What ampacity would be appropriate for three 1/0 AWG THW aluminum conductors in rigid metal conduit at 86 degrees F?

To determine the appropriate ampacity for three 1/0 AWG THW aluminum conductors in rigid metal conduit at a temperature of 86 degrees Fahrenheit, it is essential to reference the National Electrical Code (NEC) tables, particularly Table 310.16, which specifies the allowable ampacities of conductors based on their insulation type, number of conductors, and ambient temperature.

For 1/0 AWG aluminum conductors with THW insulation, the base ampacity at 30 degrees Celsius (86 degrees Fahrenheit) is typically about 130 amperes when installed in a single conduit. However, it is important to adjust for the number of conductors in the conduit, as the ampacity must be derated.

When three conductors are run together, the NEC requires a derating factor. For three conductors, you would apply a 70% derating factor. Thus, you calculate the derated ampacity as follows:

1. Start with the base ampacity: 130 A.

2. Apply the derating factor: 130 A x 0.7 = 91 A approximately.

However, this does not match the provided answers, indicating that an alternative adjustment or a common reference value might be considered