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This article discusses how the requirements in both the installation code and the product standard are utilized to manufacture and install power and control tray cable, Type TC, products that are suitable for various applications. Where appropriate, alternate wiring methods are identified to provide some useful comparison. Also, some of the applicable requirements in Canada and Mexico1 are identified and discussed to provide a North American perspective.

Installation and Applications Requirements
Table 1 [pdf]  provides a brief comparison of installation and applications requirements for Type TC tray cables in Canada and the US. Significant requirements for product recognition and application are identified. Since Type TC cables are typically used in cable trays, references related to cable trays are also identified. For complete details, references provided in the table should be consulted.

In the US, the National Electrical Code (NEC), NFPA 70 standard, recognizes various types of wire and cable products and also defines requirements for their uses and installations for intended applications. Most, if not all, of these products are manufactured and listed in accordance with applicable product standards, generally developed by the Underwriters Laboratories (UL). Article 318 defines cable trays, in 318-2. Cable tray installations are used more commonly in industrial establishments to provide flexibility in wiring of process equipment. In accordance with 318-3, cable tray installations are not limited to industrial establishments. However, single conductor cables, provided they are identified for use in cable trays, are limited to industrial establishments only in accordance with 318-3(b)(1).

Article 340 of the NEC recognizes Type TC products and defines requirements for their uses and installations in cable trays, in raceways, or where supported by a messenger wire. UL Standard 1277, Electrical Power and Control Tray Cables with Optional Optical-Fiber Members, defines prescriptive and performance requirements for Type TC products. For their use in cable trays, the suitability of single conductor cables, which are recognized in Table 310-13, is evaluated in accordance with their respective product standards.

In Canada, the Canadian Electrical Code (CEC) Part I, CSA Standard C22.1, recognizes various types of wire and cable products and also defines requirements for their uses and installations for intended applications. All of these products are manufactured and listed in accordance with applicable product standards listed in Appendix A of the CEC Part II.2 These standards are developed by the Canadian Standards Association (CSA). In Canada, a cable tray is considered a "raceway." Unlike US, Type TC tray cables can be either single or multi-conductor product in accordance with CEC. Also, tray cable in Canada also includes medium voltage power cables. Type TC tray cables shall be permitted in cable trays only in areas of industrial establishments that are inaccessible to the public, as an alternate to the main rule which requires that the conductors used in cable trays in all areas shall have a continuous metal sheath or interlocking armor. Similar to US, single conductor Type TC tray cables shall not be smaller than 1/0 AWG.

Cable trays provide the needed flexibility in circuit layouts in various industrial establishments, such as those found in petro-chemical, pulp and paper, textile, mining, etc. Wire and cable products used in various non-raceway applications in these industries require superior mechanical, flame test, and cold temperature handling properties.

Armored cables, such as Type MC Cables in US and Types AC90, ACWU90 and TECK90 in Canada, have been the primary choice for these applications. This is because these products can be installed by themselves or in cable trays. Type TC cables require a protection when outside of the cable trays while armored cables may not require such protection in most cases.

Inherent construction design of armored cables provides a better opportunity to attain higher levels of mechanical perfor-mance, flame test performance for the overall cable construction, a higher level of insulating properties for the conductor insulation, and a higher level of cold temperature properties for the cable. Similar level of achievement is difficult with Type TC products, especially when the jacket alone cannot provide the needed performance for all different needs.

Additional applications, such as for control and signal circuits, of Type TC cables are identified in Table 1. The installation requirements for various wire and cable products in cable trays are provided in the code references for cable trays in Table 1. In particular, these references should be consulted for clearances between the cable trays, spacing of conductors and cables within a cable tray, securing of conductors and cables within a cable tray, etc. These installation requirements for cable trays determine permitted ampacity for conductors and cables installed in a given cable tray.

Mechanical loading of trays is also a critical factor for proper installation of cable trays. In general, Type TC tray cables provide an advantage over heavier armored cables. Generally, the weight of these products would decrease in the following order: armored cables with copper conductors, tray cables with copper conductors, armored cables with electrically equivalent size aluminum conductors, and tray cables with electrically equivalent size aluminum conductors.

Photo 1. Ladder-type tray supporting conduit at transition.

Photo 2. Transition from EMT to cable tray--communication circuits.

Photo 3 and Photo 4. Ladder-type cable tray and conduit supports at transition points.

Photo 5. Ladder-type cable tray with external equipment grounding conductor connected

Construction and Performance Requirements
Table 1 also provides a comparison of the construction and performance requirements for Type TC tray cables in two countries. With few exceptions, the requirements are very similar. Typical constructions of Type TC with three and four conductors with an equipment grounding conductor for power applications are shown in Figures 1 and 2.

Insulated conductors recognized in Table 310-13 of the NEC are cabled together with or without the equipment grounding conductor and fillers. Conductor types used most commonly for 600 V rated Type TC products include THHN/THWN, XHHW, and RHH/RHW. For 2000 V rated Type TC products, conductor types used include RHH/RHW recognized in Table 310-62 of the NEC. A separator tape is used to wrap the assembly of conductors. An overall jacket is then applied over the assembly.

Materials for conductor insulation, fillers, tapes, and jacketing play an important role in delivering the required performance in accordance with the listing requirements, optional requirements, customer specifications and industry practices for Type TC products. A balance between the electrical, mechanical and flame test properties of the insulation type; mechanical and flame test properties of the overall construction; and required optional performance capabilities is arrived at by the users in various industrial establishments for their specific needs. Construction capable of meeting the requirements for a higher level of low temperature handling, a higher level of vertical flame test, for a lower level of acid gases, etc., is different than the construction capable of meeting the normal requirements for the same properties.

Summary
Examination of code and standards requirement in North America suggests that the interactive system of Code-Product Standards-Verification provide a set of choices for wiring methods in demanding environments in the industrial establishments. Power and Control Tray Cable – Type TC products can be used successfully in many applications in these environments. It is also clear that there is no single construction of Type TC that is suitable for all possible applications. Selection of a specific design depends upon the installation conditions and the required product performance characteristics for a particular application. Also, versatility, availability, and costs of alternate wiring methods, such armored cables and conductors in raceways, are compared against the similar features of Type TC cables and associated cable tray installation.

1 The installation code (NOM-001-SEMP-1994) recognizes Type TC products in Article 340. However, it is being revised and at present time there is no known product standard in place for Type TC products in Mexico, limited information from Mexico is presented here. Since the installation code in Mexico is likely to remain similar to the NEC, it also likely that the product standard, when developed, for Type TC products will be similar to UL 1277.

2 In Canada, Appendix A in CEC Part II is an integral part of the Code.

Ravindra H. Ganatra is a senior engineer for distributor products at Alcan Cable’s head office in Atlanta, Georgia. Ravi has been involved in several areas of wire and cable manufacturing, including: product, process and materials development; product applications; and codes and standards development activities in ASTM, CANENA, NEMA, NFPA, and UL. He is a principal member of CMP-6 and an alternate member of CMP-7 of the NEC.

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