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Conductors Vocabulary Term Definition ambient temperature The nominal temperature of the air that surrounds devices and systems. Ambient temperature must be accounted for when selecting a conductor. American Wire Gage A system of units used to express conductor sizes and is a convenient system that uses whole numbers with clear relationships to each other. ampacity The allowable current-carrying capacity of a conductor measured in amps. CEC tables list maximum safe ampacities for each wire gage. area The amount of space, or number of square units, inside a closed figure. The crosssectional area of a wire is expressed in circular mils. busway Busway or bus duct, as it is sometimes called, is a system assembled from prefabricated sections. The sections provide plug-in openings at regular intervals for switches and tapoff devices. Because it is flexible and neat, it is ideal for factory production areas and school shop classrooms. cable A term generally used to describe larger conductor sizes. Cable is used to mean various things in the CEC, but its meaning is always clearly defined. circular mil The standard unit of a wire's cross-sectional area. Circular mils are expressed in mils squared. circular mil foot A standard unit of conductor volume used to make comparisons between different metals. One circular mil foot is equal to a wire 1 foot in length with an area of 1 circular mil. conductor A material or element that allows free movement of electrons and therefore allows easy flow of electricity. Most conductors are metals. conduit A pipe or liner used as a raceway to carry and protect conductors. cord A single conductor is made flexible by incorporating many fine strands of wire. When two or more flexible wires are run together in a single jacket, a flexible cord or cable is produced. Flexible cords are generally not allowed for permanent wiring. They are used for pendant and portable equipment that usually have attachment plugs. Various types of flexible cords and their conditions of use are listed in the CEC. correction factor Any variable condition that must be accounted for when selecting a wire size. Correction factors such as temperature, number of conductors, and conductor length influence allowable ampacity. derating A reduction in the ampacity of a conductor due to correction factors. Conductors are rated for a specific set of conditions, and when those conditions change, ampacity must be derated. dielectric The insulating material that separates conductors and the outer protective covering. Dielectrics are non-metallic. dielectric strength The voltage at which the insulating qualities of a material break down. fibrous braid A nonmetallic outer covering used to protect a conductor’s insulating material. Fibrous braid is the most common NM covering. impedance The resistance to current flow in an AC circuit. insulation A material that isolates conductive materials and helps to correctly channel electricity. Most wires are covered by insulation. Conductors Vocabulary Term Definition insulation resistance The resistance to current leakage through and over the surface of the material. Insulation resistance is one of two fundamental wire insulator properties. kcmil Abbreviation for a thousand circular mils. Kcmil is a unit used to express large conductor sizes. lead sheath A watertight metallic outer covering used to protect a conductor's insulating material. A lead sheath is a continuous jacket molded around the wire to seal it from any moisture damage. metallic armor A heavy-duty metallic outer covering used to protect a conductor's insulating material. Metallic armor is used in situations where a wire is exposed to physical wear and tear. mil A linear unit of diameter equal to 0.001 of an inch. The mil is used because wire diameters are often very small. Canadian Electrical Code The standard for minimum safe electrical installations. The CEC is adopted in some form as law in all Provinces. raceway An enclosed channel of metal or nonmetallic materials designed expressly for holding wires or cables. resistance The opposition to current flow. Resistance is measured in ohms. resistivity Also known as specific resistance, the measure of a material's natural resistance to current flow. Resistivity is the opposite of conductivity, so it follows that good conductors have low resistivity per circular mil foot. specific resistance Another term for resistivity. Every material has a set specific resistance per circular mil foot at a specific temperature. temperature coefficient A ratio of increased conductor resistance per degree Celsius rise in temperature. Most metals increase in resistance as temperature increases, giving them a positive temperature coefficient. tensile strength The maximum stress, or tension, a material can endure before it breaks. Tensile strength is usually expressed in pounds per square inch. thermoplastic A plastic that may be repeatedly heated, shaped, and cooled without damage. Thermoplastic is commonly used for wire insulation. voltage drop The reduction in voltage level from the source to the load caused by conductor resistance. volume The amount of space contained within a three-dimensional shape. The circular mil foot is a unit of conductor volume used to compare things such as specific resistance. wire A generic term, sometimes used interchangeably with conductor or cable, meaning any slender rope of drawn metal. The term "wire" is often used to include the insulation.