What is the minimum ampacity requirement for the neutral conductor of a 3-wire branch circuit supplying a household electric range?

The correct choice reflects the National Electrical Code (NEC) requirements for the neutral conductor in a residential 3-wire branch circuit that supplies an electric range. According to NEC guidelines, the minimum ampacity for the neutral conductor should be calculated based on the maximum demand of the circuit. This is typically set at 70 percent of the branch-circuit rating when dealing specifically with an electric range.

In circuits supplying residential equipment like household electric ranges, the neutral conductor is often subject to specific load considerations. An electric range usually has elements that operate on single-phase power, and the load is not always balanced, resulting in the neutral carrying considerable current. Therefore, sizing the neutral conductor at 70 percent of the branch-circuit rating provides adequate current-carrying capacity while ensuring safety and preventing overheating.

Other options suggest different percentages that do not meet the NEC guidelines for residential ranges. Choosing an ampacity lower than 70 percent might not adequately account for the potential unbalanced load, while higher percentages would unnecessarily increase the conductor size beyond what is needed for safe operation. Thus, adhering to the 70 percent rule ensures compliance with safety standards and provides reliable performance of the electrical system.