INSULATION (TEMPERATURE) CLASSES
Various insulation materials are used in electric motors and each has its own function.
• Enamel wire insulation
• Slot and phase insulation materials (insulation between the winding and the stator
lamination pack and phase insulation between the windings heads).
• Winding impregnation.
• Insulating sleeve used to cover wire/lead connections.
• Insulation of winding leads (between the winding and the terminal board).
These materials are specified in thermal classes referenced as Y-A-E-B-F-H-C. Every thermal class has its own
temperature limit. Each material of a specific class needs to retain its mechanical and electrical properties within
the temperature limit.
-20°C
40°C
-20°C
40°C
-20°C
40°C
-20°C
40°C
-20°C
40°C
-20°C
40°C
6 0K
5K
Class A (105°C)
Class E (120°C)
Class B (130°C)
Class F (155°C)
75K
5K
8 0K
10K
10K
105K
15K
125K
Class H (180°C)
10K
180°C
130°C
120°C
105°C
25K
155°C
80K
0°C
-30°C
Class F/B
Ambient Temperature
Max Temperature rise
Hot Spot Margin
Safety Margin at Class F/B
Units:
°C - Degree Celsius
K - Kelvin (equal to Celsius)
The maximum permissible temperature rise of the winding is determined based on the thermal class temperature
limits. The temperature of the winding increases as a result of the copper and iron losses in the electric motor
during operation. The winding temperature rise is determined through measuring the winding resistance, which
increases with increasing temperature. To allow for any Hot Spots in winding lower temperature limits are
specified for the insulation materials.
Exico motors have been produced with insulation class F with winding temperature rise in accordance with the
class B (max 80K). This means that the motors have a temperature reserve of 25K. This reserve can be utilised for
short-term overload, a higher ambient temperature (above 40°C), for supply voltage/frequency fluctuation etc.
PTCs Thermistors setting for:
Insulation class F
Insulation class H
Exico Electric Motors Limited
4 Stanton Close
Finedon Road Industrial Estate
Wellingborough
NN8 4HN
United Kingdom
Alarm
145°C
170°C
Tripping
155°C
180°C
www.exico.co.uk
info@exico.co.uk
Tel. +44 (0)1933 277930