Signal reference grids in the data center

A recent white paper from APC-Schneider Electric authored by Neil Rasmussen takes a hard look at grounding practices and the use of the signal reference grid in data centers. The Grounding and the Use of the Signal Reference Grid in Data Centers paper contends that signal reference grids are automatically specified and installed in data centers despite the fact that they are usually no longer needed by modern IT equipment. Grounding and the Use of the Signal Reference Grid in Data Centers paper explains pretty the origins of the signal reference grid, the operating principles and limitations, and why they no longer are needed.

Signal Reference Grids (SRG’s) provide a low impedance equipotential plane to protect sensitive electronic equipment from transients. SRG’s can be used for proper grounding and bonding of sensitive electronic systems, such as telecommunications, RF and computer installations.

The signal reference grid is constructed using (in order of preference) flat braided copper cable, flat copper strips, or round multi-strand copper conductor. Due to the “skin effect” characteristic of high-frequency signals, flat braided copper cable offers superior performance.

From the white paper’s introduction: “The signal reference grid (SRG) is a network of copper wires typically installed below a raised floor in a data center.” “The installation of signal reference grids has been common practice for over 30 years. Further, most data center designs calling for SRGs and their use and expense are not questioned.”

Signal reference grids: myths, facts, and sensible choices article tells that choice of SRG depends on knowing what’s legitimately true and patently false about grounding, bonding, and electrical noise mitigation. Proper bonding and grounding is based on science. While there is an abundance of in-vogue Computer grounding information, some of the “facts” are unsubstantiated and can cause unnecessary confusion and expense.

Grounding and the Use of the Signal Reference Grid in Data Centers paper pretty heavily questions the need for SRG in modern data center. It is worth to read the paper. Here are some main points picked from that paper:

Even though FIPS PUB 94 that introduced SRGs was withdrawn from publication in 1997, the standard is still commonly referenced today and industry standards routinely specify or recommend a ground reference grid.

Recently, more and more data centers are being constructed on existing hard-floor environments where SRGs cannot be installed under the floor. Modern data centers can work reliably without an SRG. The reason is changes in the design of IT equipment have totally changed the susceptibility of equipment to electrical noise. The signal reference grid used in most modern data centers is no longer as important as it once was, due to changes in IT technology. Modern IT equipment uses methods for data communication which have substantially changed over time and now have dramatically reduced inter-system ground noise susceptibility.

The different types of data communication interfaces are classified into susceptibility classes:

Susceptibility class: Low immunity
Interfaces in class: Parallel ports, RS-232 ports, Proprietary backplane, Video cables
Characteristics: Copper cabling with ground referenced signals. Any shift in ground voltage between the interconnected equipment is superimposed on the data signal. Inter-system ground noise of 0.1 volt or even less can interfere with communication (depends on interface).

Susceptibility class: Partial immunity
Interfaces in class: Modbus, RS-485, SCSI
Characteristics: Use balanced or differential signal transmission that is not ground referenced. Inter-system ground noise of 10 volts or more can interfere with communication when it exceeds interface “common mode range”.

Susceptibility class: High immunity
Interfaces in class: Ethernet
Characteristics: Copper communication interfaces that have a balanced or differential signal transmission with full transformer isolation at both ends (Ethernet over 1000 volt isolation). Communication protocols have built-in error correction.

Susceptibility class: Total immunity
Interfaces in class: Fiber optic, Wireless
Characteristics: Inter-system ground noise does not have any effect on communications.

My own addition to list would be that analogue audio signals if your system uses then go to low immunity class (some properly implemented balanced line level audio signals would go to partial immunity class).

At the time the SRG was first created, the primary data interface systems were those in the “low immunity” group. Equipment communication interference reduction function of the SRG is based on the ability of the SRG to reduce inter-system ground noise. In today’s data centers data interfaces are mainly of the “high immunity” or “total immunity” classes. Only few “low immunity” interface types remain (mainly restricted to use with a single rack). There is no more need for a supplemental SRG to guarantee that communication between racks work reliably and or for electrical safety reasons.

A detailed analysis of the science and practice regarding grounding suggests the following best practices :

  • Use Ethernet or fiber for data communication in a data center where possible.
  • Interconnect racks in a row with ground bonding wires.
  • Restrict all other forms of data communication (video, SCSI, RS-232, etc.) to interconnections within a single rack or a row of interconnected racks.
  • Bond cable trays (power and data) to equipment racks.
  • Protect the data cable entry points of the data center: Any copper wires (anything that is not fiber) should go through a central location and should be properly treated (surge suppress, isolate, signal through main router etc..)

Grounding and the Use of the Signal Reference Grid in Data Centers paper says that if the above guidance is followed, then the benefits of adding an SRG are greatly diminished making SRG installations typically unjustified.

22 Comments

  1. Miles Allgood says:

    bookmarked!!, I love your site!|

    Reply
  2. Grounding issues and minimizing EMI « Tomi Engdahl’s ePanorama blog says:

    [...] go same route as the current carrying wires (live and neutral) for best performance (but also Signal reference grid approach is possible for [...]

    Reply
  3. Audio and video signal susceptibility classes « Tomi Engdahl’s ePanorama blog says:

    [...] and video signal susceptibility classes My article Signal reference grids in the data center shows that different types of data communication interfaces are classified into susceptibility [...]

    Reply
  4. HDMI and ground loops « Tomi Engdahl’s ePanorama blog says:

    [...] can handle (common mode range, CMRR). Too high voltage on the ground will still disturb the signal. Susceptibility class for this signal could be somewhere between low and partial [...]

    Reply
  5. Tomi Engdahl says:

    6 common mistakes to avoid in telecom technology grounding
    http://www.cablinginstall.com/articles/print/volume-21/issue-02/features/6-common-mistakes-to-avoid-in-telecom-technology-grounding.html?cmpid=EnlContractorFebruary282013

    To minimize costly downtime, keep clear of these common errors that can undermine investment in surge-protection technology.

    Grounding mistake 1: Not understanding impedance guidelines
    Grounding mistake 2: Wrapping ground wire
    Grounding mistake 3: Size of wire
    Grounding mistake 4: Wire connections
    Grounding mistake 5: Technology selection
    Grounding mistake 6: Lack of single grounding point

    Reply
  6. Ethernet in sensing « Tomi Engdahl’s ePanorama blog says:

    [...] over UTP is very immune to small (or even some larger) ground potential differences because Ethernet connection has full transformer isolation at both ends (1500 volt isolation). Ethernet over UTP does not cause ground loop problems. But if you use [...]

    Reply
  7. Tomi Engdahl says:

    Why grounding is critical to data center uptime
    http://www.cablinginstall.com/articles/print/volume-14/issue-5/features/design/why-grounding-is-critical-to-data-center-uptime.html

    You can gain a competitive edge with your customers by understanding and then offering network grounding/bonding expertise.

    If you’re a contractor, understanding network grounding can give you a competitive edge by advising your customers on how to improve network availability.

    Proper grounding of data center equipment, often called network grounding or the data center grounding infrastructure, is defined by TIA/EIA-942 Telecommunications Infrastructure Standard for Data Centers, and goes beyond the requirements of the National Electrical Code (NEC) to protect equipment and improve system reliability.

    Network grounding design

    The two goals of the grounding system are to equalize electrical potentials and to create a low resistance path to ground. Five basic principles are used when designing a grounding system to accomplish these goals:

    1. The grounding system shall be intentional. Careful planning must be given to network grounding, just like any other system deployed in the data center. As the grounding system is no more reliable than its weakest link, only high-quality components can be used and trained professionals must make all connections.

    2. The grounding system shall be visually verifiable. When implemented properly, you should be able to visually inspect every component of the grounding system, from the equipment, to the rack, to the common bonding network (CBN), to the earth. Such a system can be inspected for degradation and is accessible during moves, adds, and changes (MACs), ensuring long-term system reliability and scalability.

    3. The grounding system shall be adequately sized. TIA-942 provides guidelines for each component of the grounding system. Improper use of the guidelines can reduce network availability and cause premature equipment failure that contributes to increased operating costs.

    4. The grounding system shall direct damaging currents away from equipment. A grounding system that complies with TIA-942 requires each rack to bond directly to the CBN, thereby directing current away from sensitive electronics. For instance, a common error is to daisy-chain racks together. During a surge event, the entire row of daisy-chained racks becomes energized with stray current, potentially resulting in additional damaged equipment.

    5. All metallic components in the data center shall be bonded to the grounding system. The goal is to have all conductive materials at the same electrical potential to minimize current flow. Current flows when there is a difference in potential between components. If the current flows across a piece of equipment, damage may occur. Equipment, racks, cabinets, ladder racks, enclosures, and cable trays must be bonded to the grounding system.

    To avoid the problems that are common in network grounding systems, you should implement only engineered solutions that comply with accepted industry standards, such as TIA-942 and NEBS Level 3.

    Reply
  8. Carie Baudry says:

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  9. Quinn Haarstad says:

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  10. Tomi Engdahl says:

    Meltdowns Hobble NSA Data Center
    Investigators Stumped by What’s Causing Power Surges That Destroy Equipment
    http://online.wsj.com/article_email/SB10001424052702304441404579119490744478398-lMyQjAxMTAzMDAwNzEwNDcyWj.html

    Chronic electrical surges at the massive new data-storage facility central to the National Security Agency’s spying operation have destroyed hundreds of thousands of dollars worth of machinery and delayed the center’s opening for a year, according to project documents and current and former officials.

    There have been 10 meltdowns in the past 13 months that have prevented the NSA from using computers at its new Utah data-storage center, slated to be the spy agency’s largest, according to project documents reviewed by The Wall Street Journal.

    One project official described the electrical troubles—so-called arc fault failures—as “a flash of lightning inside a 2-foot box.” These failures create fiery explosions, melt metal and cause circuits to fail, the official said.

    The causes remain under investigation, and there is disagreement whether proposed fixes will work

    The Utah facility, one of the Pentagon’s biggest U.S. construction projects, has become a symbol of the spy agency’s surveillance prowess, which gained broad attention in the wake of leaks from NSA contractor Edward Snowden. It spans more than one-million square feet, with construction costs pegged at $1.4 billion—not counting the Cray supercomputers that will reside there.

    But without a reliable electrical system to run computers and keep them cool, the NSA’s global surveillance data systems can’t function.

    The joint venture said in a statement it expected to submit a report on the problems within 10 days: “Problems were discovered with certain parts of the unique and highly complex electrical system. The causes of those problems have been determined and a permanent fix is being implemented.”

    The first arc fault failure at the Utah plant was on Aug. 9, 2012, according to project documents. Since then, the center has had nine more failures, most recently on Sept. 25. Each incident caused as much as $100,000 in damage, according to a project official.

    It took six months for investigators to determine the causes of two of the failures. In the months that followed, the contractors employed more than 30 independent experts that conducted 160 tests over 50,000 man-hours, according to project documents.

    Reply
  11. Tomi Engdahl says:

    Why grounding is critical to data center uptime
    http://www.cablinginstall.com/articles/print/volume-14/issue-5/features/design/why-grounding-is-critical-to-data-center-uptime.html

    You can gain a competitive edge with your customers by understanding and then offering network grounding/bonding expertise.

    Reply
  12. Tomi Engdahl says:

    New Elastimold device enables direct 600A, 25kA-rated ground connections
    http://www.cablinginstall.com/articles/2014/01/tnb-elastimold-600a-gad.html

    New from Thomas and Betts, the Elastimold Grounding Device (GAD) provides a direct 600A, 25kA-rated connection with a removable protective cap that allows for increased safety in grounding operations for data center power cabling.

    “Very rarely do users have a direct 600-amp ground connection to connect to,” comments Chad Smith, vice president, product management and marketing, at Thomas & Betts. “Usually, they must first reduce the connection to 200 amps, and then ground the system, reducing the capability to withstand short circuits from 25kA to 10kA. The Elastimold GAD provides a direct 600A, 25kA-rated ground connection that is permanent, reliable and safe.”

    Reply
  13. Tomi Engdahl says:

    TIA revising 607 grounding and bonding standard to ‘C’ version
    http://www.cablinginstall.com/articles/2014/05/tia-607-c.html

    The Telecommunications Industry Association’s (TIA) TR-42.16 Engineering Committee on Premises Telecommunications Bonding and Grounding recently issued a call for interest for the third revision of the grounding and bonding standard—document TIA-607-C—which is initially titled “Generic Telecommunications Grounding (Earthing) and Bonding for Customer Premises.”

    According to the TIA, the TIA-607-C update will address the fact that “today’s large telecommunications facilities are built on one level.” The bonding backbone system specified in the current, 607-B, standard exhibits a vertical layout, the association explained. “This will be updated in the TIA-607-C release, which will introduce a horizontal bonding backbone topology to address this type of building. The new revision will also specify requirements for a generic telecommunications bonding and grounding infrastructure and its interconnection to electrical systems and telecommunications systems.”

    The revision also will harmonize the international and domestic standards

    “Where there is confusion with bonding and grounding, electronic systems can fail. The improper grounding of separately derived systems can lead to equipment malfunction and other data issues.”

    Reply
  14. Tomi Engdahl says:

    Bonding and grounding

    Among the standard revisions under development is the “C” version of ANSI/TIA-607, Generic Telecommunications Grounding (Earthing) and Bonding for Customer Premises. The standard is maintained by TR-42.16. TIA announced in late May that the revision process was underway. At that time it explained that the “C” update will address the fact that “today’s large telecommunications facilities are built on one level.” The bonding backbone system specified in the current TIA-607-B standard exhibits a vertical layout, the association further explained. “This will be updated in the TIA-607-C release, which will introduce a horizontal bonding backbone topology to address this type of building. The new revision will also specify requirements for a generic telecommunications bonding and grounding infrastructure and its interconnection to electrical systems and telecommunications systems.”

    The revision’s harmonization of international and domestic standards will reduce confusion within the market, the TIA noted. When announcing a call-for-interest in the revision, the TIA commented, “Domestic and international codes and standards groups have been working on correcting terminology regarding bonding and grounding for approximately 10 years. Where there is confusion with bonding and grounding, electronic systems can fail. The improper grounding of separately derived systems can lead to equipment malfunction and other data issues. Once this new revision is completed, it may also be used as a guide for the renovation of existing systems.”

    Source: http://www.cablinginstall.com/articles/print/volume-22/issue-9/features/standards/a-potpourri-of-standards-under-development-in-tia.html

    Reply
  15. Tomi Engdahl says:

    TIA-607-C bonding and grounding standard set for imminent publication
    http://www.cablinginstall.com/articles/print/volume-23/issue-11/features/standards/tia-607-c-bonding-and-grounding-standard-set-for-imminent-publication.html?cmpid=EnlCIMCablingNewsNovember302015&eid=289644432&bid=1243084

    In spring 2014 the Telecommunications Industry Association (TIA; http://www.tiaonline.org) issued a call for interest for the third revision of the TIA-607 standard document covering grounding (earthing) and bonding of telecommunications facilities.

    When issuing the call for interest, the TIA explained that one objective of the “C” revision would be to address the fact that “today’s large telecommunications facilities are built on one level.” The bonding backbone system specified in the then-current, TIA-607-B standard, exhibits a vertical layout. “This will be updated in the TIA-607-C release, which will introduce a horizontal bonding backbone topology to address this type of building. The new revision will also specify requirements for a generic telecommunications bonding and grounding infrastructure and its interconnection to electrical systems and telecommunications systems.”

    Another objective was to harmonize international and U.S. domestic grounding and bonding specifications, thereby reducing confusion within the market.

    The nearly complete draft of the TIA-607-C standard includes nine sections: Scope; Normative References; Definitions, Acronyms and Abbreviations, Units of Measure; Regulatory; Overview of Telecommunications Bonding and Grounding Systems; Telecommunications Bonding Components; Design Requirements; External Grounding; Performance and Test Requirements.

    The lengthiest of the six annexes discusses grounding and bonding of towers and antennas.

    Reply
  16. Tomi Engdahl says:

    TIA-607-C bonding and grounding standard set for imminent publication
    http://www.cablinginstall.com/articles/print/volume-23/issue-11/features/standards/tia-607-c-bonding-and-grounding-standard-set-for-imminent-publication.html?cmpid=EnlCIMCablingNewsDecember212015&eid=289644432&bid=1260178

    The latest update to the standard addresses large single-story buildings, harmonizes terminology, and includes an informative annex covering towers and antennas.

    In spring 2014 the Telecommunications Industry Association (TIA; http://www.tiaonline.org) issued a call for interest for the third revision of the TIA-607 standard document covering grounding (earthing) and bonding of telecommunications facilities. Generally the TIA issues such a call soon after it has committed to develop or revise a standard. The 607 standard series is administered by Subcommittee TR-42.16 Premises Telecommunications Bonding and Grounding.

    When issuing the call for interest, the TIA explained that one objective of the “C” revision would be to address the fact that “today’s large telecommunications facilities are built on one level.” The bonding backbone system specified in the then-current, TIA-607-B standard, exhibits a vertical layout. “This will be updated in the TIA-607-C release, which will introduce a horizontal bonding backbone topology to address this type of building. The new revision will also specify requirements for a generic telecommunications bonding and grounding infrastructure and its interconnection to electrical systems and telecommunications systems.”

    Another objective was to harmonize international and U.S. domestic grounding and bonding specifications, thereby reducing confusion within the market.

    Reply
  17. Tomi Engdahl says:

    Best practices for bonding and grounding armored fiber cable
    http://www.cablinginstall.com/articles/print/volume-19/issue-5/features/best-practices-for-bonding-and-grounding-armored-fiber-cable.html

    Armored fiber-optic cables are often installed in a network for added mechanical protection. Two types of armoring exist: interlocking and corrugated. Interlocking armor is an aluminum armor that is helically wrapped around the cable and found in indoor and indoor/outdoor cables. It offers ruggedness and superior crush resistance. Corrugated armor is a coated steel tape folded around the cable longitudinally. It is found in outdoor cables and offers extra mechanical and rodent protection.

    Installing armored fiber-optic cable has several benefits, but one inconvenience is the need to bond and ground the cable. This inconvenience can be eliminated by using a dielectric-armored cable

    During some fiber-optic installations there is a need to provide extra protection for the cable due to the installation environment. That environment may be underground or in buildings with congested pathways. Installing an armored fiber-optic cable in these scenarios would provide extra protection for the optical fiber and added reliability for the network, lessening the risk of downtime and cable damage due to rodents, construction work, weight of other cables and other factors.

    An alternative to installing armored optical cable is to place conduit and pull in the fiber-optic cable. However, placing a single-armored fiber cable is usually the more cost-effective choice.

    Proper grounding and bonding is required for the safe and effective dissipation of unwanted electrical current, and it promotes personal and site safety. Typically, fiber-optic systems do not carry electrical power, but the metallic components of a conductive cable are capable of transmitting current. This would occur if a metallic piece of the cable—such as the interlocking or corrugated armor—were to come into contact or close proximity with electrical current from sources such as exposed wiring, faulty electrical systems, lightning or other events. This creates the potential for the occurrence of several hazards, such as electrical shock, fire, damage to electronics and system failures resulting in downtime.

    Bonding and grounding of armored fiber-optic cable are simple steps in the installation process that are often misunderstood or overlooked. The National Electrical Code (NEC) and several industry standards have been established to promote safe and effective bonding and grounding practices of armored optical cables

    Pert Article 770 of the NEC, a fiber-optic cable containing non-current-carrying metallic components, such as armor or metallic strength members, is considered conductive. This is why conductive fiber-optic cables should be bonded and grounded as specified in NEC Article 770.100.

    When all the components of a system are properly bonded together and grounded to the earth, the risk associated with electrical current harming personnel or damaging property and equipment is reduced.

    The first step is to connect/bond the cable armor to a bonding or grounding electrode conductor. This can be accomplished right after the cable is accessed, and the armor is exposed. A bonding conductor or jumper is a short length of conductor, such as copper wire, that maintains electrical conductivity between two metal objects. The bonding conductor is required to be UL-listed and made of either copper or another corrosion-resistant conductive metal

    For the conductive fiber-optic cable to be fully grounded, the bonding conductor from the cable needs to be bonded to the intersystem bonding termination (if present), or another accessible location per NEC Article 770.100. The intersystem bonding termination is the device that connects the bonding conductors to the building’s grounding electrode and ultimately, to earth. Typically this is accomplished by connecting the bonding conductor to a dedicated path back to the telecommunications main grounding busbar (TMGB) or the telecommunications grounding busbar (TGB).

    The dielectric alternative

    If the fiber-optic cable in a system needs extra protection, there is an alternative to using conduit or a bonded and grounded conductive cable, such as an all-dielectric armored cable.

    Because all-dielectric armored cable has no metallic components, there is no need to ground or bond the cable.

    Reply
  18. Tomi Engdahl says:

    ANSI/TIA-607-C: A newly released version of a standard that has come a long way
    http://www.cablinginstall.com/articles/print/volume-24/issue-6/features/installation/ansi-tia-607-c-a-newly-released-version-of-a-standard-that-has-come-a-long-way.html?cmpid=Enl_CIM_ContractorReport_July212016&eid=289644432&bid=1473264

    Beginning in August, 1994 with its first publication, TIA’s 607 bonding and grounding standard has come a long way. Originally titled “Commercial Building Grounding and Bonding Requirements for Telecommunications”, the standard was developed as a response to the need for a bonding and grounding system in the telecommunications industry. There were existing standards, like those from the NEC (National Electrical Code), that specify requirements regarding the safety aspects of bonding and grounding of equipment systems. These were not sufficient because telecommunications systems needed a bonding and grounding system for performance, not safety, since telecommunications systems operate at much higher frequencies and low voltages.

    As with all revisions to standards, the references to other standards were updated and the addendums from the previous revision B were incorporated. The following is a list of key changes included in revision C.

    The contents of Addendum 1 (external grounding) and Addendum 2 (structural metal) were incorporated.
    Terms were changed to harmonize with ISO/IEC 30129
    A new section for rack bonding busbars was added with design and installation requirements.
    An illustrative example was added for a single story large building
    Recommendations for bonding connections for separately derived systems was added
    Other design and installation recommendations

    Some of the key component names have been changed to harmonize with ISO/IEC 30129.

    In addition to changing the name, the C revision has added new sections to clause 6 (“Telecommunications Bonding Components”) and 7 (“Design“) for rack bonding busbars (RBB). Within the busbar component section of clause 6, RBB are now required to have a minimum cross-sectional area equal to a 6 AWG wire and be listed.

    There is no specific length defined for the RBB

    RBBs may be installed with a horizontal or vertical orientation as shown in the figure, using insulators that provide 0.75 inches (19 millimeters) of separation.

    A multi-story building has always been used to illustrate the telecommunications bonding and grounding system. Suggestions were made to the TIA TR-42.16 committee

    A new clause 8, External Grounding, was incorporated from addendum 1 to the previous revision. It provides additional recommendations for grounding resistance (minimum requirements are met by the use of an NFPA 70-compliant grounding electrode) and grounding electrode system design. One of the suggestions for situations in which equipment may be distributed throughout a building and may be interconnected by metallic links is to add a building perimeter ground loop to supplement the bonding and grounding system for better potential equalization.

    Potential Equalization clause, TIA-607-C provides the design recommendations for the building perimeter ground loop. If separately derived electrical systems are present, they should be bonded to the same ground ring electrode.

    Bend radius was added as an installation guideline for bonding conductors. The standard requires that the conductors at the PBB and SBB maintain a minimum bend radius of 8 inches (200 millimeters). At other locations, it is recommended that the inside bend radius should be as large as practical with a minimum of 10 times the bonding conductor diameter.

    Reply
  19. Tomi Engdahl says:

    Taking the mystery out of grounding and bonding
    http://www.cablinginstall.com/articles/print/volume-9/issue-8/contents/contracting/taking-the-mystery-out-of-grounding-and-bonding.html

    A technical support team explains the TIA/EIA-607 standard and offers solutions.

    Following the AT&T divestiture of 1984, the end user became responsible for all premises cabling of voice and data. Advancements in voice communications and the convergence of voice and data have led to increasingly complex interactive systems owned and maintained by the end user. These systems require a reliable electrical ground-reference potential.

    Grounding by attachment to the nearest piece of iron pipe is no longer satisfactory to provide ground reference for sophisticated active electronics systems. Bonding is the provision of good grounding connections between elements of the grounding network. Secondary power protection is also recommended for delicate electronics.

    Every telecommunications network requires a dedicated grounding and bonding system as described in the Commercial Building Grounding and Bonding Requirements for Telecommunications (ANSI/ TIA/EIA-607) standard, which provides minimum recommendations for such a network.

    A network of this type may also be used for grounding of access and service provider equipment, data centers, broadband video distribution, security, fire, and other systems. Unfortunately, due to a general lack of familiarity with the standard, this vital grounding network is often overlooked in preparing the network design and subsequent bid requests.

    Design considerations

    A grounding and bonding network can be described as a “tree-shaped” or “star-wired” configuration of insulated copper conductors that parallel the telecommunication cable distribution and link rooms containing telecommunication equipment to a common ground. The recommended copper conductors to be used are robust in size. Branches are 6 AWG (American wire gauge, 0.1620-inch diameter). Backbone runs are commonly 2/0 AWG (0.3648 inches) or 3/0 AWG (0.4096 inches).

    Solid copper grounding busbars are installed with insulated standoffs in the equipment room (minimum 1/4×4 inches by variable length), as well as in each telecommunications room or entrance facility (minimum 2 inches high is sufficient here). Each copper busbar is purchased pre-drilled with rows of holes for attachment of bolted compression fittings.

    Active telecommunication equipment, frames, cabinets, raceways, and voltage protectors are typically grounded to these busbars with insulated stranded copper cable (minimum 6 AWG) with crimped-on lugs at each end. Two-hole lugs are often preferred for bonding at the busbar. Single-hole lugs are used at the equipment cabinet.

    The busbars are connected together with a backbone of insulated stranded (or solid) copper cable (a minimum of 6 AWG is required, and size 3/0 AWG or larger should be considered). This backbone is connected to a main grounding busbar in the telecommunications equipment room, which is bonded to the electrical service entrance ground and an earth groun

    Reply

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