Temperature Class (T-Code) is a key parameter for explosion-proof electrical equipment. It indicates the equipment's maximum surface temperature, which must stay below the auto-ignition temperature (AIT) of surrounding hazardous substances.

1. Temperature Groups Table (IEC/ATEX)

For Dust: Usually marked with specific temperature (e.g. T135°C or T120°C) instead of T1–T6.

2. How to Select the Right T-Code

1. Find AIT of the substance (check MSDS/SDS or IEC 60079-20-1).
2. Apply Safety Margin: Equipment max surface temp must be lower than AIT. Recommend at least 20°C margin.
3. Example: AIT 155°C → Choose T4 or lower.

Common Examples:

• Hydrogen (AIT ≈560°C) → T1~T4 (T4 most common)
• Gasoline (AIT ≈280°C) → T3 or lower
• Diethyl ether (AIT ≈160°C) → T4 or lower
• Aluminum dust → Check specific limit (e.g. ≤135°C)

Marking Examples: Ex db IIC T4 Gb → Max surface ≤135°C (Gas). Ex tb IIIC T120°C Db → Max surface ≤120°C (Dust).

3. Important Notes

• Gas: Use T1–T6 classes. Dust: Use exact °C value.
• Standard ambient rating: -20°C to +40°C (special versions for extremes).
• Most Common: T5-T6 is widely used in oil & gas.

Quick Memory: T1 = Most lenient (450°C) → T6 = Most strict (85°C).