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How many classes have their temperatures above 150°C?
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In electrical engineering, insulation materials are categorized into specific classes based on their thermal stability. According to the standard IS 1271 (IEC 60085), there are exactly three classes with a temperature rating greater than 150°C: Class H (180°C), Class C (200°C), and Class C (220°C and above).
In electrical engineering, insulation materials are categorized into specific classes based on their thermal stability. According to the standard IS 1271 (IEC 60085), there are exactly three classes with a temperature rating greater than 150°C: Class H (180°C), Class C (200°C), and Class C (220°C and above).
Tmax>150°C — Criteria for High-Temperature Insulation Classes
The thermal classification of insulation materials defines the maximum allowable operating temperature for electrical equipment to ensure a reasonable life span of the dielectric properties. As temperature increases, chemical degradation of insulating materials accelerates following the Arrhenius law. The standard identifies classes F(155°C), H(180°C), and C(>180°C) as the high-temperature categories.
Class F is rated at 155°C, which is often considered the threshold for high-temperature applications.
Class H is rated at 180°C.
Class C encompasses all materials with ratings above 180°C (e.g., 200°C, 220°C, 250°C).
Total classes with ratings > 150°C are F, H, and C.
Higher power density in machines
Increased resistance to thermal overload
Increased cost of materials
Higher cooling requirements
Traction motors
High-temperature transformers
Aerospace electrical systems
The standard classification is A, E, B, F, H, and C.
Classes A(105°C), E(120°C), and B(130°C) are all below the 150°C threshold.
Option A, B, and C are incorrect as they do not match the standard count of recognized high-thermal insulation classes.
D is correct — There are three classes of electrical insulation (F, H, and C) that have thermal ratings exceeding 150°C.
Always verify thermal ratings using the IEC 60085 standard tables, as many exams specifically test the numerical limits for Class F, H, and C insulation.