Journeyman Electrician Practice Exam 2025 – The All-In-One Guide to Exam Success!

To determine the minimum size THW (Thermoplastic High Water Resistant) copper branch-circuit conductor needed for a 3-phase, continuous-duty AC motor with a full-load current of 70 amperes, several factors must be considered.

For motor circuits, the National Electrical Code (NEC) provides guidelines for the sizing of conductors based on full-load current ratings. According to NEC Article 430, the minimum conductors must often be sized according to the motor's full-load current and then adjusted for the type of insulation and ambient temperature.

The NEC specifies that for motors, the conductor may be sized based on a percentage of the full-load current, and typically a derating factor may be applied based on continuous operation. For continuous loads, conductors should be sized at 125% of the motor's full-load current.

Calculating for this motor:

- Full-load current = 70 amperes

- For a continuous load, the required current = 70 A x 1.25 = 87.5 amperes.

Now, looking at the wire gauge options available, 3 AWG copper conductors can safely carry 100 amperes according to NEC ampacity charts, which means it can adequately handle the calculated requirement for