Types of Electric Power Cables
Introduction to Electric Cables (Detailed Definition):
An Electric Power Cables are factory assembly of two or more conductors having an overall covering. Several types of cables are manufactured for specific applications. A cable has one or more insulated conductors usually covered with a protective jacket. Cable types used in commercial and industrial wiring applications include armored, metal-clad, nonmetallic-sheathed, mineral-insulated, tray cable, service-entrance, underground feeder and branch-circuit, low-voltage, and medium-voltage.
A tray cable (TC) is a cable that consists of two or more insulated conductors enclosed in a flame-retardant, nonmetallic jacket and is used for installation in cable trays or raceways. See Figure 1.
Underground Feeder and Branch- Circuit Cables
An underground feeder and branch-circuit (UF) cable is a cable that has a moisture- resistant jacket and is listed for direct burial in the earth. Type UF cable is constructed with THWN conductor insulation and bound in a PVC outer jacket, which makes it suitable for wet locations such as direct burial. Type UF cable can also be installed in cable trays. See Figure 2:
Type UF cable is typically used with outdoor loads such as pumps and lighting. Type UF cable can also be used for the same applications as NM cable. Type UF cable is resistant to moisture, fungus, and corrosive materials, and can replace NMC cable in damp locations.
A service-entrance (SE, USE) cable is a multi-conductor cable with or without an overall covering. See Figure 3.
A low-voltage cable is a cable that can be single-conductor or multi-conductor and is rated from 0 V to 600 V. Low-voltage cables are used in industrial and commercial applications for power, lighting, control, signal, and communication circuits. Low-voltage cables can be installed indoors, outdoors, in cable trays, in raceways, direct buried, or as part of a messenger system (in outdoor locations).
Low-voltage cables are composed of bare stranded copper conductors, conductor insulation, and a moisture-resistant PVC jacket. Low-voltage cable can be types TC, MC, SE, or USE. See Figure 4.
A medium-voltage (MV) cable is a cable that can be single-conductor or multi- conductor and is rated from 2001 V to 35,000 V. Because of higher operating voltages, MV cables are typically constructed differently than low-voltage cables. See Figure 5.
Type MV cables have a solid dielectric insulation and a conductor shield surrounding the conductor. A conductor shield is a non- magnetic material used to even out dielectric stresses around the conductor. An insulation shield is a nonmagnetic metallic material applied over insulated conductor(s) to confine the electric field to the insulation. A bare cop- per shield surrounds the insulation shield, is typically grounded at each end, and grounded at splices to reduce shock hazards.
Use of Medium Voltage Cables:
Medium-voltage cables are used in industrial and commercial applications such as feeder and branch circuits for electric utility service, in wet, damp, or dry locations, in raceways, in underground ducts, direct buried, and in messenger systems in industrial and commercial utilities.
Limited Production of Medium Voltage Cables:
Because of their unique construction and voltage ratings, medium-voltage cables must only be terminated by following the manufacturer’s specific instructions. This typically involves the use of specialized electrical tapes and other components. Procedural requirements may include grounding the copper shield, chamfering the insulation to reduce voltage stress, and taping the conductors to prevent air pockets where ionizing air can deteriorate the insulation. Special training is generally required to make medium voltage cable splices and terminations.