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. The electrical insulation system is sometimes referred to as insulation class or thermal classification.
| Sl. No. | Insulation Class | Temperature | Materials Used |
| 1. | Y | 90°C | Cotton, Silk, Paper, Wood (without impregnation) |
| 2. | A | 105°C | Cotton, Silk, Paper, Wood (with impregnation) |
| 3. | E | 120°C | Wire, Enamel |
| 4. | B | 130°C | Mica, Asbestos, Glass fibre (with suitable clothing) |
| 5. | F | 155°C | Mica, Asbestos, Glass fibre (with suitable clothing) (can withstand 25°C extra temp.) |
| 6. | H | 180°C | Combination of Mica, Asbestos, Glass fibre |
| 7. | C | >180°C | Mica, Porcelain, Glass, Quartz with or without an inorganic binder |
