504.10 Equipment Installation
A simple apparatus, whether or not shown on the control drawing(s), shall be permitted to be installed provided the simple apparatus does not interconnect intrinsically safe circuits.
Informational Note No. 1: The control drawing identification is marked on the apparatus.
Informational Note No. 2: Associated apparatus with a marked Um of less than 250 V may require additional overvoltage protection at the inputs to limit any possible fault voltages to less than the Um marked on the product.
- Reference to Table 504.10(D)
- Calculation using the following equation:
|Po||=||output power marked on the associated apparatus or intrinsically safe apparatus|
|Rth||=||thermal resistance of the simple apparatus|
|Tamb||=||ambient temperature (normally 40°C) and reference Table 500.8(C)|
In addition, components with a surface area smaller than 10 cm2 (excluding lead wires) may be classified as T5 if their surface temperature does not exceed 150°C.
Table 504.10(D) Assessment for T4 Classification According to Component Size and Temperature
|Total Surface Area Excluding Lead Wires||Requirement for T4 Classification|
|<20 mm2||Surface temperature ≤275°C|
|≥20 mm2 ≤10 cm2||Surface temperature ≤200°C|
|≥20 mm2||Power not exceeding 1.3 W*|
|*Based on 40°C ambient temperature. Reduce to 1.2 W with an ambient of 60°C or 1.0 W with 80°C ambient temperature.|