There are municipalities where the Authority Having Jurisdiction (AHJ) requires that all low-voltage cabling be installed in conduit. Chicago and Las Vegas are a few prominent examples. This is a fire and life-safety requirement and does not take into consideration the performance of the cabling once installed. That is our job.
If you are designing systems for or installing high-performance low-voltage cabling in conduits and using cable-pulling lubricants, heads up!
There is a known problem, and for lack of a better term, I am calling it the “Wet Link Phenomena.”Longer links of unshielded twisted-pair higher-performance cabling installed in conduits using cable-pulling lubricants are failing attenuation, return-loss and insertion-loss testing.
As I understand it, the signal loss appears to be caused by radio-frequency-induced heating of the residual water (in the cable-pulling lubricant on the outside of the cable jacket) that is causing the “Wet Link Phenomena.”
This problem is not new; there have been warnings on cable manufacturers’ Web sites since 2003. The “Wet Link Phenomena” is not isolated to any one or group of manufacturers’ products, but is common to all unshielded twisted-pair cables. But the effect on performance is now more apparent with more use of higher-performance Category 6 and 6A cables because of their extended frequency range.
Shielded twisted-pair and fiber cabling are not experiencing the problem.
Cable manufacturers’ position
Cable manufacturers are aware of the situation and are taking the “not my problem” stance. And actually, it is not.
Here is why: First, TIA-568-B.1 cautions us to avoid excessive pull tension when installing cables. Then TIA-569-B, Subclause 8.1, General, states, “Building pathways shall be installed in ‘dry’ locations that protect cables from moisture levels that are beyond the intended operating range of ‘inside’ premises cable.” And finally, a note in TIA-569-B, Clause 8, Tenant Building Pathways, Subclause 220.127.116.11 Pull Tension, suggests using cable-pulling lubricants to reduce cable-pulling tensions, but cautions us to consider compatibility with cable jacket composition, safety, lubricity, adherence, stability, and drying speed when selecting a cable-pulling lubricant.
Sort of cryptic, but the message here is: Don’t pour water or anything that is going to eat through the cable jacket on CMR and CMP cable.
Types of cable-pulling lubricants
There are currently four types of cable-pulling lubricants commercially available. The majority of the products sold are in the first two types:
1. Wax-based lubricants are stabilized water-in-oil emulsions. They have very low coefficients of friction and are great for very long (over 1,000 ft.) cable pulls. But the time required for 100% evaporation of the water component is also very long. Most of us know this type of lubricant as “Yellow 77.”
2. Polymer-based lubricants are gel-matrix compounds containing varying amounts of acrylic acid polymers, along with various hydrocarbon lubricant systems; for example glycols, quaternaries, detergents, and soaps. Cold-weather-rated polymer-based lubricants are heavily loaded with propylene (or ethylene) glycol, which, while giving them the ability to remain liquid in low temperatures, also translates to very long drying times. There are also some cable-pulling lubricants with very fast drying times.
3. Talc-based lubricants are simply micro-pulverized talc (magnesium silicate hydroxide), sometimes with a small amount of desiccant (typically, cornstarch) added. Their primary claim to fame is that they are not liquid in nature and are totally water-free. But they also have the highest coefficient of friction of any cable-pulling lubricant system available.
4. Silicone-based lubricants are 100% silicone liquid/gels, typically refined to a syrup-like consistency. They are totally water-free and exhibit extremely low coefficients of friction. But they are not compatible with some cable jacketing materials, particularly polyolefin and vinyl chloride.
Good for the environment, but...
Cable-pulling lubricant manufacturers are also aware of the problem. Of the multitude of cable-pulling lubricant manufacturers’ sites that I visited recently, each claimed that their polymer-based lubricants were compatible with all types of telecommunications cables.
Environmentally safe, non-toxic, non-flammable non-corrosive-you could practically bathe in this stuff. And after reviewing the Material Safety Data Sheets for these products, that makes sense. You see, the primary ingredient-in some cases, 95% of the product-is water. OK for the environment and the installer, but not for CMR and CMP cable until the water evaporates.
Many low-voltage cabling contractors are not aware of the problem; hence, this article being written now.
As I see it, the primary focus of low-voltage cabling contractors is the same as for all of us-to get paid for the service that we perform. To do this, many contracts require that the low-voltage cabling contractor deliver a cabling system with a warranty provided by the cabling manufacturer. To get the cabling manufacturer to provide the warranty, the cabling system has to be proven to meet warranty requirements; usually this mean to pass TIA permanent link field-testing after installation.
Over time, as the cable-pulling lubricant dries, the “Wet Link Phenomena” will go away. But how long that will take will depend on the type and amount of lubricant used and the air flow through the conduit. The actual quantity of lubricant used depends on the difficulty and length of the pull and the conduit size.
Translation: As little as a quart or as much as five gallons could be present in a conduit run. And that is going to take a while to evaporate.
This puts the low-voltage cabling contractor in a “damned if you do and damned if you don’t” situation. Using no cable-pulling lubricant risks cable damage and test failure, while use of cable-pulling lubricant can mean weeks or months before the cable dries out sufficiently to be tested and used.
Next month, I plan to explain why this is happening and provide an update on progress being made toward a solution.
Concerns about pulling tension in horizontal pathways are not new. Here is an excerpted Q&A concerning pull tension, fiber-optic cable, and innerduct from an “Ask Donna” column that ran in January 1998. Although much has changed in the nearly nine years since this correspondence first ran (including some of the nomenclature), the essential points remain relevant.
Q: Should fiber-optic horizontal cable be installed in innerduct? In the environment in question, plenum fiber-optic cable is being installed between a data closet and a classroom.
Some of my colleagues favor installing innerduct in the route to protect the fiber and for ease of placement. They cite BICSI’s Cabling Installation Manual. Others argue that a fiber-optic cable properly routed through a ceiling cable-support system is as secure as the innerduct system.
The added expense of a double plenum hit-plenum innerduct and plenum fiber cable-is not justified because the job is not a multi-tenant environment in which each customer uses a different vendor and installs different cable.
A:I believe that prudent use of short pieces of plenum optical-fiber raceway in ducts, plenums, or other spaces used for environmental air is good cable-management design; however, providing a listed plenum optical-fiber raceway from the telecommunications closet to the work-area outlet will continue to make fiber-to-the-desk unnecessarily cost-prohibitive. At [a higher] pulling tension, optical-fiber cable has always been a more robust medium than the more widely deployed unshielded twisted-pair cable, at 25-lbf pulling tension.
Although BICSI’s Cabling Installation Manual is a good place to start, it is not an industry standard. It did not go through the same industry-wide balloting and comment resolution process that the standards of the Telecommunications Industry Association are held to.
DONNA BALLAST is BICSI’s standards representative, and a BICSI registered communications distribution designer (RCDD). Send your question to Donna at: email@example.com