Telecommunications Cabling and Electronics Specifications Guidelines


Contact: Ron Olton

Horizontal Raceways

The horizontal raceway system is the most important link in the entire network chain. There is more invested and involved in this segment of the network than in any other. The horizontal raceway connects the individual workstation with the FLOOR WIRING CLOSET. Individual runs of this raceway may appear to be of minor significance but if an entire building or campus is inadequately equipped with raceway the penalty may be the inability to take advantage of technological advancements.

GENERAL:
The raceway must be designed to carry all types of telecommunication cables known to be required today. These include facilities for voice, data, video, telemetry, etc. The types of cable known to be needed today consist of copper paired cable, coaxial -- twin axial cable, and fiber optic cables. Provision must be made to allow for growth in numbers of users, as well as types of media as new applications evolve.

It is important to point out that in a community college campus environment there are a very large number of relocations and changes taking place on an ongoing basis. Raceways should not be designed for the planned, initial use of an area only. They should be sized for the growth expected in the next 10 to 15 years.

TYPES OF SYSTEM:
  1. Under floor. This type of raceway is not the preferred method to use. Its’ use should be limited to those locations where a better method cannot be used.
  2. Cellular Floors. This type of raceway is not the preferred method to use. Its use should be limited to those locations where a better method cannot be used.
  3. Unlimited Access Floors. This type of system is usually found in a computer room where a large number of cables are required within the room, and beyond the room to a FWC. The initial cost and noise properties of this type floor restrict its use to special applications.
  4. Under Carpet. Use of this type of system should be avoided in community college buildings. Its use should be limited to those locations where it is absolutely necessary.
  5. Ceiling Access. This is a commonly used distribution system in community college buildings. It is frequently incorporated with two other methods of distribution, utility columns and conduit. Care must be exercised when this method is used to be certain that accesses are provided through walls extending above the ceiling, that the ceiling is an easy access ceiling (lay in type) and no more than 11 feet above the floor. If the ceiling space is used as an airway for the HVAC system, plenum cable is required. This increases the cost of installation and changes.
  6. Utility Columns. These devices are becoming more popular. When utility columns (power poles) are proposed, care must be taken to provide adequate space for the multiple cables that must be placed in the column. More space is commonly required for the telephone cables than that needed for power. Space for terminations (jacks) is also greater than customarily provided in the column. Refer to the portion of this section dealing with raceway sizing to assist in sizing utility columns.
  7. Perimeter Raceways. Use of this type of raceway may be appropriate when most of the workstations will be along the walls. Care must be taken when using this raceway that corner radii (both inside and outside) are not too small for fiber cables. Refer to the portion of this section specifying minimum bend radii. As with all raceways particular attention must be paid to the size required for telephone cables and to facilitate the larger termination device (jack).
  8. Trays--Racks. Cable trays or racks should only be used in ceilings or inside WCs where security and protection are not an issue. With this type of raceway, consideration should be given to the advantages of solid bottoms and sides in the trays to minimize the exposure to electromagnetic fields present around lighting fixtures and HVAC motors and controls.
  9. Interstud. This method requires wiring to be installed during construction of the building or by fishing the walls after construction is completed. This method affords no security or protection to the cables. The use of delicate fiber cables to the work station prevent the use of this method since fiber cables cannot withstand the rigors and strains of pulling through wall cavities.
  10. Exposed Wiring. While exposed wiring is permitted by the NEC and all other standards presently in effect, this method is not to be used in new or remodeled buildings at community colleges. This method affords neither protection nor security.
  11. Conduit. Conduit in its various forms is the most commonly used raceway in community college buildings. Conduit may be metal tubing, steel pipe, PVC pipe, fiberglass pipe or plastic channel with a snap cover (wire mold). Flexible conduit should not be used. Conduit smaller that ¾-inch inside diameter should not be used.

The remainder of this section sets forth guidelines for the use of conduit raceways. Sections dealing with bends and size will be applicable to other raceway types, as well.

BENDS:
Conduit runs should contain no more than two 90 bends. If more bends are required, a pull box should be installed. A bend should not be accomplished within the box. Bends within pull boxes do not afford sufficient bending radius for fiber cables and some copper cables. The radius of bends in conduits should never be less than 10 times the diameter of the conduit. When using a molding type of conduit a series of angles will be intermixed with straight sections to accomplish a 90 bend.
RUNS:
Conduit runs may serve a maximum of two outlets (workstations). When this method is proposed, termination (junction) boxes must be of adequate size to allow a minimum 2 1/2-inch per 90 bend radius (five inches diameter for 180 bend) in the cables passing through to the last box.
SIZE:
Most all conduit runs will by necessity have two 90 bends, therefore can be 40 percent filled in compliance with the NEC. The current cable bundle that may be required to each workstation (jack) requires a minimum 9/16-inch envelope to enclose it. A minimum 1-inch conduit is required to serve a single workstation. A two inch conduit may be used to serve two or three workstations.
OUTLET BOXES:
Outlet boxes will be no smaller than 4-inches square. This size will accommodate outlets on the end of each conduit run, but due to the bending radius required for cables passing through the other boxes on the run, the boxes at pull through locations will need to be at least 5-inches wide if the conduits enter from the same side. See Figure 7-1.
CONDUIT ENTERING FWCS:
All ends of conduits must be reamed and bushed. If the conduit enters through the floor, it must be terminated 4-inches above the finished floor. If entering through a wall, it should be terminated as close as possible to the wall. 


                              FIGURE 7-1

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