March 1, 1999
Q: I am having a problem locating detailed information on the installation of high-pair-count (300-pair) copper cable in riser sleeves over 21 floors. Specifically, I am looking for information on sleeve loading and support. I believe we can get seven cables per vertical sleeve, and I anticipate using messenger wire from floor 48 to floor 28 to support the cables.

Q: I am having a problem locating detailed information on the installation of high-pair-count (300-pair) copper cable in riser sleeves over 21 floors. Specifically, I am looking for information on sleeve loading and support. I believe we can get seven cables per vertical sleeve, and I anticipate using messenger wire from floor 48 to floor 28 to support the cables.

I have several questions: Are seven cables too many? What would be the M rating of the messenger wire? How would the seven cables be attached to the messenger?

I am looking for references to do research on this but am running into dead ends. There is only a brief reference to any of this in bicsi`s Telecommunications Distribution Methods Manual, and the Cabling Installation Manual makes no reference at all to any messenger-type support.

Asterisk Enterprises Inc.

West Chester, PA

A: There are several factors in this equation, with the size and weight of the cable being the key. I assume from your description that you plan to place a 300-pair riser to each of seven floors in one vertical sleeve.

As for the research, let`s start with the easy part. Have you contacted a structural engineer to verify that all this weight--126 floor lengths of cable and seven floor lengths of strand--can be safely supported in this building? A typical 24 AWG riser cable weighs about 1.09 pounds/foot and is about 1.3 inches in diameter.

You will be required to firestop the floor penetrations. The qualified firestop system used will also be part of the "number of cables per vertical sleeve" equation--and then we need to factor in the diameter of the strand. If the sleeve is a typical 4-inch penetration, seven cables and the strand would exceed a 75% fill. On some manufacturers` intumescent firestop systems, the maximum cable fill can be as little as 20%. The maximum cable fill that I have seen allowed in a qualified firestop system is 40%. The solution is to use larger sleeves or use more of them.

For placement, the cable can be lowered by hand from the top floor using a cable shoe or cable sheave, or the cable can be pulled up to the top floor using an electric winch. Depending on the building construction, getting the cable reels to the 48th floor may not be an option. Before the strand is tensioned, insert tie wires into the lay of the strand at 3-foot intervals to support each cable sheath. Then, beginning at the top, secure each cable to the strand.

To determine the size of the strand, you have to know the distance between the floor slabs in the building. Multiply that distance by the number of floor lengths of cable to be supported, add the weight of the strand itself, and multiply the sum by 25%, assuming that you will be using less than a 16M strand.

For additional information, see at&t Practice 627-610-225. Contact at&t`s Customer Information Center at (800) 432-6600 for ordering information.

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