# 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.

More interesting Notes:

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

## Latest Questions:

### Most Popular Notes:

Electric Power Distribution Engineering, ...
Turan Gonen
Hardcover - 1061 pages
$104.97 Solar Energy: The Physics and Engineering ... Olindo Isabella, ... Kindle Edition - 488 pages Solar Electricity Handbook - 2015 Edition: ... Michael Boxwell Paperback - 204 pages$17.43
Electrical Power System Essentials
Pieter Schavemaker, ...
Hardcover - 340 pages
$81.70 Solar PV Engineering and Installation: ... Sean White Paperback - 248 pages$37.60
Energy Storage in Power Systems
Francisco ...
Hardcover - 312 pages
$121.69 Renewable and Efficient Electric Power ... Gilbert M. Masters Hardcover - 712 pages$102.30
Submarine Power Cables: Design, ...
Thomas Worzyk
Paperback - 296 pages
$189.00 Electric Power Substations Engineering, ... Hardcover - 536 pages$149.95
Solar Electric Power Generation - ...
Stefan C.W. Krauter
Hardcover - 217 pages
$112.67 Solar Electricity Handbook - 2014 Edition: ... Mr Michael Boxwell Paperback - 200 pages Solar Energy Engineering, Second Edition: ... Soteris A. Kalogirou Hardcover - 840 pages$99.96
Large-Scale Solar Power Systems: ...
Dr Peter Gevorkian
Paperback - 400 pages
$72.74 Electric Energy: An Introduction, Third ... Mohamed A. El-Sharkawi Hardcover - 606 pages$106.40
The Guide to Photovoltaic System ...
Gregory W Fletcher
Paperback - 384 pages
$66.60 Large-Scale Solar Power System Design ... Peter Gevorkian Hardcover - 704 pages$94.72
Solar Photovoltaic Basics: A Study Guide ...
Sean White
Paperback - 168 pages
$32.25 Photovoltaic Design and Installation For ... Ryan Mayfield Paperback - 384 pages$16.99
Independent Energy Guide: Electrical Power ...
Kevin Jeffrey
Paperback - 280 pages
Power System Monitoring and Control
Hassan Bevrani, ...
Hardcover - 288 pages
$119.00 Power Conversion and Control of Wind Energy ... Bin Wu, Yongqiang ... Hardcover - 480 pages$121.06
Solar Photovoltaic Basics: A Study Guide ...
Sean White
Paperback - 168 pages
$32.25 Do It Yourself 12 Volt Solar Power, 2nd ... Michael Daniek Paperback - 128 pages$13.70
Energy Systems Engineering: Evaluation and ...
Francis Vanek, Louis ...
Hardcover - 672 pages
Photovoltaic Systems Engineering, Third ...
Roger Messenger, Amir ...
Hardcover - 528 pages
$103.66 Renewable and Efficient Electric Power ... Gilbert M. Masters Hardcover - 680 pages Smart Power Grids 2011 (Power Systems) Hardcover - 696 pages$299.00
Power Electronics for Modern Wind Turbines ...
Frede Blaabjerg, Zhe ...
Paperback - 120 pages
$29.55 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