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 1 -This specification also permits conductors for use as covered or insulated electrical conductors. Note 2 -Sealed 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 AA - For bare conductors usually used in overhead lines. 1.2.2 Class A - For 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 B - For 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 D - For 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.