Although the basic principles of grounding and bonding apply to telecom systems, you must understand the new terminology and unique grounding needs that sensitive systems require.
With the increasing demand for computer network installations, datacom grounding and bonding has become a growing opportunity for electrical contractors. While similar grounding principles apply, understanding the datacom terminology and special considerations can be challenging. To help you wade through the industry's jargon, we'll define terms and discuss the basic schematics of a properly grounded and bonded datacom network.
Are electrical grounding and datacom grounding the same? As with traditional electrical grounding, you should ground datacom networks and equipment to the electrical service. However, simply grounding to structural steel isn't enough. The sensitivity of this electronic equipment requires that you effectively equalize the datacom and power cabling to prevent loops or transients that can damage the equipment. This requires designing a grounding and bonding system that goes beyond the basic "green wire" methodology.
Unpredictable and intermittent data loss and outright computer failure can result from a transient. To help ensure the safety and operation of sensitive computer equipment, you should install an effective grounding system to prevent such disturbances.
To ensure effective equalization, you should attach the datacom ground directly to the electrical service ground. However, you can use an electrode, such as a ground rod or other grounding electrode system, when no electrical service is present.
Schematics of a typical datacom grounding system. A datacom grounding system contains the following components:
• A telecom bonding conductor;
• A telecom main grounding busbar (TMGB);
• A telecom bonding backbone (TBB);
• A telecom grounding busbar (TGB) at each closet; and
• A telecom bonding backbone interconnecting bonding conductor (TBBIBC).
The system begins at the electrical service entrance, travels to the TMGB, and continues through to each TGB located in individual datacom closets on each floor of the building structure, finally looping back around to the original TMGB.
The telecom entrance facility (TEF) includes the entrance point at the datacom service and the space where the inter- and intra-building backbone facilities join. You can locate datacom-related antenna entrances and electronic equipment in the TEF.
Telecommunications main grounding busbar (TMGB). The TMGB is the dedicated extension of the building grounding electrode system for the datacom infrastructure. Because it's the central attachment point for TBBs and equipment, it should have easy access by datacom personnel.
The TMGB is a predrilled copper bus bar with standard NEMA bolt-hole sizing and spacing for the particular lug connection used. It should be large enough to satisfy today's applications and accommodate future growth. The TMGB should have a minimum thickness of 6 mm and width of 100 mm. You'll find varieties of ground bars available, and some come as a kit you can customize to meet specific requirements of the application. Pre-welded exothermic pigtails are available in a variety of conductor sizes and lengths, insulated or bare, ready for your attachment to the building ground.
Electrotin plating results in reduced resistance. However, you must completely clean any mating surfaces if they're not plated. If you have datacom panelboards located with the TMGB, you must bond the alternating current equipment ground bus (or metallic enclosure) of each to the TMGB/TGB. Make sure you maintain appropriate clearances when locating TMGBs as close as possible to the panelboards.
Telecommunications bonding backbone (TBB). The TBB is a conductor that connects all TGBs with the TMGB. It reduces or equalizes potential differences between the various datacom systems it's bonded to. The TBB should not be the only conductor providing a ground fault current return path.
Starting at the TMGB, the TBB loops throughout the building via datacom backbone pathways. It connects TGBs in every datacom closet and equipment room within the building.
You may need multiple TBBs, depending on the size of the structure and number of TGBs. Do not use water pipes or metallic cable shields as the telecom bonding backbone.
Each TBB should be an insulated copper conductor, minimum of No. 6 AWG and possibly as large as 750kcmil In a multistory building you should bond together the TBBs with a TBB interconnection bonding conductor (TBBIC), which you should locate on the top floor and at least every third floor. Don't splice TBBs unless necessary. However, if you need to splice, exothermic welds are ideal to permanently join segments of the TBB.
Telecommunications grounding bus bar (TGB). A TGB is a predrilled copper bus bar with standard NEMA bolt-hole sizing. It centrally connects systems and equipment served by a datacom closet. The TGB should be at least 6 mm thick by 50 mm wide. Like the TMGB, the TGB should be electrotin plated or cleaned prior to connecting the conductors to the bus bar. The bonding conductor between the TBB and the TGB should be continuous and run in the most direct path possible.
When the building's structural steel is grounded, you should bond each TGB to the steel within the same room with a No. 6 AWG conductor. Always use the shortest distance possible in the grounding system.
The complete grounding and bonding system. Ultimately, effective datacom system grounding and bonding means creating a continuous system in which each TGB interconnects in a loop that begins and ends with the TMGB. Using quality products will ensure the long-term success of the system. By planning ahead, today's datacom networks can work effectively and safely well into the future.
Sidebar: For More Information ...
The information in this article offers a brief explanation of how to install a datacom grounding system. To help better understand telecom grounding, consult ANSI/EIA/TIA 607, which covers requirements for datacom applications in commercial buildings. Other important standards include EIA/TIA 568-A and 569-A, which, as a set, are Telecom Building Wiring Standards. In addition, Chapter 8 of the NEC (Communication Systems) covers general requirements for grounding, bonding, and protection of low-voltage communications equipment. Also, Chapter 2 and Art. 250 discuss grounding requirements.
You should consult the Canadian Electrical Code (CEC) and other national and local safety codes where applicable.
For answers to questions about how to properly ground and bond datacom systems, a good source is the Building Industry Consulting Services International (BICSI). Contact the organization by calling (800) 242-7405 or writing to 8610 Hidden River Parkway, Tampa, FL 33637-1000.
Help also is available through the ERICO grounding and bonding information line: (800) 677-9089.