Q: Is there a recommended or preferred approach to recabling an existing network patch bay? The objective is to clean up an inherited environment and make everything neat and tidy. Is the best approach to simply document the existing connections and then pull everything out and start fresh?
A: If you can't take the entire bay out of service but are upgrading the hardware-and have the space-set in one additional equipment rack. Install the new hardware and patch-cord managers in the new equipment rack and patch, which will allow you to clean up the mess without having the entire network disabled. If you are not upgrading the hardware, you can use the same approach: Install only one additional hub or switch in the new equipment rack and patch, then move another hub or switch and patch.
Be prepared for a long weekend followed by a few trouble calls on Monday. Don't make things too tidy. If you pack the cords too tightly, you will create performance problems. If you make it too difficult to move a patch cord, users will simply remove the plug at one or both ends, leaving the cord in the wire manager, and install a new patch cable.
The most important product of this exercise will be the cable-patching records that you create. Get them into a database. There are many cable-management software packages available, but for a small network, even a spreadsheet is better than no records at all.
Containing dust at the work site
Q: I once saw an ad for an easy-to-assemble, temporary plastic barrier to keep dust and contaminants in the work area from entering the rest of the office or clinical space. I remember telescoping poles and clips for the ceiling that one person could assemble. Do you know where I can find such a system?
Cooley Dickinson Hospital
A: Does QuickProp ring a bell? QuickProp, designed for repeated use, is a quick and quiet way to erect a construction barrier.
QuickProp is made from aluminum poles that can extend from 5 ft 7 inches to 16 ft 6 inches high, which can support up to 9-mil polyethylene film. Installation can be done quietly in only a few minutes without any tools or special knowledge.
The rubber floor and ceiling pads leave no soil marks, making the product suitable for use with suspended ceilings (see www.pro-tect.com, for more information).
Application is easy:
- Pull out rivet from top suction pad and place pad on the top of pole.
- Pierce through the edge of film with the rivet, securing it into the hole at the center of the top suction pad.
- Attach bottom suction pad to bottom pole.
- Release thumbscrew tension and extend pole, with film attached to top, until both suction pads are compressed between floor and ceiling. Tighten thumbscrew while firmly holding poles at the joint to maintain compression.
- To vertically secure the film at each pole, the film can be clipped to the pole with plastic clips, which are included for each pole.
How much weight can ceilings take?
Q: My experience with suspended ceilings leads me to believe that the ceiling mentioned in your December 1999 column, "It's standards-compliant, but is it safe?" (page 10), collapsed due to other factors. Ceiling-mounted fixtures include lighting fixtures, smoke detectors, horns, strobes, cameras, HVAC vents, and anything else that the architect doesn't want on the walls. Ceiling grid systems are available in several grades based on their ability to hold the weight of ceiling-mounted fixtures. These range from residential grades, which can barely hold the weight of the tiles, to commercial systems that can support several hundred pounds if properly supported.
The grid in your example most likely collapsed due to one or more of the following factors: improper support spacing for the fixture loading (manufacturers will specify the support spacing required to support rated fixture loads); a nonload-bearing grid system was installed; and fixtures mounted in the ceiling exceeded the weight limitations of the system.
The National Electrical Code allows fixtures to be supported by the grid, but several problems with grid installation due to these factors has prompted some local electrical inspectors to require that lighting fixtures be supported independent of the grid system. I find it hard to believe that the system cabling alone caused this failure.
Daniel L. Pohnert, PE CEM
Reynolds, Smith and Hills Inc.
A: In the December 1999 example, the ceiling grid was not supporting the cabling. Rather, the cabling was secured to the ceiling support wires. Under the weight of the telecommunications cabling, the anchors pulled out of the deck.
According to the product catalogs, 1,000 ft of Category 5 cable weighs about 25 lbs, or 0.025 lb per foot. If we support the cable every 4 ft on existing ceiling support wires, that's 0.1 lb per cable on the hanger. This weight multiplied by three cables per work area results in 0.3 lb per work area on the hanger. This measurement is not much compared to the weight of grid-supported light fixtures-until you approach the entrance to the equipment room, where the cables really start to pile up.
The TIA/EIA-569A standard offers guidance for sizing equipment rooms to support up to 1,200 work areas. With a minimum of one cable for voice and two cables for data per work area, that can equal more than 300 additional pounds of cabling added to all the additional fixtures that Daniel Pohnert mentions.
In a perfect world, there is only one generation of telecommunications cabling in the ceiling of a building. In the real world, there can exist an entire genealogy dating back to the commissioning of the building or the last fire. While clients will pay to have new cabling installed, convincing them that the old cabling should be removed is next to impossible without bringing in the fire marshal.
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; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: firstname.lastname@example.org.