Question

One of the following does not represent a valid combination of ‘Class’ of insulating material and its limiting temperature in 'Degree Centigrade'.

1. ‘Class- A’ – 105°C
2. ‘Class- F’ – 155°C
3. ‘Class- H’ – 180°C
4. ‘Class- B’ – 120°C

Answer 1

Correct Answer - Option 4 : ‘Class- B’ – 120°C

Concept:

There are 7 class of insulating materials, each suitable for different application:

The permissible temperature limit at which the insulators may be worked safely without deterioration depends upon the type and class of the insulation as detailed below.

Class	Maximum temperature in °C
Class Y	Maximum temperature 90°C
Class A	Maximum temperature 105°C
Class E	Maximum temperature 120°C
Class B	Maximum temperature 130°C
Class F	Maximum temperature 155°C
Class H	Maximum temperature 180°C
Class C	Maximum temperature above 180°C (limited stability up to 225°C)