A new lease on life for shielded copper cable

Category 6 foiled-twisted-pair cable’s small outside diameter and immunity to alien crosstalk favor 10-Gbit Ethernet use.

Nov 1st, 2005
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Category 6 foiled-twisted-pair cable’s small outside diameter and immunity to alien crosstalk favor 10-Gbit Ethernet use.

Shielded copper cable has taken a back seat to unshielded twisted-pair (UTP) cable in the U.S. But now, with 10-Gig-over-copper cable on the horizon and Category 6 cable on the rise, will shielded cable gain a new lease on life here?


These patch cords are part of The Siemon Company’s TERA solution, which is a PiMF/SSTP system.
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Some say it will, even if it’s only a niche in the world of installations. The small outside diameter (OD) of Category 6 foiled-twisted-pair (FTP) cable, compared to Augmented Category 6 cable, can change the fill ratio in conduits and cable pathways. These cables can also effectively ward off alien crosstalk (ANEXT) while being immune to other detrimental performance influences, like radio-frequency interference (RFI) and other noise sources, which up until now had no effect on network performance.

UTP cable, the medium of choice for many end users, remains the dominant cable in the U.S. But some in the industry believe there will be a migration toward shielded cable-specifically, Category 6 FTP-since it offers high bandwidth, can eliminate problems from ANEXT, and allows for more space in cable pathways than Augmented Category 6 cable. But shielded cable still faces an uphill climb as enterprise end users consider its high costs and contractors debate its termination challenges.

Changing attitudes

“There have been few environments where shielded is required, but it is changing,” says Bob Zahr, manager of systems engineering for Tyco Electronics’ (www.tycoelectronics.com) AMP Netconnect Division. Tyco Electronics makes the AMP Netconnect XG Copper Cabling System for 10-Gbit Ethernet applications- a system that includes shielded cable.

“People are realizing that in the next generation of 10-Gigabit Ethernet, shielding eliminates issues like alien crosstalk as well as background noise from sources that operate in the same frequency range as 10-Gigabit Ethernet- which never were an issue with lower frequency applications like Gigabit Ethernet,” says Zahr.

Shielded cable is designed to prevent noise from interfering with the transmitted signal. In pairs in metal foil (PiMF) cable, each wire pair is individually shielded, and an overall shield surrounds all four pairs. Shielded twisted-pair (STP) cable most often features a shield around each twisted-pair of wires.

FTP cable, which is sold primarily in the U.S., is a four-pair cable with an overall shield. Unlike UTP systems, Category 6 FTP systems are not susceptible to electromagnetic interference (EMI) and RFI. They prevent noise from getting onto the signal wires by reflecting or absorbing it. “I think shielded is going to be coming back,” says Ron Shaver, master instructor for BICSI (www.bicsi.org).

Some companies are aggressively marketing their Category 6 FTP solutions. During the past year, for example, Tyco Electronics conducted technology seminars in which it presented reasons why Category 6 FTP cable would be a good fit in certain installations-especially for deploying 10-Gbit Ethernet.


The shielded version of Mohawk’s Category 6 cable (above) would have a smaller OD than the GigaLAN 10 product (below). The shielded Category 6 version’s OD is 0.251 inches, while the UTP Augmented Category 6 version has an OD of 0.315 inches.
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Perhaps as evidence of the growing interest in Category 6 FTP, some manufacturers who have not been making shielded products are considering developing their own solutions. HellermannTyton (www.hellermann.tyton.com), for example, recently introduced a fully-shielded solution into the European market, and plans to introduce a shielded Category 6 solution in the U.S. in the near future. Leviton Voice and Data Division (www.levitonvoicedata.com) is also in the early stages of creating its own shielded solution. The company is evaluating several product options that it may bring to the market in the near future.

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Mohawk (www.mohawk-cable.com) unveiled products in this area in January. Mohawk makes Advance Net ScTP, a shielded version of its Category 6 design. The company offers Category 5e FTP and Category 6 FTP cables for Gigabit and 10-Gbit Ethernet applications. All of the Mohawk cables are designed for a high-noise environment. The company also plans to offer a screened option for its 6e Plus cable, an Augmented Category 6 cable (ScTP) called GigaLAN. ScTP technology includes a cable with the same core as UTP, a foil shield that covers all four-wire pairs, a drain wire, and a jacket. By comparison, FTP is often defined as four pairs of twisted cable with an overall aluminum foil shield and bound in a plastic jacket.

“I’m looking to offer a system to customers where if they want something other than traditional UTP design, we will have an ScTP design available,” says Gregory Niemiera, Mohawk technical sales and marketing manager.

10-Gbit Ethernet fuels momentum

To a large extent, the demand for screened products is being fueled by the push for 10-Gbit Ethernet applications. A 10GBase-T standard (IEEE 802.3an) will become a reality, and manufacturers now offer enterprise end users 10-Gig-over-UTP cable solutions.

At present, these solutions (which use Augmented Category 6 cables) are still being used in only a small percentage of the installations in the U.S. Since the standard is not complete, enterprise end users tend to be hesitant to have it installed. But some manufacturers believe this trend will soon change.

Niemiera estimates that 5 to 7% of the market is now seeking 10-Gbit Ethernet. In three years, however, he believes this could stretch closer to 30%. Since 10-Gbit Ethernet operates over a higher frequency than Gigabit Ethernet, it provides more potential for ANEXT; therefore, Category 6 FTP cable is seen as an appealing option.

Category 6 FTP cables are also desirable because they are about 20% smaller in their OD than Augmented Category 6 UTP, which allows for a high-density bundle without ANEXT.

Just how much of the market Category 6 FTP cable will represent is up for debate. Zahr says Tyco Electronics now sells less than 10% Category 6 FTP cable, and does not expect a significant change. “Shielded cable won’t ever be a huge percentage of the market-not bigger than 5%,” agrees Todd Harpel, director of marketing for Berk-Tek, A Nexans Company (www.berktek.com). The company makes Guardmark-6, a Category 6 FTP cable that is part of the NetClear GTS solution.

But one thing seems certain: 10-Gbit Ethernet is raising a new interest in Category 6 FTP cable.

Once popular almost exclusively in industrial settings, shielded cable is being sought out and used in a variety of installations. Signals sent through shielded technology cannot be easily tapped by an outside source. This security benefit is making shielded cable popular with the gaming industry and government. Some believe that universities and hospitals, which could be seeking a Category 6 solution for 10-Gbit Ethernet, will also soon be interested in the shielded version. Category 6 FTP could also be used by enterprise end users in high-density data centers thatare migrating from Gigabit Ethernet to 10-Gbit Ethernet.

“It’s not just for industrial,” says Valerie Rybinski, global sales engineer for The Siemon Company (www.siemon.com), which makes the TERA system. “The advantage is you have zero alien crosstalk between cables. This is appropriate for every vertical market. It will support 10 Gigabit and be robust enough to support the greater signal-to-noise margins.”

On the other hand…

But not all manufacturers are completely sold on Category 6 FTP being the primary option for 10-Gbit Ethernet in the U.S. market. Phil Chandler, lead business development manager Copper Group for Panduit Corp. (www.panduit.com), which makes TX6000 Category 6 FTP cable, points out that the media has its advantages and disadvantages.

While the key advantage is the suppression of ANEXT, Chandler says Category 6 FTP cables may only be designed to 250 MHz (per TIA/EIA 568B.2-1) while Augmented Category 6 must be designed to at least 500 MHz. Shielded cables also require extra installation time, and they are more difficult to install due to grounding and bonding practices.

“You need to thoroughly review your options and consider all the issues involved when making a decision on a 10-Gigabit structured cabling system,” says Chandler.

He also points out that while a shielded cable is superior for ANEXT performance, its internal performance may be further degraded at high frequencies due to the shielding. To truly get Augmented Category 6 performance, he says, you need to use cable designed to perform to at least 500 MHz.

Chandler notes that Category 7 SSTP, or PiMF, cable, which is about the same size as Augmented Category 6 UTP, is designed to operate to at least 500 MHz. “Category 6 FTP cable may need to be redesigned to meet performance requirements to 500 MHz,” he says.


FTP cables feature a foil or braided shield with a non-conductive material on one side. Screened cabling blocks the reception and transmission of signals through the screened cable jacket. The drain wire runs adjacent to the conductive side of the overall screen. Proper installation practices vary by manufacturer.
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Pete Newman, director of marketing and customer service for Leviton Voice and Data Division, also notes the cable’s technical issues and UTP’s history of evolution. “I don’t believe shielded Category 6 solutions will overtake UTP in the market,” says Newman.

He explains that shielded cable is difficult to install, and most contractors are untrained and inexperienced in these installations. He also believes that manufacturers will develop UTP solutions for 10-Gbit Ethernet that will be able to provide protection from ANEXT.

Newman says such UTP cables will eventually approach the OD of Category 6 FTP, and he believes it is only a matter of time before these solutions come to market, since research and development teams are working on them now. The new UTP cables, Newman adds, which would be more installer-friendly, would prove more attractive than the shielded Category 6 solutions.

But not all contractors are thrilled about the prospects of working with Category 6 FTP cable, which can be challenging to terminate, ground and bond. They say part of the problem with deploying shielded cable is that there is no set standard for its installation. William Boyd, project manager for Indianapolis Electric Co. Inc. Commercial & Industrial Wiring, for example, installed shielded copper cable about a year ago for an enterprise end user in Indianapolis. He says the installation was challenging because he found it difficult to ground the cable, which caused a current flow problem.

“Grounding and bonding problems crop up,” says Boyd.

The ANEXT advantage

Still, many argue that Category 6 FTP cable’s advantages can’t be denied. The most important of these is the immunity to ANEXT. BICSI’s Shaver says manufacturers have been trying to reduce ANEXT in Augmented Category 6 cables by expanding the size of patch panels, creating more space and, therefore, distance between cables. But he says it is a strategy that only causes a waste of unutilized space: “When they start spreading out the patch panels to make the cable work, it just doesn’t make sense.”

Until now, shielded cable has also, in some ways, been subject to FUD (fear, uncertainty and doubt). But Rybinski says that is expected to change. “Now with 10-Gigabit Ethernet, it will make sense for our customers to put this through their networks,” she says.

Another important advantage is Category 6 FTP’s OD. Shaver notes that Augmented Category 6 UTP cable is thicker than Category 6 FTP cable. The OD for Augmented Category 6 UTP cable is at least .315 inches, which can limit the amount of cable that can be put into pathways and spaces. Even pulling two to three Augmented Category 6 UTP cables through a ¾-inch conduit, Shaver says, can become an issue.

But fill ratios will change when Category 6 FTP cable is installed in conduits and pathways. For example, consider that the shielded version of Mohawk’s Category 6 cable would have a smaller OD than the GigaLAN 10 product: the shielded Category 6 version’s OD is 0.251 inches, while the UTP Augmented Category 6 version has an OD of 0.315 inches. This difference lets you pull in a high-density bundle that will not be effected by ANEXT.

“Cable size is a significant issue in the design of a cabling system,” says Berk-Tek’s Harpel. “Your (Augmented Category 6) UTP cable is so large that it can really limit the number of cables you can put in pathways and spaces.”

Mass-market appeal?

But will Category 6 FTP cable, in the end, represent a strong market trend or simply a niche for the U.S. market?

As far as enterprise end users go, Harpel says the high cost of shielded cable, coupled with the market focus on UTP cable, will make Category 6 FTP cable a less desirable option for many installations. Mohawk’s Niemiera also remains skeptical, noting that the market is firmly entrenched in UTP cable: “I don’t see the market going to a shielded design.”

Harpel also believes the shielded Category 6 product will be more of a niche product for government and military installations and casinos. In some cases, it will be attractive to universities or enterprise end users who will need it for data center applications. They are also end users who generally have smaller cable pathways and who could benefit from the smaller OD of Category 6 FTP.

But even if the shielded Category 6 solutions won’t overtake UTP in the market, Newman says, “Manufacturers need to offer products for niche installations that require shielding for reasons other than alien crosstalk performance. Secure communications in some government installations is an example. Even if a government project requires shielding for only 5 or 10% of the drops, they still require a complete solution, and we have to offer it.”


Coming to terms with terms

The term “shielded cable” can refer to a number of different types of cable, and the nomenclature can be confusing.

The acronym STP can be used to refer to any twisted pair cabling that contains shielding. STP, however, should not be confused with screened twisted pair (ScTP) or foil twisted-pair (FTP), which are used with Ethernet networks and designed with pairs surrounded by a single foil or braided screen.

The acronyms ScTP and FTP are often used interchangeably. ScTP’s construction typically consists of four twisted pairs of solid copper with a foil laminate shield, and at least one tinned copper drain wire within a thermoplastic jacket. An FTP cable is a four-pair cable that is basically a shielded version of the category UTP cables.

A pairs-in-metal foil cable (PiMF) includes pairs that are individually shielded, and is sometimes referred to as double shield twisted-pair cable (SSTP). PiMF cable usually (but not always) contains an overall shield in addition to the shield on each pair.-BM

BRIAN MILLIGAN is senior editor for Cabling Installation & Maintenance.

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