Final answer:
Conductors larger than 4/0 AWG are expressed in circular mils, marking the transition from the AWG system to a measurement based on the cross-sectional area of the wire.
Step-by-step explanation:
Conductor sizes for round wires made of conducting material are expressed in the American Wire Gauge (AWG) system, which standardizes wire sizes for consistency in electrical wiring and equipment. In the AWG system, the size of wires goes down as the gauge number increases, meaning that a larger gauge number indicates a smaller wire diameter. The question seeks to identify at which point conductor sizes shift from being described in AWG to being measured in circular mils.
The answer is that conductors larger than 4/0 AWG are expressed in circular mils. This threshold is right after the largest standard AWG size, which is 4/0 AWG. Sizes beyond this point are too large for the AWG scale and are instead measured in circular mils, a unit that represents the area of a circle with a diameter of one mil (one thousandth of an inch).