Wet link progress report

Nov. 1, 2006
When it comes to the “wet link phenomena” topic, it appears that everyone is currently “in the lab.

When it comes to the “wet link phenomena” topic, it appears that everyone is currently “in the lab.” The pulling-lubricant manufacturers are busy inventing and cable manufacturers are busy testing. No one is talking. At least, not yet.

But there has been some action on the matter. In June, TR-42.3 Commercial Building Telecommunications Pathways and Spaces established a task group to investigate conduit-fill issues. In October, TR-42.7 Telecommunications Copper Cabling Systems announced they are initiating an investigation regarding the performance effects of pulling lubricants under controlled conditions, and they are asking for our help with this investigation. TR-42.7 is seeking the following data points on failing links: Type of conduit (EMT, ENT, IMC); size of conduit, number of cables, and their diameters; length between pull points; quantity and radius of bends between pull points; type of cable(s) (Category 5e, 6, 6A); sheath type (CMP, CMR); cable configurations during the pull (bundled, one at a time, several at a time); quantity and type of pulling lubricant used; permanent-link test data; the number of cables in the conduit that failed.

If you are experiencing problems that you believe are related to the use of cable-pulling lubricants, please forward your information to Herb Congdon, chair, TR-42 at: [email protected].

Further updates will be provided as information becomes available.

Changing times

While the manufacturers are all in “CYA” mode, we should address what changes we need to make in the systems’ design to avoid this “wet link phenomena” problem in the future.

So, which design comes first, the cabling system or the conduit system that supports it? Logically, the cabling system. Once the quantity and type of cables required at each outlet location is determined, then the conduit system runs should be sized accordingly. For example, two Category 6A cables from a telecommunications room to an outlet location would require a Trade Size 1 (1-inch) conduit based on the following from the 2005 National Electrical Code:

Article 358 Electrical Metallic Tubing: Type EMT covers the use, installation, and construction specifications for electrical metallic tubing (EMT) and associated fittings.

Section 358.22 Number of Conductors states, “The number of conductors shall not exceed that permitted by the percentage fill specified in Table 1, Chapter 9. Cables shall be permitted to be installed where such use is not prohibited by the respective cable articles. The number of cables shall not exceed the allowable percentage fill specified in Table 1, Chapter 9.”

• Chapter 9, Table 1 Percent of Cross Section of Conduit and Tubing for Conductors allows 53 percent fill for one conductor, 31 percent fill for two conductors, and 40 percent fill for more than two conductors.

Now let’s talk conduit:

• Section 358.24 Bends-How Made states, “Bends shall be made so that the tubing is not damaged and the internal diameter of the tubing is not effectively reduced. The radius of the curve of any field bend to the centerline of the tubing shall not be less than shown in Table 2, Chapter 2 for one-shot and full shoe benders.”

• Section 358.26 Bends-Number in One Run states, “There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points, for example, conduit bodies and boxes.”

TIA-569-B limits the bends to two 90-degree bends and 100 feet maximum length between pulling points. The difference between NEC 2005 requirements and TIA-569-B requirements are primarily the number and severity of bends and length of conduit between the pulling points along the conduit run. This is huge.

Good, better, best

In the “good, better, best” of conduit system design for telecommunications cabling, NEC presents the “good” set of design requirements and TIA the “better” set; the “best” would be using the most stringent of both and designing for additional cables to be placed in the future. But that is going to be a tough sell due to the increase in cost of the larger conduits. Translation: The NEC “good” is what the installer sees most often.

Most of the “wet link” problems reported so far are with conduit runs that are less than the “good” required within the NEC today. But unshielded twisted-pair cables are continuing to get fatter as we step through the categories, so the problem is only going to get worse. Looks like this one is up to us to resolve, at least for now.

The TIA generic cabling systems that we install fall under different rules within the NEC, depending on the applications that the cables are being used for at any given time. For us to design these “generic” systems within NEC requirements, we need to perform a line-by-line comparison of the requirements in Article 725 Section I General and Section III Class 2 and Class 3 Circuits, as well as Article 800 Communications Systems-then apply the most restrictive.

So, let us begin by using NEC 2005. Section 90-3 states, “Chapter 8 covers communications systems and is not subject to the requirements of Chapters 1 through 7 except where the requirements are ... referenced in Chapter 8.”

• Section 725-3 Other Articles states, “Circuit and equipment shall comply with the articles or sections listed in 725.3(A) through 725.3(G). Only those sections of Article 300 referenced in this article shall apply to Class 1, Class 2, and Class 3 circuits.”

• Section 725-3-A Number and Size of Conductors in Raceway states, “Section 300.17.”

• Section 300.17 Number and Size of Conductors in Raceway states, “The number and size of conductors in any raceway shall not be more than will permit dissipation of the heat and ready installation or withdrawal of the conductors without damage to the conductors or their insulation.”

Article 800 makes no reference to Section 300.17, so we need to default to the requirements in Article 725 Section I.

Now, let’s look at Article 310 Conductors for General Wiring, Section 310.9 Corrosive Conditions, which states, “Conductors exposed to oils, greases, vapors, gases, fumes, liquids, or other substances having a deleterious effect on the conductor or insulation shall be of a type suitable for the application.”

Is there a resolution?

Doesn’t that prohibit the use of any type of cable-pulling compound that negatively affects the performance of a data cable? No, because Article 310 is not called out as applicable in either the General or the Class 2 and Class 3 sections-only in Class 1 of Article 725, and Article 800 makes no reference to Section 310.

Now, having read NEC 2005 sections 300.17 and 310.9, do you agree that the requirements we need to resolve this problem are in the NEC, but are just not currently applicable to our cabling?

DONNA BALLAST is BICSI’s standards representative, and a BICSI registered communications distribution designer (RCDD). Send your question to Donna at: [email protected]

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