Regarding the 240.92(B) Calculations

40°C is more reasonable than 75°C for the

"Correction Factor for Temperature" calculations in 240.92(B).

Actual Reasonable Operating Temperatures of Current Carrying Conductors

The following are reasonable operating temperatures for current-carrying conductors based on the insulation type:

Thermoplastic Insulation (e.g., THHN, THWN)

75°C

Cross-Linked Polyethylene (XLPE)

90°C

Ethylene Propylene Rubber (EPR)

90°C

Silicone Rubber

125°C

Teflon (PTFE)

250°C

Note

These temperatures are based on the conductor's rated ampacity and may vary depending on the ambient temperature, conductor type, and installation method. Always refer to the manufacturer's specifications and local codes for specific requirements.

Additional Considerations



Ambient Temperature

The ambient temperature of the environment where the conductors are installed can affect their operating temperature.

Conductor Spacing

Closely spaced conductors can increase the operating temperature due to reduced heat dissipation.

Overloading

Overloading the conductors can lead to excessive heating and damage.

Conclusion: For 240.92(B) calculations, 40°C is a more reasonable value than 75°C. Actual reasonable operating temperatures for current-carrying conductors vary depending on the insulation type, but generally range from 75°C to 125°C. Flag for review