FAQ

No; walking on cable trays is not to be permitted. It violates the new version of NEMA standard VE-2, manufacturers marking and recommendations, and the intent of the NFPA70 Electrical Safety in Employee Work Practices. Walking on electrical equipment, conduits, cables or other electrical systems should also be avoided. In addition to the fall hazard, there is the risk of damage to equipment and possible contact with conductors.

Source: Cable Tray Institute (CTI)

Question: Can mechanical utility piping or tubing containing water or compressed air be installed in cable trays with electrical cables?

Answer: No. Cable trays are a support system for electrical cables, power, signal, and communication and optical fiber cables. NEC section 300.8 does not permit any tube, pipe, or equal for water, air gas, drainage, steam, or any service other than electrical in raceways or cable trays containing electrical conductors.

Question: I am in the process of establishing guidelines for raised floors in communications facilities and plan to mandate that all cabling under raised floors be installed on an appropriate type cable tray. Are you aware of any industry standard that may mandate the use of cable trays under raised floors, particularly, power and signal cables?

Answer: We are not aware of such industry standard, but cable trays offer significant advantages for this type of installation and in other computer, telecommunications, and power installations. The telecommunications industry is a very strong cable tray user.

Question: We are using ladder type cable trays at many of our facilities for telecommunications wiring. Do you have any information available for recommended installation clearances for this type of cable tray?

Answer: The NEC does not have a specific installation clearance, but indicates in section 392.6(H) that cable trays should be exposed and accessible. Telecommunications standard TIA/EIA-569 recommends a minimum of 12-inch access headroom above the cable tray.

Question: Are there required code grounding practices regarding cable tray used only for telephone cable? A contractor has just installed a new phone system at my location and he utilized cable trays in the switch room. I did not see any deliberate attempt to ground the system. Our existing cable tray system is heavy bonded and grounded. If this is a code violation, could you refer me to the publication?

Answer: Low energy systems may not be required to be grounded for shock or arcing, ut should be grounded for noise, lightening protection and electromagnetic interference. See CTI Technical Bulletin No. 15.and NEMA VE -2 section 4.7.

Question: Are there any requirements for separation and segregation of various types of cables (i.e. Power, instrumentation, signal, telecommunications, etc.) in cable tray systems?

Answer: Yes, there are NEC rules. Instrumentation, signal, and telecommunications cabling should be separated from power cabling. There are NEC requirements, but also for noise and electromagnetic pick-up from adjacent power cables. This can be accomplished by a separate cable tray system or by a divider within a cable tray.

NEC section 392.6(E)indicates that multiconductor cables rated 600 volts or less are permitted in the same cable tray, however, separation of power and control cables is necessary as indicated in other sections of the NEC and for cross-talk noise reasons. NEC section 392.6(F) provides the criteria for cables rated over 600 volts. The types of cables usually used in cable trays are type TC (article336), PLTC (article 725), ITC (article 727), MC (article 336) and Communication Cables (800-52 (d)), MI (article 332). Fire Alarm Systems (article 760), Emergency Systems (article 700), Optical Fiber Cables (article 770) and Intrinsic Safety (section 504-30). The requirements in these sections are complex. We will discuss them in detail and the general noise problem in the next CableGram.

The requirements for cables that have an outer metal armor are less than for plastic jacketed cables. The general rule is separate communication, control, signal, and instrumentation cabling from power cabling. Power cabling includes 460-volt motor power, 120-volt power, and lightening circuits. Note 120-volt circuits can generate noise. Generally, a separation of two inches is minimum, but the individual circuit and cable are the determining factors in separate requirements.

Question: What types of cables can be installed in Cable Tray systems?

Answer: The types of cables permitted by the 2005 NEC are indicated in Section 392.3 uses permitted, (a) Wiring Methods. They include:

  • Power and Control Tray Cable (Type TC) – NEC Article 336
  • Power Limited Tray Cable (Type PLTC) – NEC Sections 725-61?and 725.82(E) Instrument Tray Cable (Type ITC) – NEC Article 727
  • Optical Fiber Cables – Article 770
  • Fire Alarm Circuit Conductors – Article 760
  • Communication Cables – Article 800
  • Mineral Insulated (MI)Cable – Article 332
  • Metal Clad (MC) Cable – Article 330

and other cables, including those specially approved for installation in cable trays. Medium voltage (type MV) and single conductor cables in sizes 1/0 and larger are permitted with some restrictions in Industrial Establishments where qualified persons service the installation.

 

Source: Cable Tray Institute (CTI)

Where? Job site and installation considerations

1.Outdoor

> supports available affect the length and strength requirements

> environmental loads, ice, wind, snow, and possibly seismic

> corrosion requirements affect the materials and finishes

> classified hazardous locations affect the cable types acceptabl

2 . Indoor

> support locations available affect the length and strength of the system

> industrial installation may require a 200 lb. Concentrated Load

> commercial or institutional installation may make system appearance, system weight, and space available important factors

> environmental air handling area may affect cable types, cable tray material, or cable tray type and need for covers

> classified hazardous locations affect the cable types acceptable

 What?

1.Type and number of cables to support

> NEC cable fill requirements dictate size, width and depth, of system

> cable support requirement may control bottom type

> largest bending radius of cable controls fitting radius

> total of cable weight determines load to support

 

2.Future requirements

> cable entry / exit freedom

> design partially full or an expandable system

> support type to allow for needs

Source: Cable Tray Institute (CTI)

  • Trapeze Support (Single or Multi-tier)
  • Hanger rod clamps, “J” hangers
  • Center Hung Support
  • Wall Support
  • Underfloor Support
  • Pipe stanchions or other structures

Each of these support methods are preferable in different applications. For instance, trapeze supports may be desired in an application where cables will be pulled through the cable tray. Center hung supports, on the other hand, are generally used when cables will be installed from the side of the cable tray. Center hung supports are especially useful when future cable additions are desired. Wall supports and underfloor supports are useful when ceiling structure is not available or undesired. Outdoor installations are controlled by the structures available to support the cable tray.

Source: Cable Tray Institute (CTI)

  • Straight sections are available to route cables in a horizontal or vertical plane.
  • Fittings are available to route cables in various
    directions in either the horizontal or vertical planes. Typical
    examples of fittings include elbows, tees, crosses, and risers. Each of
    these fittings are available in various radii and bend angles.
  • Covers are accessories and shouldn’t be in here unless splices etc. are included.

Source: Cable Tray Institute (CTI)

1. Steel (Min. Yield = 33KSI) (35 KSI for Stainless)

  • Plain: hot rolled pickled and oiled steel per ASTM A569 (Commercial Quality) or A570 (Structural Quality)
  • Pre-Galvanized: mill galvanized steel per ASTM A653 CS (Commercial) or SS (Structural) G90
  • Hot Dip Galvanized After Fabrication: plain steel which is hot dipped after fabrication per ASTM A123.
  • Stainless Steel: type 304 or 316L fully annealed stainless steel

 

2. Aluminum (Min.Yield = 23 KSI)

  • 6063-T6 or 5052-H32 alloy per ASTM B209

 

3. Fiber Reinforced Plastic (FRP)

  • Polyester and Vinyl Ester resin systems available
  • meet ASTM E-84 smoke density rating; Polyester 680, Vinyl Ester 1025
  • Class 1 Flame Rating and self-extinguishing requirements of ASTM D-635.

Source: Cable Tray Institute (CTI)

Cable tray are available 6 types:

  • Ladder
  • Solid Bottom
  • Trough
  • Channel
  • Wire Mesh
  • Single Rail

 

Source: Cable Tray Institute (CTI)

The National Electrical Code publishes the standards for all types of electrical applications. Articles 318, 250, and 800 cover various aspects of cable tray systems.

NEMA, (National Electrical Manufacturers Association), is an association comprised of the major cable tray manufacturers in the industry. This committee has published three documents to date: NEMA VE1, FG1 and VE2.

NEMA VE1 covers general cable tray definitions, manufacturing standards, performance standards, test standards, and application information. Free download of this document is available on the NEMA website.

NEMA FG1 addresses the standards for fiberglass cable tray systems. Free download of this document is available on the NEMA website.

NEMA VE2 is a cable tray installation guideline which covers receiving and unloading material, storage of material, and general installation practices. Free download of this document is available on the NEMA website.

CTI, (Cable Tray Institute), is a trade association comprised of the major cable tray manufacturers in the industry and was formed to provide specifiers, designers, and installers information on the advantages of using cable tray systems over other types of products. (i.e. conduit, ladder rack, etc.)

Source: Cable Tray Institute (CTI)

Per the National Electrical Code, a cable 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.”

What does this mean?

  • Cable trays support cable the way that roadway bridges support traffic.
  • A bridge is a structure that provides safe passage for traffic across open spans.
  • Cable tray is the bridge that allows for safe transport of wires across open spans.
  • Therefore, think of cable tray as the structural component of a building’s electrical system

 

Source: Cable Tray Institute (CTI)