05-April-2022 || By: Admin
A cable tray system's purpose as part of a cable management system is to support, route, and protect cable. Hutaib Electricals gives guidance on the proper use and installation of cable tray systems according to NEMA .
The cable tray system is just one part of the overall cable management system. The cable is, of course, an important component. As a result, it is also critical to understand how to apply and install cables in a cable tray system. To that end, this Bulletin will go over the most common cable types used in cable trays, as well as the wiring methods permitted in cable trays under the National Electric Code.
Tray rated cables, in general, are high-quality products that have been rigorously tested to withstand the rigors of harsh environments. They are shielded by a plastic jacket or metal armor that is placed over individual conductor insulations. They can be rated for outdoor, indoor, corrosive, hazardous, or high electrical noise environments. They should be UL listed, indicating that they have been tested for flammability resistance, mechanical resistance, and temperature limits. Many cable tray rated cables are exposed rated and include a crush and impact test as part of the listing (ER). ER cable can leave the cable tray for up to six feet as long as it is supported and secured.
In many cases, there is more than one type of cable for a given application; for example, for 600-volt motor power cables, both tray cable (TC) and metal clad (MC) cables can be used. Cables used in a cable tray system should always be UL listed and labeled as cable tray rated.
The most frequently used tray cables are:
1) Instrumentation Tray Cable-: Instrumentation cables are available in shielded or unshielded constructions with multiple single conductors, unshielded or shielded twisted pairs, and with or without metal armor. They have a 300 volt insulation rating and come in sizes ranging from 22 AWG to 12 AWG. PLTC(Power Limited Tray Cable) cables are designed for Class 3 and Class 2 non-plenum and non-riser circuits. They are intended for use with power limiting circuits.
ITC cables can be installed in industrial settings where the maintenance and supervision conditions ensure that only qualified personnel service the installation. They can be installed in cable trays, raceways, hazardous locations, as an aerial cable on a messenger, direct burial where indicated for use, under raised floors in rooms containing industrial equipment, and under raised floors in rooms containing information technology equipment.
ITC cables may not be installed with power, lighting, non-power limited Class 1 circuits, or non-power limited circuits unless they have a metallic sheath and are terminated within equipment or junction boxes, or separations are maintained by insulating barriers.
2) Metal Clad Cables-:Instrumentation cables are available in shielded or unshielded constructions with multiple single conductors, unshielded or shielded twisted pairs, and with or without metal armor. They have a 300 volt insulation rating and come in sizes ranging from 22 AWG to 12 AWG. PLTC(Power Limited Tray Cable) cables are designed for Class 3 and Class 2 non-plenum and non-riser circuits. They are intended for use with power limiting circuits.
Type MC cables are widely used in 600 volt and MV power distribution, lighting, and control applications. In accordance with Articles 330 and 725 of the NEC, they are permitted for use on services, feeders, and branch circuits for power, lighting, control, and signaling circuits. Type MC cables can be installed indoors or outdoors, wet or dry, in wet or dry locations, in hazardous locations (Class I, Division I), in cable tray, as aerial cable on a messenger, in any approved raceway, direct burial (where identified), or encased in concrete (where identified). MC cables are not permitted to be installed in locations prone to physical damage. MC cables must be supported and secured at six-foot intervals.
3) Cables for Fire Alarms-: Fire alarm circuits and cables are divided into two types: power limited and non-power limited. Cables for either type of circuit may be further classified as (CI), indicating that they have met the requirements to ensure the continued operation of critical circuits under fire conditions for a specified time. Power-Limited-Fire Alarm (PLFA) circuits are fire alarm circuits that are powered by a 760.121-compliant source (listed PLFA or Class 3 transformer, Listed PLFA or Class 3 power supply, listed equipment marked to identify the PLFA power source.)
PLFA fire alarm cables, like communication and optical fiber cables, are further marked relative to their fire propagation potential, indicating the permitted areas of use. There is also a hierarchy for allowed cable substitution in power-limited circuits, which includes communication cables.
4) Cables for communication-:Communication cables, like optical fiber, are used to transmit data signals. Coaxial conductors, copper conductors, or twisted wire pairs can be used to accomplish this. These cables are used in a wide range of applications, including recording studios, data transmission, radio transmitters, intercoms, electronic circuits, and RF shielding. Communication cables are defined by the NEC as a factory assembly of two or more conductors with an overall covering. One or more metallic members, strength members, or jackets may be used to cover the conductor assembly. Ethernet cables are a popular type of communication cable that is frequently listed and installed in accordance with NEC.
5) Optical Fiber-: The medium and technology associated with the transmission of information as light impulses along a glass or plastic wire or fiber are referred to as fiber optic (or "optical fiber"). Fiber optic wire carries far more information than copper wire and is far less susceptible to electromagnetic interference.
An optical fiber cable is a cable that contains one or more light-carrying optical fibers. Individual optical fiber elements are typically coated with plastic layers and housed in a protective tube appropriate for the environment where the cable will be deployed. Different types of cable are used for various applications, such as long-distance transmission or high-speed data transmission between different parts of a building.
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