If conductors are installed in rigid metal conduit at an ambient temperature of 40°C, what is the correct ampacity for these insulated conductors?

To determine the correct ampacity of insulated conductors installed in rigid metal conduit at an ambient temperature of 40°C, one must refer to the National Electrical Code (NEC) and relevant ampacity tables, such as Table 310.15(B)(16). These tables provide the allowable ampacities for conductors based on several factors, including conductor type, size, and installation conditions.

At an ambient temperature of 40°C, the ampacity of conductors needs to be adjusted according to their temperature rating which is typically based on an ambient temperature of 30°C. This is where the correction factor comes into play. When the temperature increases from the standard reference temperature, the ampacity must be adjusted downwards.

In this specific scenario, the ampacity for the type of conductor being considered (for example, copper or aluminum conductors) can be found from the NEC tables. The adjustment for the temperature increase from 30°C to 40°C should yield a lower ampacity value compared to what is listed at 30°C. After accounting for this adjustment, one would arrive at the value of 186 A.

In this way, the correct choice reflects not only the initial ampacity of the conductor but also the necessary temperature correction that