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CABLE TRAYS CHAPTER 3: COMMUNICATION SITE BUILDING DESIGN AND INSTALLATION 3.10 CABLE TRAYS Minimizing the overall distances of the DC power system and the grounding layout should be a priority. The control room housing the switch terminals should be isolated from the rest of the equipment to provide noise reduction for those continually working in this environment. This room should also be configured as an Isolated Ground Zone (IGZ). This section provides requirements and installation guidelines for cable trays. Cable trays should be used to support communications cabling within buildings and shelters. Cable trays provide proper support of cables between cabinets, relay racks and bays of equipment and help maintain adequate separation between the cable groups. The orderly separation and support of cable also simplifies maintenance. Cable management over relay racks and equipment cabinets can be accomplished by utilizing cable tray systems. These tray systems are designed to provide support, routing, parallel separation and securing of wires and cables as defined in “Cabling Requirements for Cable Trays or Ladders” on page 9-14. As defined in NFPA 70-2005, Article 392, a cable tray or tray system is a unit or assembly of units or sections and associated fittings forming a rigid structural system used to securely fasten or support cables and raceways. NOTE: Aluminum ladders designed for climbing shall not be used as cable trays. 3.10.1 CABLE TRAY SELECTION Two types of overhead cable tray systems which are suitable for use as cable support are: • Steel stringer style ladder • Aluminum or steel ladder style cable tray Steel stringer style ladders come in various designs and styles. Typically they are available in Cchannel, tubular and solid bar in painted or yellow zinc dichromate finishes. Stringers are typically 38.1 mm (1.5 in.) to 51 mm (2 in.) in depth, and vary in length. Rungs should be spaced at least 229 mm (9 in.) apart. Simple hardware is used to make “T” and cross connections. “J-bolts” (threaded, formed metal rods bent into a “J” shape) shall not be used as fasteners for cable trays. These rods typically deform when stressed, possibly allowing cable trays to drop. Captive hardware such as threaded bolt, washers, and nuts are recommended. Aluminum or steel cable tray systems also come in various designs and styles such as ventilated trough, solid trough and ladder type with “I” beam or C-channel siderails. The most practical is the ladder type. The major difference between the stringer style ladders and tray systems is that a tray has a siderail or wall height from 102 mm (4 in.) to 178 mm (7 in.). This load depth may be desirable for large bundles of cables or transmission line routing. The siderail height affects overall rack to cable tray to ceiling dimension restrictions as outlined in this chapter. A rung spacing of 229 mm (9 in.) is also recommended for this tray type. This type of tray system requires prefabricated Ts, bends, crosses and reducers, which must be factored into the system design. 3-18 68P81089E50-B 9/1/05
STANDARDS AND GUIDELINES FOR COMMUNICATION SITES CABLE TRAYS Both types of tray are available in widths ranging from 102 mm (4 in.) to 1.06 m (42 in.). Typically, widths of 457 mm (18 in.) and 610 mm (24 in.) are used. Stacking of 457 mm (18 in.) wide trays is allowed, but ceiling height requirements and clearances shall be adhered to. Cable support system design shall provide for maintaining a spacing of 457 mm (18 in.) between trays. The overall sizes of cables, numbers of cable, and number of cable groups required in a run shall be considered when specifying tray width. Account for a minimum of 152.4 mm (6 in.) loss of width for cable group spacing in itself. NOTE: In all cases the width of the cable tray shall not be less than 457 mm (18 in.) and is recommended to be 610 mm (24 in.). 3.10.2 CABLE MANAGEMENT UNDER RAISED FLOORS NOTE: Do not mix aluminum and steel tray types at a facility installation. For wire management under raised computer floors, a welded wire mesh cable tray system is recommended. This type of tray system can be mounted to, or suspended from, raised floor pedestals or sub flooring. This tray system typically consists of high strength steel wire in the form of a 50 x 100 mm (2 x 4 in.) mesh. The finishes can be electro-plated zinc galvanized or stainless steel that are suitable for all environments. Bends can be fashioned by cutting the mesh with a bolt cutting tool and simple hardware connections to the wire mesh. Manufacturers can supply bonding terminations and outboard ground cable supports for proper tray system grounding. 3.10.3 WIRE-MESH CABLE TRAYS In general, observe the following considerations when in selecting cable trays. See “Cable Trays” on page 5-45 for proper cable tray grounding practices. All trays whether above racks or below raised floors require the same grounding practices. • Noting the amount of cables to be supported by each run, cable tray width shall be selected to provide 50.8 mm (2 in.) minimum separation between cables or cable groups. 457 mm (18 in.) trays or double-deck ladders may have to used in some cases. • Steel stringer and steel tray systems shall utilize an extended post to attached grounding conductors. This post should extend 102 mm (4 in.) to 152.4 mm (6 in.) either horizontally or vertically from the siderail of the tray, with no less than 457 mm (18 in.) of spacing between posts. • If AC power cables are to be run in cable trays, cable separation and special considerations shall be maintained. • The size, weight, and projected expansion of the system shall be considered to ensure proper tray usage. The “hang”' test shall not be used. • The number and function of conductors to be placed within a cable tray shall be considered before procuring cable trays. • It is recommended that only cable trays specifically designed for communications purposes be used (as opposed to standard electrical cable trays). 68P81089E50-B 9/1/05 3-19
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© 2005 MOTOROLA, INC. ALL RIGHTS R
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TABLE OF CONTENTS Chapter 1. Introd
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STANDARDS AND GUIDELINES FOR COMMUN
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CHAPTER 1 INTRODUCTION 1 This manua
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CHAPTER 5 INTERNAL GROUNDING (EARTH
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CHAPTER 6 POWER SOURCES 6 6.1 LOCKO
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CHAPTER 7 SURGE PROTECTIVE DEVICES
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CHAPTER 8 MINIMIZING SITE INTERFERE
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CHAPTER 9 EQUIPMENT INSTALLATION 9
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APPENDIX A ELECTROMAGNETIC ENERGY I
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APPENDIX B SOIL RESISTIVITY MEASURE
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APPENDIX C PROTECTING AGAINST ELECT
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APPENDIX D GROUNDING (EARTHING) ELE
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APPENDIX E GENERAL CONVERSIONS AND
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APPENDIX F R56 COMPLIANCE CHECKLIST
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I NDEX Index Index AC power cabling
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