Performance in the data center is affected by equipment not being grounded or bonded; therefore, the Telecommunications Industry Association (TIA) is working to expand its one and only existing grounding and bonding performance standard, ANSI-J-STD-607-A. TIA decided in late 2007 to update this data communications grounding and bonding standard for low-voltage installations, with a “B” edition planned for September 2009. There are some new requirements that will be affecting electrical contractors.
This “B” edition of ANSI-J-STD-607 is being drafted with requirements in mind for the data center and other areas, such as the industrial environment and towers and antennas.
For safety reasons, low-voltage systems—such as electrical services and/or telecommunications equipment—are required to be bonded to ground per national and local electrical codes and industry standards. At the same time, grounding screened or shielded cabling systems affects performance.
The goal of grounding and bonding cabling is reached when the noise—induced by electromagnetic interference—is carried to ground along the screen or foil shield that protects the transmission of data over the conductors from that external noise. Any metallic component that is part of the data center infrastructure, such as equipment, racks, ladder racks, enclosures, cable trays, cable with a screen or foil shield, etc., must be bonded to the grounding system.
The data center requirements planned for TIA-607-B
Each data center (computer room or equipment room) will have a MESH-bonding network (MESH-BN). The MESH-BN is a conductor grid that covers the entire computer room or equipment room space. The ideal spacing for the grid is between 2 and 4 feet. The computer or equipment room will include a TMGB or a TGB to bond the TBB to the computer room or equipment room MESH-BN. See next page for a list of definitions.
Bonding connections for the MESH-BN will be the following:
• 1/0 AWG (8.33 mm diameter) or larger bonding conductor to the TMGB or TGB in the computer room
• 6 AWG (4.1 mm diameter) or larger bonding conductor to each computer or telecom cabinet/rack (not bonded serially)
• 6 AWG (4.1 mm diameter) or larger bonding conductor to HVAC equipment
• 4 AWG (5.9 mm diameter) or larger bonding conductor to each building steel column in the computer room
• 6 AWG (4.1 mm diameter) or larger bonding conductor to each metallic cable tray and cable runway in the room
• 6 AWG (4.1 mm diameter) or larger bonding conductor to each metallic conduit, water pipe and air duct in the room
• 6 AWG (4.1 mm diameter) or larger bonding conductor to every 4 to 6 access floor pedestal in each direction
• A bonding conductor to the ground bus for each panel board serving the room (see sizing per National Electrical Code 250.122 and manufacturers’ instructions)
All noncurrent-carrying metallic enclosures in the computer room are individually bonded to the MESH-BN, the TGB or TMGB in that computer room. No daisy-chaining is allowed. Instead, enclosures have their own dedicated bonding conductor to the MESH-BN, TGB or TMGB.
Local area network (LAN) equipment, such as switches and routers, should be grounded and bonded per the manufacturer’s installation instructions. If the rack that holds the LAN equipment is properly grounded to the TGB, the LAN equipment can be bonded to the rack. RGBs are recommended for cabinets and racks that need to support multiple equipment bonding conductors.
The bonding conductors used in the computer room to bond components to the MESH-BN or RGB must be stranded copper conductors. They should be routed so they are long enough to meet requirements to bond the component to the MESH-BN or RGB and secured at no greater than 3-foot intervals. The conductors must be routed to avoid any damage to the conductors and listed as suitable for grounding applications. They should be available for use in the space in which they will be placed and have a green jacket (with or without a yellow stripe). The conductors must be installed using low-emission exothermic welds and bonded to each end of the conduit using a grounding bushing or a minimum 6 AWG conductor, when the conductor is in ferrous metallic conduit that is more than 3 feet long.
And, on top of all that, each telecom grounding and bonding conductor has to be labeled.
TIA-942 for Data Center Cabling states that computer room grounding begins with a grid of copper that runs between the supports for the access floor. The grid also can be of No. 6 AWG insulated wire. Every sixth or third support is grounded to this strip with the No. 6 AWG wire, as are the racks and cabinets; heating, ventilating and air conditioning equipment; electrical conduit; and cable raceways.
To make things more interesting, two more standards are coming out soon: TIA-606-A, Addendum 1, which was written only for equipment rooms and data center equipment rooms that will include additional computer room labeling requirements, and TIA-606-B, the update to the more generic labeling standard that may also include computer room requirements.
Industrial requirements planned for TIA-607-B
Requirements for the industrial environment will be in a separate but mandatory annex to ANSI/TIA-J-STD-607-B. A star grounding system can be installed with the industrial control equipment. The benefit of this system is that it is separate from the building’s grounding system and does not rely on it. This grounding system controls current by using the existing building ground’s PE for high-noise circuits and provides an FE grounding circuit for sensitive equipment, including communications circuits. Lightning-induced surges and electrostatic discharge paths need to be controlled to minimize any impact and damage—a bonding ring may be used to provide bonding points within a large room or facility, and screened cables entering a building have to be bonded to the main earth terminal where they enter.
The building’s equipotential grounding and bonding system—equipotential bonding prevents potential differences and dangerous contact voltages between protective earth and metallic systems—looks similar to the star, but the equalization conductors form a mesh attempting to equalize voltage offsets at all points within the system. The conductor gauge, length and frequency of the noise will directly impact the performance of the equipotential grounding and bonding system.
The equalization bonding conductor must be installed in parallel with the communications cable to divert the ground noise from the communications circuit and shield. In some cases, the nearest building steel structures between the machine and control cabinets may be used for bonding. A minimum 1-inch copper braid (strap), or No. 8 AWG conductor, has to be used for equipment bonding.
This development work is meant to help people avoid some of the reliability and safety issues associated with improper grounding. These could include the cabling system becoming a primary source of interference and emission; an adverse effect to the performance of electronic equipment—from the circuit board to the network system—when the grounding, bonding and shielding techniques are poorly designed or improperly applied; any problems associated with power distribution systems that could be directly or indirectly related to bonding and grounding issues; personal injury from an electric shock caused by improper grounding, causing serious injury and considerable expense; and potential fire hazards that could occur when heat is generated from electrical surges occurring on a high-impedance grounding and bonding path.
Remember, whether it is a commercial building, a data center, or an industrial building, all other elements of a protection system are useless without proper grounding and bonding. When the metallic conductors in a telecommunications facility are bonded, everything is at equal potential. Bonding is done to connect all conductors to the same earth. Some examples of what needs to be connected are antenna towers, shields on incoming coaxial cables, the screens or foils on shielded twisted-pair cables, cable trays, cabinets and racks, computer room signal reference grids, and telephone room equipment. Find out when this performance standard is coming out, and add the final requirements to your skill set.
MICHELSON, president of Jackson, Calif.-based Business Communication Services and publisher of the BCS Reports, is an expert in TIA/EIA performance standards. Contact her at www.bcsreports.com or firstname.lastname@example.org.