The smallest feeder conductors permitted to be installed between the 120/240-volt, 3Ø, 4-wire panel and the gutter are what AWG or kcmil size?

The correct response of 250 kcmil (thousands of circular mils) as the smallest feeder conductor size for a 120/240-volt, 3-phase, 4-wire panel is based on National Electrical Code (NEC) guidelines. According to NEC, the sizes of conductors are determined by the amount of current they need to safely carry, considering factors such as the length of the run, ambient temperature, and whether they are installed in conduit or cable.

In this specific case, for a three-phase system, there are specific ampacity requirements for the feeder conductors, which vary based on the load and type of installation. The 250 kcmil conductors are often recognized for their suitability to handle significant current loads while providing adequate safety margin and performing according to established guidelines. This is particularly true when considering the installation of feeders that will be required to operate safely without overheating under full load conditions.

While other sizes could potentially be considered for different installations or higher capacity loads, the 250 kcmil size is determined to meet the minimum requirements for this application under NEC standards, ensuring that the electrical system operates efficiently and safely.