What minimum size aluminum wire is needed for a 440-volt, 3-phase branch circuit supplying a 60-ampere load at 325 feet?

To determine the minimum size aluminum wire needed for a 440-volt, 3-phase branch circuit supplying a 60-ampere load over a distance of 325 feet, we can apply the principles outlined in the National Electrical Code (NEC) and consider the factors of ampacity, voltage drop, and wire material.

For a 3-phase circuit, the voltage drop is a critical consideration, especially over long distances. The NEC provides guidelines for acceptable voltage drop levels, which is typically recommended to be no more than 3% for branch circuits.

First, we need to calculate the voltage drop using the formula for a 3-phase system, which is often expressed as:

[

\text{Voltage Drop (V)} = \frac{1.732 \times I \times L \times R}{1000}

]

Where:

• (I) is the current in amperes (60 A in this case).

• (L) is the one-way length in feet (325 ft).

• (R) is the resistance of the wire per 1000 feet, which varies based on the wire size.

For aluminum wire, the resistance per 1000 feet varies with gauge size. As wire size increases