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Conductors

Nov 30, 1995 12:00 PM

Included in this category are insulated power, control, aerial, and plenum cables, armored cables, instrumentation and communication cables, busway, busbars, feedrail, cablebus, bare and jacketed grounding wire, and all types of heating cable.

Typically, the term "wire" is used to describe the smaller AWG (American Wire Gauge) sizes of conductors, while larger ones in the kcmil (thousand circular mil) sizes are referred to as "cable." Manufactured assemblies of insulated conductors grouped together in many different configurations within an overall jacket are also called cables. Voltage ratings for power wire and cable include LV (low voltage) for 120V through 600V applications. Here, the insulation is rated for 600V. For application voltages from 601V through 35kV, MV (medium voltage) cables are used. Depending on the application voltage, the cable voltage ratings can be Sky, 15kV, and 35kV.

Wire and cable components

Copper is the most common element used as the current-carrying part of wire or cable. Its mechanical and electrical properties make it an ideal medium for conducting electrical power. Aluminum is often used in place of copper for power distribution because its lighter weight allows for easier handling. Copper-clad aluminum conductors are primarily used in communications.

The majority of general purpose building wire (600V) uses insulating materials that are members of the thermoses family (crosslinked polyethylene or rubber, for example) or the thermoplastic family (polyvinyl chloride, for example). Temperature ratings of these insulations range from 60 [degrees] C to 90 [degrees] C. Other specialized insulation types are rated at 250 [degrees] C for applications at higher temperatures.

Medium voltage cables have insulation systems rated at 90 [degrees] C, thus the Type MV-90 rating is given to them. These cables use copper tape or concentric wire strand for shielding systems. One construction utilizes corrugated drainwires embedded in its semiconducting jacket.

Cable types and applications

Metalclad (Type MC), armored (Type AC), mineral insulated (Type MI), nonmetallic (Type NM), service entrance (Type SE), underground feeder (Type UF), tray cable (Type TC), and many other types of low voltage cables are in everyday use in residential, commercial, institutional, and industrial facilities.

Power cable is used to carry large blocks of power. Generally, it is installed as single conductors in raceway, as direct-buried cable, as multiconductor cable in trays, as preassembled aerial cable supported from messenger wire, or as a metallic armored construction for additional protection. Cross-linked polyethylene (XLP) or ethylene-propylene rubber (EPR) insulation materials are normally used with this class.

Control cable, as well as data, communication, and instrumentation cable are specialized items intended to meet specific needs. Twisted-pair and coaxial cable are used extensively, with many variations in construction to meet specific needs of the installation. Here, insulation systems, shielding, and cable configurations are varied.

Freeze protection, maintenance of flow of viscous fluids, snow melting, and similar tasks are handled by the application of heating cable. A specialized form of cable, it has a heating element that is either a high-resistance wire or a semiconducting material. Depending on the watts-per-ft requirements, thermoplastic or Type MI cable is used. Armored types are applied in hazardous locations.

Another type of electrical conductor is busway, which includes feeder, lighting, trolley busways, and other specialized forms. Feeder busway can be used for service entrances, can be ventilated or nonventilated, mounted vertically or horizontally, and can have provisions for insertion of plug-in devices. These can be fused or unfused switches, circuit breakers, ground detectors, capacitors, or transformers constructed especially for direct mounting. The current medium in busway may be copper or aluminum, insulated or bare.

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