What is the smallest conductor size that can be installed from a 120/240-volt panelboard for a motor feeder?

For a motor feeder fed from a 120/240-volt panelboard, it is important to choose the appropriate conductor size to ensure safe operation and compliance with the National Electrical Code (NEC) requirements. The correct choice is based on factors such as motor load, allowable ampacity, and the type of insulation used.

The smallest allowable conductor size for a motor feeder generally corresponds to the maximum load it must carry and is based on calculations that consider the motor's full-load current. For most applications, the conductor must also account for the type and size of the circuit breaker or fusible disconnect protecting the motor.

A conductor size of 4/0 AWG is typically designed for substantial electrical loads. It provides adequate ampacity to handle considerable motor loads under typical operating conditions. Furthermore, the sizing must include considerations for factors such as ambient temperature, number of conductors, and the installation conditions, which can affect the ampacity.

In contrast, the other conductor sizes listed may not meet the minimum ampacity requirements needed for typical motors operating at this voltage level. Conductors that are too small can lead to overheating, increased resistance, and potential failure to handle the starting surges common with motors. Thus, 4/0 AWG represents a