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

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.

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.

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.

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.

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

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.

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.

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.

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.