Feeders that contain a common neutral conductor are permitted to supply which of the following?

The correct choice highlights that feeders containing a common neutral conductor can supply either two or three sets of three-wire feeders. This is supported by the National Electrical Code (NEC), which allows for the use of a common neutral when specific conditions are met. In this context, the common neutral serves as the return path for the load currents from the phases of the system, effectively balancing the loads across multiple circuits.

When employing a common neutral, the configuration is important. With three-wire feeders, the common neutral can help manage the return currents effectively, reducing the risk of overloading any individual conductor. Additionally, when multiple sets of three-wire feeders are utilized, a properly sized common neutral conductor must be installed that can safely carry any unbalanced load that might occur.

This setup becomes particularly advantageous in multi-phase systems, as it promotes efficiency and reduces material costs associated with running multiple individual neutral conductors for each feeder, thus leveraging the common neutral while adhering to code requirements and safety standards.

The other options are narrower in scope or would not accommodate the flexibility that common neutrals allow in multi-wire systems, making the choice of two or three sets of three-wire feeders the most suitable answer.