1.1 This specification covers bare concentric-lay-stranded conductors made from round copper wires, either uncoated or coated with tin, lead, or lead alloy for general use for electrical purposes. These conductors shall be constructed with a central core surrounded by one or more layers of helically laid wires. Note 1This specification also permits conductors for use as covered or insulated electrical conductors. Note 2Sealed conductors, that are intended to prevent longitudinal water propagation and are further covered/insulated, are also permitted within the guidelines of this specification. 1.2 For the purposes of this specification, conductors are classified as follows (Explanatory NOTE 1 and NOTE 2): 1.2.1 Class AAFor bare conductors usually used in overhead lines. 1.2.2 Class AFor conductors to be covered with weather-resistant (weather-proof), slow-burning materials, and for bare conductors where greater flexibility than is afforded by Class AA is required. 1.2.3 Class BFor conductors to be insulated with various materials such as rubber, paper, varnished cloth, and so forth, and for the conductors indicated under Class A where greater flexibility is required. 1.2.4 Class C and Class DFor conductors where greater flexibility is required than is provided by Class B conductors. 1.3 The SI values for density are regarded as the standard. For all other properties, the inch-pound values are to be regarded as standard and the SI units may be approximate.