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Network Cabling Systems Power Protection, Grounding and Bonding Updated Jan 2014 ©[email protected] 1 Ground A Ground is ‘a conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth.’ image: wiki ◦ NEC Article 100 The earth is considered electrically neutral (does not carry either a positive or negative charge). 2 Bonding Bonding is ‘the permanent joining of metallic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct any fault current that is likely to be imposed.’ image: www.navasola.com ◦ NEC Articles 100 and 250-70 3 REASONS FOR GROUNDING 4 Noise: Electromagnetic Induction Principle: ◦ Magnetic flux lines crossing a conductor will induce current. ◦ There must be relative motion. This is created by the alternating current of the source. Source Current Induced Current 5 Sources of Noise Ambient Noise: ◦ Background, steady, predictable noise. ◦ The most common source of ambient noise is the building’s electrical system Transient Noise: ◦ Irregular and unpredictable noise. ◦ Transient noise is often difficult to pinpoint. ◦ Likely sources are switching circuits when current draw changes abrupty 6 Noise The currents from power and communication cabling will induce current on all metallic and conductive elements in the vicinity including cable shields, computer chassis, cable trays, conduit, cabinets, racks and other support systems. The noise induced on these elements may eventually spread the effects of noise onto other communication devices and cables. Reason: Noise Control Connecting all conductive elements of the data communications infrastructure to an effective grounding system will conduct the induced current to earth ground and remove its potential for creating additional noise. 8 Static Electricity Static Electricity is an electrical charge that has accumulated on an object. Static electricity develops whenever objects move, including a person or a person’s clothes. ◦ Can easily exceed 10,000 Volts. Humans can feel about 3000 Volts. 9 Hazards of Static Electricity Equipment damage image: mult sources ◦ Static charges as low as 10V or less can permanently damage communication and electronic components and equipment Ignition ◦ Static discharges can ignite flammable liquids and gases. Other ◦ Static discharge through a person may cause involuntary movement and injury via secondary contact. ◦ Items may tend to stick together creating a nuisance. 10 Working with Static in Mind Ground yourself and your equipment (wrist straps and mats) ◦ Do not ground yourself when working near high voltage sources. Don’t let anyone touch you when working on circuit boards or other static sensitive items. Transport electronic components and cards in staticshielding bags Keep static-inducing non-conductors such as styrofoam away from electronics 11 Reason: Effective Static Control Use static control systems designed to connect to earth ground Connect the static control to an effective ground to neutralize the static charge image: support.sonus.net 12 Electrical Faults An electrical fault in an electrical cable or equipment may cause chassis or other conductive components to be energized, creating a significant hazard ◦ Electrical shock hazard to people touching the energized component ◦ Equipment damage ◦ Fire 13 Reason: Electrical Fault Control Two elements of a good electrical fault protection: ◦ An effective ground system that will safely conduct the electrical energy to earth ground and ◦ A fuse or breaker on the ‘hot’ side that will open the electrical circuit should there be a short circuit to ground 14 Lightning When lightning strikes it carries both a very high voltage and a large amount of current Lightning strikes are somewhat unpredictable Indirect lightning damage can occur when it follows a cable, fence or other conductive path image: blog post 15 Effect of lightning striking an underground cable. Note the sand has been turned to glass, known as fulgurite. images: plaza.ufl.edu 16 Reason: Lightning Control Ensure an adequate lightning control system in in place, including an independent and effective grounding connection Follow a safety plan than minimizes the exposure to a primary or secondary lightning strike Employ an effective building entrance protection for all metallic elements of the communication cabling 17 Effective Grounding 18 Establishing an Effective Ground The earth is a conductive body, and is considered electrically neutral (neither a positive nor a negative charge). Establishing an effective ground is important for safety and systems performance 19 Grounding Electrode System A grounding electrode is a metallic conductor (rod, pipe, plate, etc.) in contact with the earth The system may be a network of connected electrodes Its installation and use is defined in the Electrical Code Not the responsibility of a communications systems designer except when needed for communication-only applications. 20 Grounding Electrode Systems Normally consist of: ◦ Grounding electrode Rod, plate, pipe or other conductor that is in constant and lengthy contact with the ground ◦ Grounding wire Large gauge copper conductor, typically stranded, may not have a jacket, should be continuous ◦ Bonding devices A clamp or other means of attaching the grounding wire to the grounding electrodes and to the items that require grounding 21 Grounding Exterior Grounding Electrode System Ground Wire Building Ground Clamp Image: PRGodin Earth Grounding Electrode 22 Typical Ground in a House In this image 2 ground wires are attached via a grounding clamp to the metal water pipe Image: PRGodin 23 Typical Ground in a House This image demonstrates a ground wire clamped to a metal gas pipe. Image: PRGodin 24 image: www.electrical-contractor.net Exterior Gounding 25 Codes and Grounding Grounds are an important part of electrical safety and their installation is described in the electrical code. Each municipality may make its own rules regarding grounding. An independent grounding system may be required for lightning protection. This system should not be used for grounding data communications equipment. 26 Ground Types There are 3 basic types of grounds in communication 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 noise shielding. Meant to have a potential of 0 Volts. ◦ Common ground: a point of reference for signals and voltages within a circuit. A relative reference point for voltage, it’s often not connected to earth or chassis ground. Earth Ground Chassis Ground Common Ground 27 Effective Grounds Good earth connection ◦ Proper installation of the electrodes ◦ Good soil conditions Low resistance path ◦ Larger AWG of wire ◦ Good bonding connections Short path 28 Electrical Overview 29 Electrical Basics 3-wire system in North America ◦ Neutral is wider slot The neutral is connected to earth ground at the transformer Forms the return path for current Not safe as ground ◦ Hot wire is narrower slot The Hot is connected to the transformer Current and voltage source ◦ Ground is the round hole The Ground is connected to the building ground Must not carry current under normal conditions 30 Electrical Supply The electrical voltage used in N. America is 120VRMS This voltage may vary based on location and on overall system load: ◦ As low as 110V during peak hours (5PM-10PM) ◦ As high as 130V overnight Although electrical supply in N. America is fairly reliable some problems may occur 31 Blackouts Complete power outage Have multiple causes (from squirrels to auto accidents to power generation problems) Back-up Power Supplies and UPS’s are a solution What type of data communications-related damage could occur with blackouts? http://www.powerware.com/blackouttracker/default.asp?cx=5&CC=1 32 Brownouts and Surges Decreases or increases in voltage that can last a considerable amount of time Brownouts may occur in situations where too many power plans are off-line Back-up Power Supplies and UPS’s (Uninterruptable Power Supplies) are a potential solution What type of data communications-related damage could occur with brownouts or surges? 33 Spikes and Drops Last between 0.5 and 100 microseconds Amplitude of over 100% peak line voltage or a cycle completely missing Typically caused by EMPs from high load switching, electrical storms and utility switching Quality surge suppressors and UPS can offer protection 34 Harmonics Secondary signal on top of the regular waveform with a magnitude ranging from 15 to 100% of nominal line voltage Increases power supplied to load Caused by: ◦ Power transformers, motors and motor drives ◦ Non-linear loads (loads that vary in their current draw) such as power supplies and dimmers Dedicated circuits or UPS equipment will reduce harmonics 35 Reducing Electrical Problems Maintain isolated circuits for data communication equipment ◦ The symbol for an isolated ground is an orange triangle. Often the entire receptacle is orange ◦ Isolated grounds must be professionally installed ◦ Do not allow other appliances to connect to an open outlet Use good quality surge suppressors ◦ Surge suppressors often have a limited lifespan Use line filters Consider a UPS for critical systems ◦ Variety of options available Isolated Ground Symbol (Orange Color) 36 Electrical Safety image: http://www.nachi.org/forum/ 37 Safety A primary responsibility of the communication systems installer is safeguarding personnel, property and equipment from “foreign” electrical voltages and currents. Foreign refers to electrical voltages or currents that are not normally carried by, or expected in, the telecommunications distribution systems. 38 Safety The results of such disturbances could be: ◦ ◦ ◦ ◦ Death by injury. Destruction of electronic equipment. Down time. Work and/or process degradation. 39 Level of Electrical Shock Effects on the body are related to the duration and power of the shock, and the resistance and position of the body. The body can feel 1 milliamp of current and the muscles involuntarily contract with as little as 10-15 milliamps 100 to 200 milliamps (0.1 to 0.2 Amps) often fatal as it clamps the heart Over 200 milliamps causes physical injury Low level currents can cause injuries or death from involuntary muscle reflex reactions 40 Electrical Intrusion Frayed electrical cords, loose internal electrical connections or intrusion into electrical cables or systems may energize cases or chassis. Tools, chassis, racks, cabinets and any other conductive structure must be grounded. 41 Common Electrical Accidents The most common electric shock occurs from inadvertent, accidental contact with energized devices or circuits. Cutting or drilling blindly into a wall Unprotected or exposed electrical system on a construction site ◦ Panels, cables, outlets, switches, etc ◦ Faulty installation (exposed or unterminated live wires). Assuming a cable is not live Digging into an electrical cable Working too closely to overhead lines 42 Responsibilities Unless you are a certified electrician it is illegal for you to perform any work on electrical systems. Establish a relationship with a trusted electrician for those times when electrical work is required. Report all electrical workplace hazards. 43 Lightning Protection 44 Lightning Protection Planning Lightning is somewhat unpredictable. Careful planning is required to protect people, buildings and equipment from damage. Described in detail in ANSI/NFPA 780 TIA/EIA requires a lightning protection system, but this system is not the responsibility of the communications system designer 45 Basic Lightning Protection A zone of protection surrounds building to intercept, divert, and dissipate strikes A system of equalizing, air and ground conductors make up the building grounding system A Cone of Protection is an area under a nearby lightning protection system. image: Public Domain Cone of Protection 46 Lightning Protection Systems Provide a designed path for lightning current to travel Includes: ◦ ◦ ◦ ◦ Air terminals (lightning rods) Conductors Ground terminations (ground rods) Surge arresters and surge protectors The telecommunications ground must be bonded to the lightning protection system within 3.7 meters of the base of the building image: wiki 47 Buried Cable Planning Susceptibility is determined in part by soil resistance ◦ buried cable collects ground strikes within an area determined by soil resistance, typically 2-6 m (6-20 ft) ◦ high soil resistance intensifies this problem Recommendation is to provide a grounding system for all buried cable 48 Aerial Planning Aerial cables often have power cables above ◦ The power cable may intercept or divert lightning strikes ◦ This helps, but does not eliminate the need for protectors 49 Working Outdoors with Lightning Lightning claims more lives in Canada than hail, tornadoes, wind and rain combined. If working outdoors and a lightning storm is approaching, seek shelter in a passenger vehicle or protected building. Although there is a “Zone of Protection” under lightning attractors, lightning may travel through the ground and strike people. ◦ Avoid standing next to lightning attractors such as trees, lighting and other tall objects ◦ Metal fences, rail tracks, cables and other structures can carry strikes over large distances and into the “Zone of Protection” http://www.ccohs.ca/oshanswers/safety_haz/lightning.html 50 Protection & Electrical Code Lightning Exposure (Telecommunications) ◦ The CEC requires a listed primary protector (at both ends) whenever outside plant cable may be exposed to lightning or electrical power disturbances Telus Residential Installation Document, including Network Interface Devices (NID) (images: www.telus.com) 51 Building Entrance Protectors Primary Protectors protect telecom facilities and equipment from abnormally high voltages and current ◦ Located at the building entrance (indoor or outdoor) ◦ Protects against high voltages and currents Secondary Protectors ◦ Located nearer to the equipment ◦ Add a second layer of protection that is more precise and faster in its voltage protection ◦ Often includes other elements such as current protection and filters 52 Two Categories of Communication Cable Electrical Protection Shield and other metallic cable elements: 1. ◦ ◦ Bond directly to the closest available ground Use approved bonding connectors Conductive communication wires: 2. ◦ Employ building entrance protectors 53 Circuit Protectors ‘Primary protectors’ are most typically made from carbon blocks, gas tubes, or solid state ◦ Installed immediately adjacent to the exposed cable’s point of entrance ◦ Bond a grounding conductor directly to the protector’s ground 54 Carbon Protection Modules The earliest style available An air gap between carbon elements is adjusted to arc at about 300 volts and send the current to a ground conductor Can short permanently Limited lifespan Still available, but they have been replaced by gas and solid state technologies 55 Gas Protection Modules Provide a discharge gap between two electrodes sealed in a ceramic envelope containing inert gases Usually arc at a lower voltage than carbon, providing better protection Have a much longer lifespan than carbon 56 Solid State Protection Modules Longest lifespan Solid state construction provides nanosecond response time External failsafe mechanism which permanently grounds the module under sustained high current conditions More expensive but most reliable 57 Sneak Circuit Protectors Sneak currents are unwanted currents that find their way into a communication system Secondary protectors are typically made from heat coil, sneak-current fuse, or thermal resistors Current Protection Module image: www.siemon.com 58 Protectors Best Practices Accessible for maintenance Close to the power service entrance Limit the length of conductors & keep straight Ground the protector panel to nearest grounding electrode system with #6 ground wire Protect all conductors in the cable Protect both ends of the cable Leave space for additions 59 Grounding the Equipment Grounding the equipment, outside and inside. Images from the National Association for Amateur Radio image: www.arrl.org 60 3 Principles for Communications Grounding Equalization ◦ minimize differences in ground potential ◦ use short, direct path with large conductor Diversion ◦ bonding conductor is connected to the systems ground at both ends ◦ bonding conductors follow communications conductors and can easily divert transients away from the communications conductor Coupling ◦ the closer the bonding conductor is to the communications cable, the greater the mutual coupling 61 Types of Grounds A building may have six defined types of grounding and bonding systems designed to provide overall protection for the building and its occupants: ◦ ◦ ◦ ◦ ◦ ◦ Lightning protection system Grounding electrode system Electrical bonding and grounding system Electrical power protection system Telecommunications bonding and grounding system Telecommunications circuit protector system 62 Building Grounding Electrode System Established by the electricians. Consists of ◦ connection to earth ground ◦ conductor ◦ bonding points Attached to the system are: ◦ Electrical Safety grounds ◦ Any metallic elements of the electrical installation including tray, conduit, electrical boxes, panels, etc ◦ Cable shields and building entrance equipment Lightning protection should be an independent ground that never enters the building 63 Telecom Grounding Choices Direct attachment to the closest point in the building’s electrical service grounding electrode system. ◦ Preferred because telecommunications cabling and power cabling must be effectively equalized Select the nearest accessible location to: ◦ The building ground electrode system or, ◦ An accessible electrical service ground or, ◦ Gas Pipes Cold water supply pipes are a poor choice today Plastic pipes are now commonly used In many jurisdictions connections to water pipes for safety grounding is no longer permitted because of the increased use of nonmetallic pipe. 64 Attachment to the cable shield Bonding connectors include “coins”, clips, clamps, “beaver” bonds and other device ◦ ◦ ◦ ◦ ◦ Used with outside plant cables (some indoor) Used is splices, building entrances Sized based on the cable size (pair count) Consist of: a base, a top, and nuts (may also include a shoe) Have teeth to create a good electrical connection with the shield of the cable. image: www.3m.com images: prgodin 65 Additional Bonding Products Copper bond bar - different lengths available - holes and slots for attachment Bonding braid Insulator tubing Diaper wrap for encapsulating splices 66 The 607B Standard 67 The 607B Standard ANSI TIA 607B covers grounding and bonding for telecommunications Canadian Electrical Code ◦ published by CSA ◦ coordinated product test standards ◦ similar, but not identical to, the NEC 68 Grounding and Bonding Standards from the following organizations are the four main sources for information about grounding and bonding codes and practices ◦ National Electrical Code (NEC) ◦ ANSI/TIA-607B: Commercial Building Grounding and Bonding for Telecommunications ◦ Underwriters Laboratories UL-497: Protectors for Paired Conductor Communication Circuits ◦ IEEE Standard 142-1991: Grounding of Industrial and Commercial Power Systems 69 Protection System Planning Advantages to planning early: ◦ better access to installation areas ◦ system components can be protected from mechanical and environmental effects ◦ improved aesthetics ◦ it is generally more cost effective to meet protection requirements during the initial construction 70 Bidding and Contracts even if the customer has not requested protection equipment consider including it in your bid if it does not already exist who is responsible for each protection system? every item in the protection system adds value for your customer ◦ customers have a right to know what they are getting 71 The 607B Standard Discusses a grounding system for the telecommunications equipment Easy standard to understand Main elements of the standard: ◦ TBB (Telecom Bonding Backbone): A grounding conductor that runs through the TR, ER and EF ◦ TGB (Telecom Grounding Backplane): Bonding plate in each of the rooms ◦ TMGB (Telecom Main Grounding Backplane): A larger, centralized bonding plate placed near the grounding electrode system ◦ TEBC (Telecom Equipment Bonding Conductor): cable assemblies that connect between the TGBs and the equipment 72 73 Building Grounding Electrode An Electrician connects the system to the grounding electrode. The Grounding Electrode is a direct, low-resistance connection to the earth used as the electrical safety ground. The Telecom Bonding Conductor (TBC) connects between the Grounding Electrode and the TMGB 74 TMGB Telecommunications Main Grounding Busbar ◦ Central connection point typically located in the EF ◦ Standard defines its construction (dimensions, copper construction, hole sizes) ◦ May also be used for grounding building entrance protection image: www.homebrella.ca 75 TGB Telecommunications Grounding Busbar ◦ Located in everay TR and ER ◦ Standard defines its construction (dimensions, copper construction, hole sizes) 76 TBB Telecom Bonding Backbone The TBBs originates at the TMGB Consist of: ◦ Stranded 6 AWG (minimum) copper conductor, insulated with green jacket ◦ Routed with minimum bends or changes in direction. Must not be cut (use a tap connection) Tap Connection 77 http://www.electrical-contractor.net/forums http://www.panduit.com Example of compression/crimp connectors for attaching to the TBB 78 TBB Planning When planning TBB installation: ◦ Be consistent with the design of the telecommunications backbone cabling system ◦ Use multiple TBBs if the building size permits it, but they must be bonded together at the top floor ◦ Bonding conductors between a TBB and TGB must be continuous and routed as directly as possible ◦ Visibly labeled and physically secure 79 TBB/TGB Connection The TBB is connected to the equipment with a BCT (Bonding Conductor for Telecom) The connections should be compression (crimp or screw terminal) Example of acceptable connectors at the TGB and equipment images from www.panduit.com 80 81 TIA/EIA 607B - Overview 1 A permanent infrastructure for telecommunications grounding and bonding, independent of the telecommunications cabling Minimum 6 AWG (large as 3/0 AWG) insulated bonding conductors are installed through every major telecommunications pathway (TBB) TBBs are directly bonded to a telecommunications grounding busbars. 82 TIA/EIA 607B - Overview 2 TMGB are directly bonded to the electrical service ground All TBBs end on the TMGB Each TBB should be a continuous conductor from the TMGB to the farthest TGB Intermediate TGB should be spliced to the TBB with a short bonding conductor 83 TIA/EIA 607B - Overview 3 Each TGB is also directly bonded to building structural steel and other permanent metallic systems, if close and accessible Each TBB that reaches a TGB location must be bonded to the TGB 84 TIA/EIA 607B - Overview 4 TGB and TBB must be visibly labeled and physically secure All of the grounding busbars are used by telecommunications systems installers for their grounding requirements 85 TR Telecommunications Rooms ◦ In a telecommunications closet, suitable ground options include: Building structural steel. An electrical receptacle box or approved conduit connection. A combination of these that is accessible. An already established communications ground. 86 Backbone Cable Protection Cables that are inside a building are not usually considered exposed, but protective measures are occasionally advised ◦ High-rise and low-wide buildings and buildings close to substations or heavy industrial facilities Electrical power cable should be physically separated from communications cables 87 Backbone Cable Protection communications cables should be routed near the center of the building a lightning protection system is advised exposed cables entering the building should be protected and grounded bonding should be installed along each backbone cable pathway 88 Inspection Visual inspection can usually reveal problems, such as: ◦ ◦ ◦ ◦ Loose connections. Corrosion. Physical damage. System modifications. Note: During any service work, the installer should visually inspect bonding connections. 89 Review 90 Summary All telecommunications systems require grounding and bonding systems. Several associations provide codes, standards, and minimum requirements for installing these systems. ANSI/TIA-607, “Commercial Building Grounding and Bonding Requirements for Telecommunications,” is the primary source of installation information. Another important source is the NEC 91 Summary Grounding and Bonding ◦ Provide additional safety factors where equipment and people are involved. It protects people from being shocked by voltage potentials. It provides a point of discharge for static electricity. It reduces or eliminates stray voltage and current. ◦ Reduce the effects of lightning, static electricity and ground faults ◦ Properly grounding the shields of cables can help reduce noise and crosstalk from adjacent cables. 92 Summary A grounding and bonding network is made up of insulated copper conductors. These conductors are run in parallel with the telecommunications cables, and link rooms containing telecommunications equipment to a common ground. The recommended size for these conductors range from No. 6 to No. 3 /0 AWG insulated copper 93 Summary These conductors are bonded to solid copper grounding busbars, which are installed in the entrance facility, the main telecommunications room, and all other telecommunications rooms. In addition to the conductors that run throughout the building, telecommunications equipment, frames, cabinets, raceways, and protectors are grounded to the busbars 94 Summary The busbars throughout the building are bonded together with a backbone cable of at least No. 6 AWG insulated copper. This backbone cable is also connected to the main grounding busbar, which is bonded to the electrical service (power) ground and an earth ground 95 Summary Telecommunications circuit protectors are used to protect telecommunications facilities and equipment from abnormally high voltages and currents. This protection is in addition to the requirements and recommendations for grounding and bonding telecommunications systems Documentation makes your job easier and helps you and your networks work more efficiently END prgodin @ gmail.com 96