What is the minimum size STO cord for a motor supplied from a 120/240-volt, 3Ø, 4-wire panelboard?

To determine the minimum size for a Service Entrance (STO) cord for a motor supplied from a 120/240-volt, 3-phase, 4-wire panelboard, it’s essential to consider the requirements as dictated by the National Electrical Code (NEC) and motor application standards.

For a 3-phase motor operating under these voltage conditions, the minimum wire sizing is typically based on the motor’s full-load current (FLC) as well as the ampacity tables found in the NEC. When sizing conductors for 240-volt applications, such as a motor setup, the wire gauge must accommodate the current that will flow through it safely, minimizing voltage drop and ensuring the conductor can handle the motor's load.

The correct answer, which is size 4 wire for the conduit type identified (STO cord), is aligned with standard NEC guidelines. Conductors sized at 4 AWG copper are often suitable for higher ampacity requirements while remaining compliant with the safety standards set for motor applications. This sizing effectively balances the need for sufficient conductivity while managing heat dissipation and electrical performance.

Additionally, other options represent sizes that may either be too small to safely carry the expected current for many motor applications at this voltage and configuration. Proper