Comparison of SWG (red),AWG (blue) and IEC 60228 (black)wire gauge sizes from 0.03 to 200 mm² to scale on a 1 mm grid – in the SVG file, hover over a size to highlight it
In engineering applications, it is often most convenient to describe a wire in terms of its cross-section area, rather than its diameter, because the cross section is directly proportional to its strength and weight, and inversely proportional to its resistance. The cross-sectional area is also related to the maximum current that a metallic wire can carry safely.
This document is one considered fundamental in that it does not contain reference to any other standard.
Description
The document describes several aspects of the conductors for electrical cables
Class
This refers to the flexibility and thermal effects i.e temperature of a conductor.
Class 1: Solid conductor
Class 2: Stranded conductor intended for fixed installation
Class 5: Flexible conductor
Class 6: Very Flexible conductor
Size
The nominal (see below) cross-sectional area for standard conductors including the following:
Class 2: Minimum number of strands required to make particular conductor size
Class 5 and 6: Maximum diameter of any component strand of the conductor
Resistance
The maximum permissible resistance per unit length (in ohms per kilometre – Ω/km) of each conductor size, class and type (both plain copper and metal coated)
Purpose of the document
This document and its precursors were created due to a need for a standard definition of cable conductor size. The main problem being that not all copper has the same resistivity value, so, for example, a 4 mm2 conductor from two different suppliers may have different resistance values. Instead this document describes conductors by their nominal size, determined by resistance rather than physical dimensions. This is a key distinction as it makes a standardized definition of conductors based solely on their electrical characteristics.
Almost all characteristics of conductors, resistance, current carrying capacity etc. are dependent on the physical dimensions of the conductor. However this document allows an easy reference whereby the standard conductor sizes and reference to physical dimensions are maintained but given an exact meaning in terms of the electrical characteristics of a conductor.
