IEC 60228 is the International Electrotechnical Commission

International Electrotechnical Commission

The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

's international standard

International standard

International standards are standards developed by international standards organizations. International standards are available for consideration and use, worldwide...

 on conductors of insulated cables.

Among other things, it defines a set of standard wire cross-sectional areas:

International standard wire sizes (IEC 60228)
0.5 mm2	0.75 mm2	1 mm2	1.5 mm2	2.5 mm2	4 mm2
6 mm2	10 mm2	16 mm2	25 mm2	35 mm2	50 mm2
70 mm2	95 mm2	120 mm2	150 mm2	185 mm2	240 mm2
300 mm2	400 mm2	500 mm2	630 mm2	800 mm2	1000 mm2

In engineering applications, it is often most convenient to describe a wire

Wire

A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

 in terms of its cross-section area, rather than its diameter

Diameter

In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

, because the cross section is directly proportional to its strength and weight, and inversely proportional to its resistance

Electrical resistance

The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...

. The cross-sectional area is also related to the maximum current that a wire can carry safely.

This document is one considered Fundamental in that it does not contain reference to any other standard.

Class

This refers to the flexibility of a conductor

• Class 1: Solid conductor
• Class 2: stranded conductor intended for fixed instalation
• 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&6: Maximum diameter of any component strand of the conductor

Resistance

The required maximum resistance (in ohms/km)of each conductor size, class and type (both plain copper and metal coated)

History

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 4mm² conductor from two different suppliers may have different resistance values. Instead this document describes conductors by their nominal size.

Nominal Size

This is the size of a conductor determined by its resistance rather than its physical dimensions. This is a key distinction as it makes a standardised definition of conductors based solely on their electrical characteristics.

Almost all characteristics of conductors, resistance, current carrying capacity etc are independent of 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.

See also

• American wire gauge
  American wire gauge
  American wire gauge , also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire...
  
  
• British Standard Gauge
  Standard wire gauge
  British Standard Wire Gauge is a set of wire sizes given by BS 3737:1964 , and is generally abbreviated to SWG. It is also known as: Imperial Wire Gauge or British Standard Gauge. Use of SWG sizes has fallen greatly in popularity, but is still used as a measure of thickness in guitar strings and...
  
  
• Wire gauge comparison chart