Exposing under-floor cable

On a project I am working on, a 600-pair, PE-rated outside plant cable is being installed between two buildings. One end is to be terminated in the main computer room, which has a raised floor (plenum air return)

May 1st, 2001
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Q: On a project I am working on, a 600-pair, PE-rated outside plant cable is being installed between two buildings. One end is to be terminated in the main computer room, which has a raised floor (plenum air return). The consultant on the job wants to run the PE cable exposed under the floor and terminate on a backboard in the computer room. Is the consultant correct when he said they could run the cable (less than 50 ft) exposed? Please give me your opinion and supporting references.
Larry Gillis, RCDD
MasterLink Communications Corp.
Gilbert, Arizona

A: Polyethylene (PE) is tough stuff- resistant to water, acids, alkalis, and most solvents. Polyethylene is the plastic we see most in daily life, from grocery bags, shower curtains, shampoo bottles, children's toys, drinking glasses, pipes, and yes, even to insulation for wire and cable

But it is my personal opinion that PE cable under a raised floor anywhere is not a good idea, especially in a data center. Polyethylene burns like a candle and creates lots of sooty smoke. Any data center equipment that survived the fire event would certainly fall victim to the smoke. With the exception of the carbon black added to outside plant cable jacketing, the cable jacketing and plastic milk jugs are both made from the same material-High Density Polyethylene (HDPE). If you want a preview of what HDPE produces during a fire event, burn a milk jug in a shinny new metal garbage can. Then ask the consultant how many milk jugs there are in 50 ft of cable?

I know this sounds weird, but whether or not the consultant's proposal is in compliance with the National Electrical Code (1999) depends entirely on how far it is between the two buildings, how tall the buildings are, and how many thunderstorms they see in a year. I will attempt to explain.

Article 800-50 says: "Communications wires and cables installed as wiring within buildings shall be listed as being suitable for the purpose..."

Article 800-50 Exception No. 3 says: "Listing and marking shall not be required where the length of the cable within the building, measured from its point of entrance, does not exceed 50 ft (15.2 m) and the cable enters the building from the outside and is terminated in an enclosure or on a listed primary protector." Notably absent from Table 800-50, PE.

Article 800-50 Exception No. 3 FPN (Fine Print Note) No. 2 attempts to explain that what Article 800-50 Exception No. 3 gives-50 ft of unlisted outside plant cable, Section 800-30 can take away.

Article 800-30 requires a listed primary protector on each pair of a cable that could accidentally come in contact with electric light or power conductors operating at over 300 V to ground. No chance? What about lightning exposure?

Article 800-30 also requires a listed primary protector on each pair of a cable that is exposed to lightning. Interbuilding cables are considered to have a lightning exposure unless installed in large metropolitan areas where buildings are close together and sufficiently tall to intercept lightning, or where cable runs between the buildings are 140 ft (42.7 m) or shorter, or the site has an average of five or fewer thunderstorm days per year and earth resistivity of less than 100 ohm-meters.

So, if your site is required to have primary protectors, then Article 800-30 requires that they "shall be located in, on, or immediately adjacent to the structure or building served and as close as practicable to the point at which the exposed conductors enter or attach."

Article 800-30 also defines exactly "the point": "For purposes of this section, the point at which the exposed conductors enter shall be considered to be the point of emergence through an exterior wall, a concrete floor slab, or from a rigid metal conduit or an intermediate metal conduit..."

Game over.


Is Cat 5 really dead?

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Q: I attended the Orlando BICSI conference. One of the sessions mentioned that Category 5 cabling will become obsolete. Can you clarify what is meant by Cat 5 cabling being classified as a non-standards-compliant product? I assume that many of the major cable manufacturers have ceased manufacturing Cat 5.
Dan Holstein, RCDD
Multimedia Distribution Solutions
Cleveland OH

A: Yes, I too have heard the cry, Cat 5 is dead, long live Cat 5E. Which, will no doubt be replaced by Cat 5E is dead, we finally finished Cat 6. But that is another issue entirely.

The following is an exact quote from ANSI/TIA/EIA-568-B.1 dated March 2001:

The majority of the text in clause 4.5 has been around since ANSI EIA/TIA-568 was published in July 1991. The choices back then were four-pair 100-ohm UTP for the "one telecommunications outlet/connector," and the "other/second telecommunications outlet/connector" could be either four-pair 100-ohm UTP or two-pair 150-ohm or 50-ohm coaxial cabling.

When ANSI/TIA/EIA-568-A was published in October 1995, the text in clause 4.5 changed very little, but the media choices changed a lot. The four-pair 100-ohm UTP for the "one telecommunications outlet/connector" now had to be Category 3 or higher, and the "other/second telecommunications outlet/connector" now had to be four-pair 100-ohm UTP (Category 5 recommended,) or two-pair 150-ohm, or two-fiber or 62.5/125 micron optical-fiber cable. 50-ohm coaxial cable (from the TIA-568-1991 edition) was banished to informative Annex G, to quietly fade away.

In ANSI/TIA/EIA-568-B, not only do the choices change again, but it appears that the committee has attempted to control not only your media choice for the first and second outlet/connectors but for all that you choose to install. It could be argued (most likely by a salesman sitting across your desk from you) that the subtle addition of the "(s)" to the previous "other/second telecommunications outlet/connector" now explicitly prohibits the use of any media not listed in clause 4.5.

From my perspective, this is not so. Your use of Category 5 for the first outlet-Category 5 is higher than Category 3-or your use of singlemode optical fiber, or even Category 5 for any additions to the first and second outlets complies with "The two telecommunications outlet/connectors shall be configured..."

Like 50-ohm coax cable, Category 5 (from the TIA-568-A-1995 edition) has also been banished-to informative Annex D-to quietly fade away.

Your assumption is correct that some manufacturers no longer produce Category 5 components. But with few exceptions, the Category 5 links that I have seen have passed when tested as Category 5E permanent links. Those that did not were reterminated and then passed as Category 5E. I am currently specifying installation of Category 5E permanent links for all new installations as recommended by IEEE to support 1000Base-T.

Donna Ballast is a communications analyst at The University of Texas at Austin and a BICSI registered communications distribution designer (RCDD). Questions can be sent to her at Cabling Installation & Maintenance or at PO Drawer 7580, The University of Texas, Austin, TX 78713; e-mail: ballast@utexas.edu.


4.5 Choosing types of cabling

This standard recognizes the importance of both voice and data telecommunications in a commercial building. A minimum of two telecommunications outlet/connectors shall be provided for each individual work area... One telecommunications outlet/connector may be associated with voice and the other with data. Consideration should be given to installing additional outlets/connectors based on present and projected needs.

The two telecommunications outlet/connectors shall be configured as:

a) One telecommunications outlet/connector shall be supported by a four-pair 100-ohm cable, Category 3 or higher (Category 5E recommended) as specified in ANSI/TIA/ EIA568B.2.

b) The other/second telecommunications outlet/connector(s) shall be supported by a minimum of one of the following horizontal media. This media choice should be based on present and projected needs.

1) Four-pair 100-ohm Category 5E cable as specified in ANSI/TIA/EIA568B.2.

2) Two-fiber multimode optical fiber cable, either 62.5/125 m or 50/125 m as specified in ANSI/TIA/EIA568B.3

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