Final answer:
Feeders with a common neutral are permitted by the NEC to supply both residential and industrial areas, making use of shared neutral conductors practical in various electrical installation scenarios.
Step-by-step explanation:
The National Electrical Code (NEC) outlines comprehensive rules for electrical wiring and installations, including the requirements for feeders containing a common neutral. According to the NEC, feeders with a common neutral can indeed supply both residential and industrial areas, as they are not limited to one specific type of occupancy or area. Therefore, the correct answer to the student's question is:
c) Both residential and industrial areas
Feeders that contain a common neutral, also known as a shared or multipurpose neutral, are commonly used in scenarios where multiple circuits are present, and it is beneficial to use one neutral conductor instead of individual neutrals for each circuit. This is often seen in both residential and industrial installations where it can help reduce the amount of wiring needed and simplify the overall electrical system design. However, care must be taken to ensure that the common neutral is adequately sized and protected to safely handle the return currents from all the circuits it serves.