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 email@example.com. Check out his Tech Shack blog.
Tech Talk Tool Tip
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