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Conductor classes - some homework learning

From solid to stranded - what are conductor classes?

The below is a guide only - there may be application or site specifics that require a different approach to those outlined below.

So, let's start at the beginning

1. What is a CONDUCTOR?

It is an insulated or uninsulated wire or bundle of wires and consisting of one single or more wires used to transmit electrical energy or signals.

2. What are the materials used in CONDUCTOR?

The material should be selected according to the usage and purpose of the cable.


Low voltage indoor installation cables: Copper,

Low voltage and medium voltage energy cables: Copper or aluminium,

High voltage underground and submarine cables: Copper or aluminium,

High voltage overhead line cables: Steel-core aluminium conductors are used.

3. What is the conductor class?

IEC60228 (The Electrotechnical Commission's international Standard on conductors of insulated cables) defines a set of standard cross-sectional areas as well as other standards, including the class, size and resistance.

There are 4 main conductor classes, referring to the flexibility and thermal effects of a conductor.

  • Class 1: Solid conductor

  • Class 2: Stranded conductor intended for fixed installation

  • Class 5: Flexible conductor

  • Class 6: Very Flexible conductor


The nominal 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


The maximum permissible resistance (in ohms per kilometre) of each conductor size, class and type (both plain copper and metal coated)

These 3 elements are important, as not all copper has the same resistivity value, meaning a 2.5mm" conductor from 2 different manufacturers could have very different resistance values. IEC60228 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 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.

The table below shows the basic comparison of different categories of copper conductors

In short, the more flexible a cable needs to be, the more strands there will be in the conductors.

It is also important to understand how the different conductors work alongside various terminals/termination methods, as these often differ for solid conductors vs stranded.

We at Jigsaw Controls have standardised on the use of Class 5 Tri-rated wiring for all our panel wiring, allowing for the greatest flexibility in all applications.

Any questions or queries, or to enquire how we can help with your wiring projects - get in touch today!

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