There are basically four classes of insulation a b f and h class f being the most commonly used.
Which insulation class is better f or h.
1800 hours with class b insulation.
Class a is an older form of insulation utilizing organic varnishes and resins available many years ago.
Average winding temperature rise.
Hot spot temperature rise.
Each insulation class has a margin allowed to compensate for the motor s hot spot.
These insulation classes were established to meet motor temperature requirements found in industrial applications.
Insulation class b f h maximum winding temperature 130 c 155 c 180 c 0 40 120 130 155 145 165 180 c 20 maximum ambient temperature minimum ambient temperature 30 minimum ambient temperature 10k 105k 40 c class f b 155 c 80k safety margin 25k 150 c ptcs setting 2 c0 2 c0 2 c0 regal beloit bv mors 2.
Nema insulation classes do away with guessing and give the motor manufacturer a defined framework to operate in.
Other materials or combinations of materials may be included in this class if by experience or tests they can be shown to be capable of operation at temperatures above the class h limit.
The electrical insulation system is sometimes referred to as insulation class or thermal classification the different classes are defined by nema underwriters laboratories ul and iec.
Example a motor operating at 180 o c will have an estimated life of.
As can be seen from the above table hot spot over temperature allowance for a b f and h are respectively 5 c 10 c 10 c and 15 c.
The electrical insulation system for wires used in generators electric motors transformers and other wire wound electrical components is divided into different classes by temperature and temperature rise.
Moving from an insulation system class f with a hotspot of 140 c to a hotspot of 160 c the s9 ratings are able to be increased by 7 with an improvement in design of.
Similarly a class h system operating at a class f temperature rise will provide the same life expectancy as a class f system operating at a class b temperature rise.
8500 hours with class f insulation.
Only 300 hours with class a insulation.
Tens of thousands of hours with class h insulation.
The surface temperature of the motor is typically 30 c lower than it is at the windings.
So if we look at a class f insulated motor which will be happy running at 155 c and then subtract 30 c we get a surface temperature of 125 c.
The hot spot is a point at the center of the motor s windings where the temperature is higher.
