Thermoplastic and Thermosetting Insulation 

By on

While there are a vast array of cable insulation materials, these are often divided into two general  types;  Thermoplastic or  Thermosetting.   For example the current capacity determination of a cable in accordance with  the UK Wiring Regulations is categorized into thermoplastic and thermosetting cables.

Thermoplastic materials are composed of chains of  molecules (polyethylene for example).  When heat is applied the energy will allow the bonds to separate and the material can flow (melt) and be reformed.

Thermosetting materials are formed when materials such as polyethylene undergo specific heating or chemical processes. During this process the individual chains become cross linked by smaller molecules making a rigid structure.    Thermosetting materials cannot reheated, melted and remolded.

While thermoplastic materials have the advantage of being able to be reformed, thermosetting materials are generally more heat resistance and have greater strength.

The operating temperature of any cable is an important parameter in determining the maximum allowable current.   While the actual temperature varies depending on the material used, the UK Wiring Regulations limits the choice in calculating the current rating to two temperatures only:

  • Thermplastic 70 0C
  • Thermosetting 90 oC

Note: more specific calculations based on actual material properties are allowed.  However, for ease of use most practical application will use 70 oC or 90 oC and the methods outlined in the regulations.

See Also



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus



MIT OpenCourseWare

MIT OpenCourseWare, makes the materials used in teaching all MIT subjects available on the Web, free of charge, to any user in the world.

Motor Insulation

Insulation on a motor prevents interconnection of windings and the winding to earth.  When looking at motors, it is important to understand how the insulation...

What is an Open Delta Transformer

In three phase systems, the use of transformers with three windings (or legs) per side is common.  These three windings are often connected in delta or...

IEC 61439 Verification Methods

The (relatively new) switchgear and control gear standard, IEC 61439 'Low-voltage switchgear and controlgear assemblies' has three methods which can be...

How to measure power supply quality

If your are ever called out to troubleshoot something on your electrical system, one of the first things consider is the supply voltage. You want to ensure...

Low Voltage Switchroom Design Guide

Low voltage (LV) switchrooms are common across all industries and one of the more common spatial requirements which need to be designed into a project...

Low Voltage Fault Tables

The following tables provide quick order of magnitude fault levels for a a range of typical low voltage situations.

Cable Insulation Properties

Cable insulation is used to provide electrical separation between conductors of  a cable.  During the historical development of cables, numerous types...

Fault Calculation - Symmetrical Components

For unbalance conditions the calculation of fault currents is more complex. One method of dealing with this is symmetrical components. Using symmetrical...

Frame Leakage Protection

While not as popular as it once was, frame leakage protection does still have some use in some circumstances.  In essence frame leakage is an earth fault...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note