, ACRONYMS, & ABBREVIATIONS. 1 4.1 Definitions . 1 4.2 Acronyms and abbreviations. 1 5 WHAT IS STATIC DISCHARGE? 1 6 HOW DOES ESD AFFECT TELECOMMUNICATIONS CABLING AND EQUIPM

25、ENT? . 1 7 WHAT PRECAUTIONS ARE NECESSARY TO AVOID EQUIPMENT DAMAGE? 2 8 ARE CATEGORY 6 CABLES WORSE THAN CATEGORY 5 CABLES FOR ESD EFFECTS? 2 9 CABLING GUIDELINES FOR ESD 5 List of Figures Figure 1: Charging Point. 3 Figure 2: Cable Layout 3 Figure 3: Discharging Point 4 Figure 4: Discharge wavefor

26、ms for t=4 hours time interval (with unused pairs floating) after correction for humidity. 4 FOREWORD (This foreword is not part of the Standard) TIA standards documents are developed within the Technical Committees of the TIA and the standards coordinating committees of the TIA standards board. Mem

27、bers of the committees serve voluntarily and without commission. The companies that they represent are not necessarily members of the TIA. The standards developed within the TIA represent a consensus of the broad expertise on the subject. This expertise comes from within the TIA as well as those out

28、side of the TIA that have an expressed interest. The viewpoint expressed at the time that this standard was approved was from the contributors experience and the state of the art at that time. Users are encouraged to verify that they have the latest revision of the standard. This TSB has been prepar

29、ed and approved by the TR-42.1 Subcommittee. 1 1 INTRODUCTION Electrostatic discharge (ESD) is a natural phenomenon where electrical charges that build up over time suddenly discharge into networking equipment, or other objects with possible detrimental effects. 2 PURPOSE AND SCOPE This TSB includes

30、 background information on ESD properties of different cable categories and provides installation guidelines to mitigate electrostatic discharge effects in balanced twisted pair cabling systems. 3 REFERENCES IEC/EN 61000-4-2: Electromagnetic Compatibility (EMC) Part 4-2: Testing and Measurement Tech

31、niques-Electrostatic Discharge Immunity Test, 1995 4 DEFINITIONS, ACRONYMS, & ABBREVIATIONS 4.1 Definitions None 4.2 Acronyms and abbreviations ESD Electrostatic discharge 5 WHAT IS STATIC DISCHARGE? Electrostatic charges are generated when different materials come into contact and are then separate

32、d. When materials come into contact, a chemical bond of varying strength is formed between the two materials. The chemical bond involves a migration of electrons from one material to the other. When this bond is broken, some of the electrons may be left behind resulting in an excess negative or exce

33、ss positive charge on the materials. This charging effect caused by contact is made even greater by friction such as rubbing the two materials together. This phenomenon is called “triboelectric effect,” or “triboelectric charging.” The amount of charge that is generated can be significant, in many c

34、ases tens of thousands of volts. The amount of charge, and hence the voltage that can be supported by a material, is governed by its bulk resistance or insulation properties. A capacitor is a device designed to store charge that has a good insulator sandwiched between two good conductors. The charge

35、 is stored in the insulator. A good conducting path will allow this stored charge to dissipate rapidly. “Rapidly” is the key word because this quick discharge of large amounts of potential energy can cause damage. This is called electrostatic discharge, or ESD. A slow or controlled discharge is one

36、of the more useful ESD protection strategies. 6 HOW DOES ESD AFFECT TELECOMMUNICATIONS CABLING AND EQUIPMENT? Any users (installers, administrators, end users, etc.) that touch equipment or cabling become a potential source of ESD into communications equipment. For example, a person can become charg

37、ed by triboelectric effect by walking across a carpeted floor. The international standard IEC/EN 61000-4-2 specifies test levels and procedures for manufacturers to verify equipment immunity to discharge from a human body. It also includes specifications for the installation and handling of equipmen

38、t. Another subtler source of ESD is from charged cabling. The IEEE 802.3 standards identify this problem, but do not provide any guidance or testing methods for manufacturers. Generally, users become a source of ESD to the cabling and the charged cabling then becomes a source of ESD to the communica

39、tions equipment. Cables can acquire a charge during installation when they are unreeled from a cable reel, or dragged across a floor. There have also been reports of cables developing their own charge from moving air or from building occupants walking over floor ducts. If the cables are not connecte

40、d to earth ground, the electrostatic charges can remain for a long time, especially in dry conditions. 7 WHAT PRECAUTIONS ARE NECESSARY TO AVOID EQUIPMENT DAMAGE? The IEEE has warned about the effects of ESD on equipment by incorporating guidelines in 802.3i-1990 Twisted-Pair MAU and Baseband Medium

41、, Type 10BASE-T since 1990. The same guidelines continue to be incorporated in subsequent applications, including 802.3u-1995 Type 100BASE-T, 802.3x-1997, 802.3y-1997 (100BASE-T2), 802.3ab-1999, Type 1000BASE-T). The following is from section 14.7.2 of the 10BASE-T document: “14.7.2 Network Safety:

42、(2) Static charge buildup on LAN cables and components. Such electrical safety hazards must be avoided or appropriately protected against for proper network installation and performance. In addition to provisions for proper handling of these conditions in an operational system, special measures must

43、 be taken to ensure that the intended safety features are not negated during installation of a new network or during modification or maintenance of an existing network.” Although these guidelines are written for the manufacturer, the intent is that they be incorporated into the manufacturers product

44、 documentation as well. With properly designed equipment, and good installation practices, the numbers of ESD problems that have been reported over the last 10 years have been very limited. 8 ARE CATEGORY 6 CABLES WORSE THAN CATEGORY 5 CABLES FOR ESD EFFECTS? A cables capacitance to ground determine

45、s how much charge a cable will hold. Once a cable is charged, its capacitance to ground and the relative humidity typically determine how fast the charge will dissipate. Generally, dielectric materials and the capacitances associated with category 5e and category 6 cable designs are the same as thos

46、e associated with category 5 cables. Hence, the ESD discharge properties of these cables are not significantly different. This was confirmed by laboratory measurements of discharge patterns as outlined in the following experiment. A Human Body Model ESD generator, of the kind described in IEC 61000-

47、4-2, was used to inject an 8KV contact-discharge pulse into one end of a conductor pair of an assortment of category 5 and category 6 UTP cables, each about 56 meters in length. After charging, a cable discharge waveform was then measured into a high-speed waveform recorder. These discharges were re

48、corded as a function of the time interval between the charging and the discharging of the conductor pair so that a charge retention profile was also recorded for each cable. To ensure repeatability and a fair comparison, each cable was laid directly on a ground plane for its entire length. This also

49、 maximizes its capacitance to ground (See figure 1, figure 2 and figure 3). 3 Figure 1: Charging Point Figure 2: Cable Layout Figure 3: Discharging Point What was found? It was readily apparent that the humidity level was a very important factor in the charge retention properties for all of the cables tested. After correcting for the effects of changes in the relative humidity, a comparison of these time-dependent discharge profiles shows very little difference in the charge retention and discharge properties of different category 5e and category 6 cables. 0123456789100 50 10