Metallic cable tray continues to gain popularity in the United States as an alternative to conduit for routing, supporting and managing wire and cable in all facility types.   Metallic cable trays address the exponential increase of cable runs and provide cost effective expansion solutions. Two designs illustrate the variety of products available: ladder tray is best for heavy wires and wire mesh cable tray is well suited for voice/data/video installations. Product selection, installation practices and code compliance improve when familiar with applicable standards and information resources.    

Two major organizations are responsible for prevailing standards: the National Electrical Manufacturers Association (NEMA) for standards on the manufacturing of the tray, and the National Fire Protection Association (NFPA) for standards on the installation of the tray.

Underwriters Laboratories (UL), an international independent not-for-profit safety testing and certification organization, to which companies submit products, also plays an essential role.  

Cable tray manufacturers who are members of NEMA conform to the applicable NEMA standard, VE-1, which covers the manufacturing parameters of metallic cable tray and how cables are supported by it. By voluntarily adhering to the standard, which is a guideline but not a law, a manufacturer self declares that its products conform to nationally recognized design specifications and are safe to use. NEMA also publishes standard VE-2, the manufacturers’ recommended installation practices.

The prevailing standard for safe installation of metallic cable tray is Article 392 of the National Electrical Code Ò (NEC), which is by the NFPA and primarily deals with safe practices for electrical installations. Municipalities may choose to adopt the code. If they do, the NEC requirements become part of the local law and products and any installation covered by the requirements are then subject to approval by municipal electrical inspectors having jurisdiction.

This is where UL comes into play. To reduce the likelihood of electrical shock and fire hazards, Section 392.7(A) of the NEC requires metallic cable tray and all fittings maintain continuous grounding. Section 392.7(B) permits steel or aluminum cable tray systems to be used as equipment grounding conductors if they meet the four requirements detailed in that section.

To assist the inspector and the installer in verifying the metallic cable tray system complies with the requirements detailed in Section 392.7(B), manufacturers use independent testing and certification services provided by UL. The various components used to complete the equipment grounding path in the cable tray installation - tray, bolt, splice, fastener, connector, bonding jumper, etc. – must be evaluated if the manufacturer desires to label the product with the UL Mark.  

“Evaluation of the cable tray involves examination of the cable tray system to determine its suitability as an equipment grounding conductor,” notes Robert Osborne, Principal Engineer (PDE) – for Power Distribution Equipment, Underwriters Laboratories Inc. “The UL Mark provides assurance that the cross sectional area marked on the product is accurate. UL also performs an electrical resistance test on the joints of the cable tray system. This resistance test is conducted on the system configured with the minimum mechanical securement provided by the manufacturer. In some system, mechanical securement is accomplished without separate hardware (e.g., bolts). In these cases, Section 392.7(B)(4) requires that the installer complete the installation with appropriate hardware or bonding jumpers as required by Section 250.96 or 250.102.”

Upon successful completion of testing, UL issues a report that certifies compliance of the products tested and permits the use of a specific UL Mark on the products. It is in the best interests of manufacturers to obtain UL Listing for their products as the UL Mark is a useful tool in assuring the suitability of the installation with respect to grounding of electrical equipment. In the case of cable trays, the UL mark is a useful tool for the inspector and the installer.

Electrical products may bear the UL Mark indicating either UL “Listed” or UL “Classified.” The words Listed and Classified are part of the UL identification system – each a particular type of certification service that UL provides.  

“Listed” means representative samples of a product met UL’s safety requirements, which are primarily based on UL’s published Standards for Safety. “Classified” means representative samples of a product have been evaluated but only with respect to specific properties, a limited range of hazards, or suitability for use under limited or special conditions. UL allows the   “Classified” Mark to be applied to cable trays that have been successfully evaluated to NEC 392.7, for continuous grounding. The evaluation covers only one aspect – continuous grounding. It does not include testing for load capacity, impact resistance, shock, vibration, and other possible factors that could be a consideration.

Cable tray that is authorized to use the UL Classification Mark must have the mark on the product that consists of UL’s Classification Logo, including UL’s symbol (a circle enclosing the capital letters UL, with the U to the left and slightly higher than the L), the word “Classified”, and the following statement – “CLASSIFIED BY UNDERWRITERS LABORATORIES INC. Ò AS TO ITS SUITABILITY AS AN EQUIPMENT GROUNDING CONDUCTOR ONLY.” Directly beneath this statement is the UL-assigned control number, which is a unique number assigned by UL to identify the manufacturer of the Classified product.

When UL is of the opinion that a UL Classified product is too small or irregularly shaped or textured to accept the complete and legible Classification marking directly on the product (such as with wire cable tray), the Classification Mark can then, at UL’s discretion, appear on the smallest unit container in which the item is packaged.  

Project designers and engineers often specify UL Classified and UL Listed products as a way of helping ensure that a project meets local code. Often, the specification may state, in clear terms, that the product must bear the UL Mark. Alternately, the specification may state that the product being specified for a particular use must meet the requirements of UL Inc. for that product and that the UL Mark on the product is acceptable as evidence of compliance.

Bio: Steven Groner is the Director Of Marketing at GS Metals Corp. GS Metals manufactures a range of cable trays. Flextray® Cable Management Systems are leaders in the wire mesh market. Globetray® Ladder Trays and Globe Strut® Channel Framing have been installed worldwide for over 50 years. Hardware, fasteners, hangers and engineering assistance for all systems complete the GS Metals package. All products are available through a national distribution network. www.gsmetals.com, 800-851-9341