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.
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Even though FIPS PUB 94 that introduced SRGs was withdrawn from publication in 1997, the standard is still commonly referenced today and industry standards routinely specify or recommend a ground reference grid.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.
- 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.
27 Comments
Miles Allgood says:
bookmarked!!, I love your site!|
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 [...]
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 [...]
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 [...]
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
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 [...]
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.
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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.
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.
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.”
Tomi Engdahl says:
8 key components for successful grounding and bonding
http://www.cablinginstall.com/articles/2013/12/cpi-key-ground-bond-components.html
Tomi Engdahl says:
Grounding article gets grounded
http://www.cablinginstall.com/articles/print/volume-21/issue-7/departments/grounding-article-gets-grounded.html
Tomi Engdahl says:
Grounding clamp for raised-floor pedestal
http://www.cablinginstall.com/articles/2014/04/burndy-pedestal-clamp.html
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.”
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
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.
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.
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.
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.
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
Tomi Engdahl says:
DOCSIS 3.1 noise mitigation: Check your grounds
http://www.broadbandtechreport.com/articles/2018/01/docsis-3-1-noise-mitigation-check-your-grounds.html?cmpid=enl_btr_weekly_2018-01-30&pwhid=6b9badc08db25d04d04ee00b499089ffc280910702f8ef99951bdbdad3175f54dcae8b7ad9fa2c1f5697ffa19d05535df56b8dc1e6f75b7b6f6f8c7461ce0b24
Since the dawn of time, individuals have known that they need to protect themselves from lightning. In the beginning, humans were only concerned with protecting themselves. As time went on and infrastructures were constructed, it became evident that those things needed to be protected, too. Through trial and error, society figured out how to design and construct lightning rods that could take the energy generated from lightning and harmlessly return it to the earth.
Protection from electricity that ranged from lightning, with its mega-voltages and current, to the micro-current of a small static charge was now needed.
A balancing act
With the advent of DOCSIS 3.1, companies not only have to be concerned that the grounds in hubs and headends are adequate in the sense that they meet the absolute ohm specification of the ground for safety of people and protection of property, but also that the various elements of that ground are balanced. That means that they must make sure that each of the various metallic “runs” that make up the ground have the same resistance.
There are various elements that make up the hub and headend ground, including shelves that are bonded to racks with screws and wires, racks that are bonded together to make aisles, as well as aisles that are bonded to bus bars.
It is difficult to get these elements balanced, to make sure that each has the same resistance.
Each place that these elements are bonded is an ingress point for noise. There are thousands of them. If there is a loose fit, a bad connector, scrape on a shield or anything that compromises the connection, the chance of ingress is better.
What balances or unbalances the elements?
Assume that the grounds are connected to one another. Assume again that they are effective and meet all safety specifications. However, sometimes there are aspects that can cause bonds to possess slightly different resistances from like bonds, including paint, torque, washers, length of cable, and the makeup of ground wires and cables.
Balancing the elements of a ground is always important because of the antennas that imbalances create for RF.
Because of potential energy coming into the plant, when we go from 64-QAM (quadrature amplitude modulation) to 256-QAM channels, we need to lower our noise floor by 3 dB just to stay even with MER (modulation error rate) and BER (bit error rate). Bonding up to 32 of these channels adds to the potential for interference, for noise.
What can be done to reduce noise?
We want to keep the noise floor as low as possible. However, with advanced digital technologies, we need to have less noise just to stay even. By balancing the ground circuits, noise is reduced. Lab experiments and tests in actual hubs confirmed that if an unbalance of 0.8 ohms in the ground circuits can be reduced to 0.3 ohms, the noise floor in the 5 MHz to 50 MHz spectrum can be reduced by 8 dBmV.
However, the resistance of these daisy-chained grounds varied by 1.0 ohm from rack No. 1 on the left to rack No. 5 on the right. In other words, those grounds were unbalanced.
How to determine if grounds are balanced
We cannot measure the resistance value of a ground at a shelf or similar place in a hub or headend. We can, however, easily measure and compare the continuity and balance of the various ground circuits of a hub or headend.
To measure ground balance in a hub or headend, a clamp-around ground tester that measures to a tenth of an ohm is required. All clamp-around testers use Ohm’s Law to calculate resistance.
If the path of least resistance is all metal (does not involve any soil), the resistance measurement is not the resistance of a ground, but rather of the continuity of the metal circuit. When looking for unbalanced ground circuits in hubs and headends, that is what is done.
Fixing the balance
Daisy-chained ground circuits can be changed to home runs if the headend and hub grounds are not balanced.
Other environmental factors also need to be considered. All kinds of noise generators, like air-conditioners and impulse motors, are being installed. Are they grounded and are the grounds tested? These noise sources make it more urgent that grounds be balanced to reduce potential points of ingress for noise.
Tomi Engdahl says:
DOCSIS 3.1 noise mitigation: Check your grounds
http://www.broadbandtechreport.com/articles/2018/01/docsis-3-1-noise-mitigation-check-your-grounds.html?cmpid=enl_btr_docsis_31_2018-02-22&pwhid=6b9badc08db25d04d04ee00b499089ffc280910702f8ef99951bdbdad3175f54dcae8b7ad9fa2c1f5697ffa19d05535df56b8dc1e6f75b7b6f6f8c7461ce0b24
Since the dawn of time, individuals have known that they need to protect themselves from lightning. In the beginning, humans were only concerned with protecting themselves. As time went on and infrastructures were constructed, it became evident that those things needed to be protected, too. Through trial and error, society figured out how to design and construct lightning rods that could take the energy generated from lightning and harmlessly return it to the earth.
A balancing act
With the advent of DOCSIS
3.1, companies not only have to be concerned that the grounds in hubs and headends are adequate in the sense that they meet the absolute ohm specification of the ground for safety of people and protection of property, but also that the various elements of that ground are balanced. That means that they must make sure that each of the various metallic “runs” that make up the ground have the same resistance.
Elements of the hub and headend ground
There are various elements that make up the hub and headend ground, including shelves that are bonded to racks with screws and wires, racks that are bonded together to make aisles, as well as aisles that are bonded to bus bars.
Why balance is important
Balancing the elements of a ground is always important because of the antennas that imbalances create for RF. But we had enough power difference between the signal and the noise to more-or-less harmlessly “absorb” the noise. What changed?
Because of potential energy coming into the plant, when we go from 64-QAM (quadrature amplitude modulation) to 256-QAM channels, we need to lower our noise floor by 3 dB just to stay even with MER (modulation error rate) and BER (bit error rate). Bonding up to 32 of these channels adds to the potential for interference, for noise.
By balancing the ground circuits, noise is reduced. Lab experiments and tests in actual hubs confirmed that if an unbalance of 0.8 ohms in the ground circuits can be reduced to 0.3 ohms, the noise floor in the 5 MHz to 50 MHz spectrum can be reduced by 8 dBmV.
How to determine if grounds are balanced
We cannot measure the resistance value of a ground at a shelf or similar place in a hub or headend. We can, however, easily measure and compare the continuity and balance of the various ground circuits of a hub or headend.
Fixing the balance
Daisy-chained ground circuits can be changed to home runs if the headend and hub grounds are not balanced.
Tomi Engdahl says:
Key grounding and voltage
considerations in the data center
http://viewer.media.bitpipe.com/979246117_954/1296228818_955/SchneiderElectricsDataCenterSO033163EGuide012611.pdf
Circulating ground currents create their own electrical noise, so are to be avoided. I
n
principle, they’re easy to stop. Just keep everything at the same electrical potential or
voltage. Current will only flow between two points that have a difference of potential.
(Recall how static discharge occurs.) If we ground everything together with
heavy wires, then everything should be at “equal potential” and no current will flow. Not surprisingly, this
is called an “equal potential ground” and is exactly what J
-
STD
-
607
-
A is trying to achieve.
The difficulty is doing it in a practical way. It’s unr
ealistic to weld everything in the building
or even in just the data center, together with heavy copper bars.
connecting to building ground. This is a safety
issue, absolutely required by code. A good telecommunications ground can be built as a
“separate system” all th
e way to the electrical vault, although it should really be bonded to
building steel and local electrical panels at various places along the way. It can even have
its own set of ground rods if that becomes necessary to approach the lower 5
-
Ohm ground
resis
tance recommended for telecommunications services. But these ground rods had better
be bonded to the main electrical ground for the building. If you have a vendor who tells you
they require a “separate ground” connected only to its own ground rods, tell th
em to consult
a qualified engineer or code authority. God forbid there should ever be something called a
“ground fault” in your incoming, high
-
voltage, building electrical service. The soil resistance
between the separated grounds will result in a huge vol
tage difference if a “fault” occurs,
and the resulting current will instantly boil the earth.
The force of the explosion could put
the basement slab on the second floor, and the resulting power surge on your “separate
ground” could fry everything, and ever
ybody, that’s in contact with a grounded device.
the code requirement f
or a “neutral
bond” on the secondary (“load”) side of a transformer. The code defines a transformer, such
as is often found in a large PDU and a full
-
time UPS, as a “separately derived source.” This
means that a neutral
-
to
-
ground bond is required. How this
is connected to the
telecommunications static ground is sometimes a little tricky and can require some analysis
We should not close this discussion without at least mentioning the “ultimate” in
telecommunications grounding practice
–
the “PANI”
ground. This approach actually divides
the ground bar into four sectors identified as “producers,” “surge arrestors,” “non
-
isolated”
and “isolated” ground networks (PANI). This is an even more exacting method of ensuring
that ground currents flow within th
e ground bar in a way that further avoids ground current
interaction. PANI grounds are used in major telecommunications carrier installations and are
often required by the military.
The electrical trades just don’t understand telcom grounding.
In short, good data center grounding requires understanding, careful planning (as does any
technical design), proper execution and good supervision. It is not inexpensive, but it could
easily make the difference between reliably functioning equipment and never-ending data
errors and failures.
Tomi Engdahl says:
ETSI EN 300 253
Environmental Engineering (EE);
Earthing and bonding of ICT equipment powered by -48 VDC in telecom and data centres
http://www.etsi.org/deliver/etsi_en/300200_300299/300253/02.02.01_60/en_300253v020201p.pdf
Bonding Network (BN), (Recommendation ITU-T K.27 [i.2]): set of interconnected conductive structures that provides an “electromagnetic shield” for electronic systems and personnel at frequencies from Direct Current (DC) tlow Radio Frequency (RF)
Common Bonding Network (CBN), (Recommendation ITU-T K.27 [i.2]): principal means for effective bonding and earthing inside a telecommunication building or data centre
DC return conductor: (+) conductor of the -48 V or -60 V secondary DC supply
MESHed Bonding Network (MESH-BN), (Recommendation ITU-T K.27 [i.2]): bonding network in which all associated equipment frames , racks and cabinets and usually the DC power return conductor, are bonded together aswell as at multiple points to the CBN
MESHed Isolated Bonding Network (MESH-IBN), (Recommendation ITU-T K.27 [i.2]): type of IBN in which the components of the IBN (e.g. equipment frames) are interconnected to form a mesh-like structure
To achieve safety the standards EN 60950-1 [3], EN 41003 [4] and CENELEC HD 60364-4-41 [1] shall be applied in the design of the equipment. The installation of PEs and equipotential bonding conductors shall be carried out in accordance with CENELEC HD 60364-5-54 [2].
The AC power distribution inside a telecommunication or ICT building shall conform to the requirements of the TN-S system. This requires that there shall be no PEN conductor within the building
The integration of the DC return conductor is addressed in clauses 5.4 and 6.1. When existing equipment requires replacement, it is essential that equipment design and installation conforms to a single standard without ambiguity.
Tomi Engdahl says:
Why effective shielding matters in your structured cabling system
https://www.cablinginstall.com/articles/2019/03/why-effective-sheilding-matters-to-structured-cabling-systems-belden-blog.html?cmpid=&utm_source=enl&utm_medium=email&utm_campaign=cim_data_center_newsletter&utm_content=2019-03-18&eid=289644432&bid=2395486
There’s no doubt that a cabling system’s physical characteristics impact performance and reliability – but there’s another component of a high-performance cabling infrastructure to keep in mind: proper grounding, bonding and shielding.
In a recent Belden blog about grounding and bonding in telecommunications rooms, we covered the basics of grounding and bonding. Now we’re ready to talk about the other important component of a grounding and bonding system: an effective shielding system!
Why is Effective Shielding Necessary?
Depending on the surrounding environment, a cable can pick up interference being released from nearby sources. Shielding reduces the effects of this kind of EMI (electromagnetic interference) in cabling systems, which are usually areas of very high EMI.
Effective shielding protects cables from signal interference and increases practical operating bandwidth levels. The success of your shielding system depends on several factors:
Quality of cable installation and proper cable handling
Quality and reliability of shield terminations (the foil connection needs to make good contact with the connector housing)
Balance of the twisted pairs
Impedance of the ground connection
Ground potential difference between local and remote grounds
Myths About Effective Shielding
Effective shielding also prevents ground loops, which develop when there is more than one ground connection. If there’s a difference in common-mode voltage potential at these ground connections, noise is induced onto the cabling.
Many people think they can use an unshielded patch cord at the other end of the system’s shield, believing that this will break the flow of current from a large ground coupling and prevent a ground loop. But doesn’t correct the problem. If a common-mode voltage potential difference larger than 1v at each ground is present, then current will travel that path. Removing the shield at one end simply leaves it exposed to the next danger point. The problem still exists (and will likely come back to bite you later).
Belden recommends grounding at both ends of a shield. Otherwise, there may be a common-mode voltage potential difference and current may be flowing, leading to a ground loop. There should always be less than 1 Ohm resistance path to ground.
Effective Shielding: What the Standards Say
The standards that guide grounding, bonding and shielding include IEC 60364-1 and ANSI/TIA-607-C.
TIA standards dictate the following:
The shield of shielded, twisted-pair cables shall be bonded to the SBB or PBB (generally through terminating the cable shield to the connector)
The connector is bonded to the metallic panel frame, which is bonded per TIA guidelines
Voltage higher than 1 Vrms between the shielded cabling system at the equipment outlet and the ground wire of the corresponding electrical outlet expected to power the equipment isn’t grounded and, therefore, isn’t recommended.
The Importance of Grounding and Bonding a Shielded System in the Telecommunications Room
https://www.belden.com/blog/smart-building/the-importance-of-grounding-and-bonding-a-shielded-system-in-the-telecommunications-room