The T4 classification specifies that electrical devices must operate with a maximum surface temperature of no more than 135°C. Products with a T6 rating are applicable across various temperature groups, whereas T4 devices are compatible with T4, T3, T2, and T1 conditions.
| Temperature Classification for Electrical Equipment | Maximum Permissible Surface Temperature of Electrical Equipment (°C) | Gas/Vapor Ignition Temperature (°C) | Applicable Equipment Temperature Class |
|---|---|---|---|
| T1 | 450 | ＞450 | T1~T6 |
| T2 | 300 | ＞300 | T2~T6 |
| T3 | 200 | ＞200 | T3~T6 |
| T4 | 135 | ＞135 | T4~T6 |
| T5 | 100 | ＞100 | T5~T6 |
| T6 | 85 | ＞85 | T6 |
The reason T6 is not typically used is that many devices, particularly those requiring high power or consisting of purely resistive circuits, are unable to achieve the stringent low-temperature conditions stipulated by the T6 classification.
