Tech Talk: Cable Trays Keep Projects Tidy
A Half-Dozen Mysteries Answered
Now let’s take a moment to consider some commonly asked questions – a few of which are lifted from CTI materials – surrounding the use of cable trays.
Can a metal cable tray be classified as a cabling “raceway”?
No. Even though the National Electrical Code (NEC) defines a raceway as an enclosed channel of metal expressly designed for holding wires, this exception is made because a cable tray is an “open” structural system.
Can mechanical utility piping or tubing containing compressed air be installed in a cable tray with cabling?
No, NEC section 300.8 does not permit this; only electrical cabling.
I recently noticed that a cable tray was used for some low-voltage cabling and there was no indication of the tray being grounded. Is this a NEC violation?
Actually, low energy systems may not be required to be grounded for shock and arcing. However, it is a good idea to shield for noise, electromagnetic interference (EMI) and lightning protection. A good free reference for cable tray installations can be found in the National Electrical Manufacturers Association (NEMA) VE-2 document (www.nema.org/stds/ve2.cfm).
Do you need to provide cable ties with cabling in a cable tray?
Yes, you need to tie them down to maintain spacing and separate cable-type groups. You will see some indications of not having to tie down in horizontal cable trays, but in other cable type groups it may be necessary. It is a good practice to keep all cabling secured in the tray and properly separated.
Are cable trays UL-Listed?
Metal cable trays are not required to be listed because they are support systems. However, there are UL-Listed trays and you should be careful to comply with what your AHJ requires. Remember the cautions elsewhere in this article on modifying UL-Listed cable trays.
Can a person walk on an installed cable tray system?
No, walking on cable trays is not permitted.
Bob Dolph has served in various technical management and advisory positions in the security industry for 30+ years. To share tips and installation questions, E-mail Bob at bdolph.ssi@gmail.com. Check out his Tech Shack blog.
Tech Talk Tool Tip
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About the Author
Bob Dolph, SSI Contributor
Bob is currently a Security Sales & Integration "Tech Talk" columnist and a contributing technical writer. Bob installed his first DIY home intercom system at the age of 13, and formally started his technology career as a Navy communication electronics technician during the Vietnam War. He then attended the Milwaukee School of Engineering and went on to complete a Security Management program at Milwaukee Area Technical College. Since 1976, Bob has served in a variety of technical, training and project management positions with organizations such ADT, Rollins, National Guardian, Lockheed Martin, American Alarm Supply, Sonitrol and Ingersoll Rand. Early in his career, Bob started and operated his own alarm dealership. He has also served as treasurer of the Wisconsin Burglar and Fire Alarm Association and on Security Industry Association (SIA) standards committees. Bob also provides media and training consulting to the security industry.
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