The following are some of the changes in Article 318, Cable Trays, that we can expect in the 1999 NEC. These changes are based on the actions taken at the May NFPA meeting. The new 1999 National Electrical Code will be available from the NFPA in September. To obtain a copy contact: The National Fire Protection Association, 1 Battery March Park, P.O. Box 9101, Quincy, MA 02269-9101; Tel. No.: 1-800-344-355. Please compare this Cablegram with final 1999 NEC. There are a considerable number of changes in the new code which we will discuss in this and subsequent Cablegrams.

The National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association.


Note: The CTI is a strong participant in the code process. We submitted 14 code proposals and 8 public comments during this code cycle.

1 – Section 318-1 – Scope

This section will be changed to:

318-1 Scope. This article covers … ladder, ventilated trough, ventilated channel, and solid bottom, etc.

The word ventilated has been added before ‘trough’ and ‘channel’ to provide consistent wording with other parts of Article 318.

2 – Section 318-2 – Definition

This section will be changed to:

318-2 Definition. Cable Tray System: A unit … forming a structural system used to securely fasten or support cables and raceways.

The CTI proposed to replace the words ‘rigid structural’ with ‘mechanical.’ The final code panel action was to use the word ‘structural,’ delete ‘rigid,’ and add the words ‘securely fasten or.’ The panel’s statement indicated that its intent is not to require cables or raceways to be securely fastened but rather to allow cables or raceways to be securely fastened.

3 – Section 318-2 – Definition

There was a proposal to require a cable tray system to be listed but the code panel rejected it. The panel statement on this action included:

  • Cable trays are a support system
  • Installations are application specific
  • Instructions from the manufacturers will properly cover the issues

4 – Section 318-3 Uses Permitted

Fire Alarm Cables (Article 760) and multipurpose and communication cables (Article 800) were added as acceptable wiring methods. See NEC Sections 760-28 (c) and 800-52 (d) of the 1996 code.

5 – Section 318-5 Construction Specifications
(c) Corrosion Protection

This section will change the word “metal” to ferrous material, delete the word “adequately”, and add a reference to 300-6.

(c) Corrosion Protection: Cable tray systems shall be corrosion resistant. If made of ferrous material, the system shall be protected from corrosion as required by Section 300-6.

Note: It is not clear which parts of 300-6 apply to cable trays. We will cover corrosion protection and 300-6 in a future Cablegram.

6 – Section 318-6 Installation

(a)Complete System

This section will be changed to:

(a) Complete System:

There was no change in the first paragraph except the last sentence on bonding was moved to a new third paragraph and reworded.

A new second paragraph was added to require a maximum of six feet support distance between cable trays and cable trays and equipment for single conductor cables.

The second paragraph is a new requirement for a support distance for single conductor cables which is not covered in the present code.

Note: The new code says individual conductors but the term single conductors could also be used.

7 – Section 318-11 – Ampacity of Cables Rates 2,000 Volts or Less in Cable Trays

(b) Single Conductors —Note: Sectional thru 3 had editorial changes.

(4) Where single conductors … (2.15 x OD) of largest conduction contained within the configuration and adjacent conduction configurations of cables. No change in the rest of this paragraph.

The substantiation for this change is:

The present wording requires “a maintained space of not less than 2.15 times one conductor diameter (2.15 X O.D.) between circuits.” There is no reference to other conductors or cables, such as single conductors or multi conductor cables. The use of the word “circuits” provides no guidance for installations involving other conductors or cables which do not comprise a circuit. For instance, the present code would allow single conductors to be adjacent to the conductors configured in a triangle or square.

The proposed wording also provides clear direction on how to measure the required space.