When nine 4 AWG THW aluminum conductors are installed with three 8 AWG copper conductors, what is the ampacity of the circuit conductors?

To determine the ampacity of the circuit conductors when mixing different sizes and types of conductors, we need to consider the calculations based on the National Electrical Code (NEC) guidelines.

In this scenario, we have nine 4 AWG aluminum conductors, which have a specific ampacity rating according to NEC tables. For 4 AWG aluminum conductors, the ampacity typically falls into the range of 70 to 85 amperes, depending on the specific conditions such as ambient temperature and installation method.

However, since the installation includes 8 AWG copper conductors as well, which also have a specific ampacity classification, we must address the interaction between them as defined by NEC or any applicable derating rules. The 8 AWG copper conductors typically have an ampacity of around 40 to 55 amperes depending on the same conditions mentioned earlier.

When both types of conductors are installed together, and assuming they may have some impact on each other’s ampacity due to factors like grouping and potential temperature increases, we typically take the lower ampacity of the mixed types into consideration for setting the circuit's capacity.

Under these circumstances, if we assume that necessary adjustments for the conductors' physical properties and their