Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

NEMA Insulation Classes

Electrical insulation systems rated by standard NEMA classifications to maximize allowable operating temperatures.

Electrical insulation systems are rated by standard NEMA (National Electrical Manufacturers Association) classifications according to maximum allowable operating temperature:

 Temperature Tolerance Class Maximum Operation Temperature Allowed Allowable Temperature Rise at full load 1.0 service factor motor 1) Allowable Temperature Rise 1.15 service factor motor 1) oC oF oC oC A 105 221 60 70 B 130 266 80 90 F 155 311 105 115 H 180 356 125 -
• T(oF) = [T(oC)](9/5) + 32

1) Allowable temperature rises are based upon a reference ambient temperature of 40oC. Operation temperature is reference temperature + allowable temperature rise + allowance for "hot spot" winding.

Example Temperature Tolerance Class F:

40 oC + 105 oC + 10 oC

= 155 oC

In general a motor should not operate with temperatures above the maximum. Each 10 oC rise above the rating may reduce the motor lifetime by one half. It is important to be aware that insulation classes are directly related to motor life.

Example - a motor operating at 180oC will have an estimated life of

• only 300 hours with Class A insulation
• 1800 hours with Class B insulation
• 8500 hours with Class F insulation
• tens of thousands of hours with Class H insulation

Temperature Tolerance Class B is the most common insulation class used on most 60 cycle US motors. Temperature Tolerance Class F is the most common for international and 50 cycle motors.

Related Topics

• Electrical

Electrical engineering with units, amps and electrical wiring. Wire gauges, electrical formulas, motors and more.

Related Documents

• Dielectric Strength of Insulating Materials

The dielectric strength of a material is the ability to the material to act as an insulator.
• Electrical Motors - Frame Dimensions

Electrical motors NEMA frame dimensions.
• Electrical Motors - NEMA Frame Assignments

NEMA frame assignments.
• NEC - National Electrical Code

National Electrical Code.
• NEMA - National Electrical Manufacturers Association

National Electrical Manufacturers Association.
• NEMA Enclosure Standards for Electric Motors

NEMA enclosure standard for electrical motors.

Search

Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .

Citation

• The Engineering ToolBox (2004). NEMA Insulation Classes. [online] Available at: https://www.engineeringtoolbox.com/nema-insulation-classes-d_734.html [Accessed Day Month Year].

Modify the access date according your visit.

8.21.8

.