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Home / Technical Articles / Practices for grounding and bonding of cable trays

Metallic Cable Trays

Cable tray may be used as the Equipment Grounding Conductor (EGC) in any installation where qualified persons will service the installed cable tray system. There is no restriction as to where the cable tray system is installed.

Practices for grounding and bonding of cable trays
Practices for grounding and bonding of cable trays (photo credit: whereis.com)

The metal in cable trays may be used as the EGC as per the limitations of table 392.60(A). All metallic cable trays shall be grounded as required in Article 250.96 regardless of whether or not the cable tray is being used as an equipment grounding conductor (EGC).

The EGC is the most important conductor in an electrical system as its function is electrical safety.

Grounding and bonding of cable trays
Grounding and bonding of cable trays

There are three wiring options for providing an EGC in a cable tray wiring system:

  1. An EGC conductor in or on the cable tray.
  2. Each multi-conductor cable with its individual EGC conductor.
  3. The cable tray itself is used as the EGC in qualifying facilities.

Correct bonding practices

To assure that the cable tray system is properly grounded

If an EGC cable is installed in or on a cable tray, it should be bonded to each or alternate cable tray sections via grounding clamps (this is not required by the NEC® but it is a desirable practice)

In addition to providing an electrical connection between the cable tray sections and the EGC, the grounding clamp mechanically anchors the EGC to the cable tray so that under fault current conditions the magnetic forces do not throw the EGC out of the cable tray.

A bare copper equipment grounding conductor should not be placed in an aluminum cable tray due to the potential for electrolytic corrosion of the aluminum cable tray in a moist environment.

For such installations, it is best to use an insulated conductor and to remove the insulation where bonding connections are made to the cable tray, raceways, equipment enclosures, etc. with tin or zinc plated connectors.

NEC Table 250.122 – Minimum size equipment grounding conductors for grounding raceway and equipment

Minimum size equipment grounding conductors for grounding raceway and equipment
Table 2 – Minimum size equipment grounding conductors for grounding raceway and equipment

Aluminum Cable Tray Systems

Table 392.60(A) – Metal area requirements for cable trays used as equipment grounding conductors

Metal area requirements for cable trays
Metal area requirements for cable trays used as equipment grounding conductors

For Sl units: 1 square inch = 645
* Total cross-sectional area of both side rails for ladder or trough cable trays or the minimum cross-sectional area of metal in channel cable trays or cable trays of one-piece construction.
** Steel cable trays shall not be used as equipment grounding conductors for circuits with ground-fault protection above 600 amperes. Aluminum cable trays shall not be used as equipment grounding conductors for circuits with ground-fault protection above 2000 amperes.


Table 392.60(A) “Metal Area Requirements for Cable Trays used as Equipment Grounding Conductors” shows the minimum cross-sectional area of cable tray side rails (total of both side rails) required for the cable tray to be used as the Equipment Grounding Conductor (EGC) for a specific Fuse Rating, Circuit Breaker Ampere Trip Rating or Circuit Breaker Ground Fault Protective Relay Trip Setting.

These are the actual trip settings for the circuit breakers and not the maximum permissible trip settings which in many cases are the same as the circuit breaker frame size.

If the maximum ampere rating of the cable tray is not sufficient for the protective device to be used, the cable tray cannot be used as the EGC and a separate EGC must be included within each cable assembly or a separate EGC has to be installed in or attached to the cable tray.

For specific areas requiring bonding for electrical continuity, refer to Figures 1-4.

Expansion splice plates and horizontal adjustable plates
Figure 1 left: Expansion splice plates; Figure 2 right: Horizontal adjustable plates

Figure 3 left: Discontinuos segments; Figure 4 right: Cable tray sections vertical adjustable splice plate
Figure 3 left: Discontinuos segments; Figure 4 right: Cable tray sections vertical adjustable splice plate

Non-metallic cable trays do not serve as a conductor. It is also recommended that wire mesh cable trays not be used as an equipment grounding conductor.

Although permitted by the NEC, it is recommended due to the unique nature of the wire mesh, fittings are manufactured in the field from straight sections by cutting away the current carrying structural wires, reducing the current-carrying capability of the system. As such, the use of wire mesh cable trays as an equipment grounding conductor is not recommended.

If the wire mesh cable tray is to be used as an equipment grounding conductor, then the installation of a ground wire is recommended.

If a wire mesh cable tray is supporting cable with a built-in equipment grounding conductor or control or signal cables, then the tray should have a low impedance path to a non-system ground to reduce noise and remove induced or stray currents. A separate grounding cable attached to the wire mesh cable tray is not usually required.


References:
  • CABLE TRAY MANUAL Based on the 2011 National Electrical Code – EATON
  • Cable Tray Installation Guidelines – NEMA Standards Publication VE 2-2006

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.

14 Comments


  1. Joali
    Apr 19, 2023

    I have a question: this article states that it is best to use insulated cable, and to remove the insulation where bonding connections are made to the cable tray. What is the justification of using insulated cable? why not a bare copper grounding cable.?


  2. Carlos Juarez
    Mar 02, 2023

    can you put two bond jumpers on the same nut and bolt on cable trays or do we use separate nut and bolt for the second jumper.


  3. JD Anderson
    Mar 25, 2021

    Contractor installing TC Cables size #14’s in tray, the multi conductor their installing doesn’t have a green identifier. The contractor pulled a green single conductor #14 along with the multi-conductor cable. Does the NEC Code allow this application? The reason is – on TC Cable, having green as one of the conductors has to be special ordered, not a shelf item.


  4. Vanthong Phothichak
    Mar 30, 2019

    Dear Sir/Madame,

    please advise me, now i install cables (multi-core power cables) on cable tray, can i install cables on to each other? due to the cable tray is limited of space.

    Nui.


  5. Paul Abernathy
    Mar 10, 2019

    Greetings Edvard,

    Less we not also forget the beneficial provisions of 250.122(F)(2) as well when the installer of traditional multiconductor cable assemblies are used, such as MC Cable or TC Cable to name a few. Traditionally the EGC in these cables are designed via their associated UL/ANSI Standard for use based on the OCPD protecting the single cable assembly so they aren’t intended for parallel use. However, where used as such the benefits of using 250.122(F)(2) just may save the day. So if you are using standard cable assemblies in a cable tray, in parallel, be sure to check out 250.122(F)(2) as it just may keep you from having to buy specially made cables.


  6. Ilyas Ahmed
    Jan 09, 2018

    How we have to select the earth bonding cable for instrument cable trays and electrical cable trays. i’m asking this because i’m working on site i don’t know which size of conductor i have select for instrument cable tray as well as electrical cable tray we have 15 to 20 instrument cables in instrument cable tray and 5(five)3c*240sqmm cables in electrical cable tray so which size will be suitable for both E & I trays..kindly explain me in detail so that it will be easy for everyone to select the cable for bonding as well as earthing


  7. Brendan Gonzalez
    Aug 26, 2016

    I have a question and can not seem to find it written anywhere. I am looking for an answer to verify that when grounding tray to earth on one cable tray run is the correct way and not having multiple tray to earth grounding which confuses the path in my opinion. I have an individual going against some engineered drawings and secretly having electricians add multiple tray to earth grounds on one cable tray run that’s 80 foot long. I’m looking for a NEC code stating anything about this so I can bring this up with written documents. Thanks


    • Richard Buck
      Jan 22, 2021

      If you only use one bonding/ground point at one end of the tray or the other…you have the whole section unprotected and with resistance increasing with length…that one ground may not be enough. When installing tray for Comm, we (as per TIA/BICSI standard) would attach to bldg steel at beginning, the end and every 50ft. Most comm tray is not used as an EGC so I would think that would be the direction you would take…is your tray an EGC…if so…follow the NEC


  8. Bertrand BOUTIN
    Jun 01, 2015

    Mecatraction devloped a patented solution,
    innovating and no tool way of instaling earthing on cable trays, permitting to reduce time instalation by at least 5 time.

    My contact is visible on Mecatraction website, US market, please feal free to contact me if interested.

    Regards.


  9. Nikhil Garde
    May 22, 2015

    Thanks for the giving important thing – Earthing which is very important in Electrical Installations


  10. komichi
    Mar 09, 2014

    man,y thanks our teacher


  11. Peter Olufemi
    Mar 03, 2014

    Thank u so much. You have thought me more than i knew in electrical engineering.Thank u once again.


  12. Eng. Ruqi
    Feb 27, 2014

    Thanks a lot EEP.


  13. muqtar
    Feb 27, 2014

    Thanks,

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