Understanding electric motor insulation & temperature 

By on

Anyone specifying or using electric motors should have a basic understanding how the insulation is related to temperature. Three classes of insulation are in common use (with 'F' being the most common):

  • class B - with a maximum operating temperature of 130 oC
  • class F - with a maximum operating temperature of 155 oC
  • class H - with a maximum operating temperature of 180 oC

The image (which is form an ABB catalogue for their low voltage performance motors), shows how temperature rise is distributed across the insulation.

Typically motors are designed for a maximum ambient temperature of 40 oC.

The difference between the average winding temperature and any hot spot is limited and it is usual to allow a 10 oC margin for class 'B' and 'F' insulation and a 15 oC margin for class 'H'.

Considering the ambient temperature and hot spot allowance gives the maximum temperature rise within which the motor must be designed to operate (105 oC for class 'F' for example).

When specifying (buying) a motor there are a couple of options. An insulation class could be specified and the motor specified as designed to run within that class. Alternatively the motor could be specified for an insulation class, but be design to run at a low class (for example insulation class 'F', temperature rise 'B').

The advantage of the second method is that there is an inherent 25 oC safety margin - useful if you are in a region with high ambient temperatures or need to date the motor for some other reason. Running motors at a reduced temperature will also significantly extend the useful life.



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



Latest Questions:

  1. current transformer
  2. MCCB Selection
  3. Electrtical Relay
  4. Arc flash calculator
  5. Current on each phase
  6. Current for each phase
  7. RCD OR Earth Leakage Unit tripping
  8. POWER

most popular notesMost Popular Notes:







newsletter logo

Our Newsletter

Receive updates on new posts by email
down arrow

Electric Power Distribution Engineering, Third Edition
Electric Power Distribution Engineering, ...
Turan Gonen
Hardcover - 1061 pages
$104.97
Solar Energy: The Physics and Engineering of Photovoltaic Conversion, Technologies and Systems
Solar Energy: The Physics and Engineering ...
Olindo Isabella, ...
Kindle Edition - 488 pages
Solar Electricity Handbook - 2015 Edition: A simple, practical guide to solar energy - designing and installing solar PV systems.
Solar Electricity Handbook - 2015 Edition: ...
Michael Boxwell
Paperback - 204 pages
$17.43
Electrical Power System Essentials
Electrical Power System Essentials
Pieter Schavemaker, ...
Hardcover - 340 pages
$81.70
Solar PV Engineering and Installation: Preparation for the NABCEP PV Installation Professional Certification
Solar PV Engineering and Installation: ...
Sean White
Paperback - 248 pages
$37.60
Energy Storage in Power Systems
Energy Storage in Power Systems
Francisco ...
Hardcover - 312 pages
$121.69
Renewable and Efficient Electric Power Systems
Renewable and Efficient Electric Power ...
Gilbert M. Masters
Hardcover - 712 pages
$102.30
Submarine Power Cables: Design, Installation, Repair, Environmental Aspects (Power Systems)
Submarine Power Cables: Design, ...
Thomas Worzyk
Paperback - 296 pages
$189.00
Electric Power Substations Engineering, Third Edition (Electrical Engineering Handbook)
Electric Power Substations Engineering, ...
Hardcover - 536 pages
$149.95
Solar Electric Power Generation - Photovoltaic Energy Systems: Modeling of Optical and Thermal Performance, Electrical Yield, Energy Balance, Effect on Reduction of Greenhouse Gas Emissions
Solar Electric Power Generation - ...
Stefan C.W. Krauter
Hardcover - 217 pages
$112.67
Solar Electricity Handbook - 2014 Edition: A Simple Practical Guide to Solar Energy - Designing and Installing Photovoltaic Solar Electric Systems
Solar Electricity Handbook - 2014 Edition: ...
Mr Michael Boxwell
Paperback - 200 pages
Solar Energy Engineering, Second Edition: Processes and Systems
Solar Energy Engineering, Second Edition: ...
Soteris A. Kalogirou
Hardcover - 840 pages
$99.96
Large-Scale Solar Power Systems: Construction and Economics (Sustainability Science and Engineering)
Large-Scale Solar Power Systems: ...
Dr Peter Gevorkian
Paperback - 400 pages
$72.74
Electric Energy: An Introduction, Third Edition (Power Electronics and Applications Series)
Electric Energy: An Introduction, Third ...
Mohamed A. El-Sharkawi
Hardcover - 606 pages
$106.40
The Guide to Photovoltaic System Installation (Explore Our New Electrical Trades 1st Eds.)
The Guide to Photovoltaic System ...
Gregory W Fletcher
Paperback - 384 pages
$66.60
Large-Scale Solar Power System Design (GreenSource Books): An Engineering Guide for Grid-Connected Solar Power Generation (McGraw-Hill's Greensource)
Large-Scale Solar Power System Design ...
Peter Gevorkian
Hardcover - 704 pages
$94.72
Solar Photovoltaic Basics: A Study Guide for the NABCEP Entry Level Exam
Solar Photovoltaic Basics: A Study Guide ...
Sean White
Paperback - 168 pages
$32.25
Photovoltaic Design and Installation For Dummies
Photovoltaic Design and Installation For ...
Ryan Mayfield
Paperback - 384 pages
$16.99
Independent Energy Guide: Electrical Power for Home, Boat, & RV
Independent Energy Guide: Electrical Power ...
Kevin Jeffrey
Paperback - 280 pages
Power System Monitoring and Control
Power System Monitoring and Control
Hassan Bevrani, ...
Hardcover - 288 pages
$119.00
Power Conversion and Control of Wind Energy Systems
Power Conversion and Control of Wind Energy ...
Bin Wu, Yongqiang ...
Hardcover - 480 pages
$121.06
Solar Photovoltaic Basics: A Study Guide for the NABCEP Entry Level Exam
Solar Photovoltaic Basics: A Study Guide ...
Sean White
Paperback - 168 pages
$32.25
Do It Yourself 12 Volt Solar Power, 2nd Edition (Simple Living)
Do It Yourself 12 Volt Solar Power, 2nd ...
Michael Daniek
Paperback - 128 pages
$13.70
Energy Systems Engineering: Evaluation and Implementation, Second Edition
Energy Systems Engineering: Evaluation and ...
Francis Vanek, Louis ...
Hardcover - 672 pages
Photovoltaic Systems Engineering, Third Edition
Photovoltaic Systems Engineering, Third ...
Roger Messenger, Amir ...
Hardcover - 528 pages
$103.66
Renewable and Efficient Electric Power Systems
Renewable and Efficient Electric Power ...
Gilbert M. Masters
Hardcover - 680 pages
Smart Power Grids 2011 (Power Systems)
Smart Power Grids 2011 (Power Systems)
Hardcover - 696 pages
$299.00
Power Electronics for Modern Wind Turbines (Synthesis Lectures on Power Electronics)
Power Electronics for Modern Wind Turbines ...
Frede Blaabjerg, Zhe ...
Paperback - 120 pages
$29.55
Power System Relaying
Power System Relaying
Stanley H. Horowitz, ...
Hardcover - 398 pages
$130.77


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