When calculating the ampacity of a common neutral conductor installed as part of a circuit for an outside feeder or branch circuit, the ampacity of the common neutral conductor shall comply with which of the following?
Note: This applies to lighting equipment installed outdoors.

  1. It shall always be the same size as the largest ungrounded phase conductor.
  2. The maximum net calculated load current between the neutral conductor and all ungrounded conductors connected to any one phase of the circuit.
  3. The maximum net calculated load current between the neutral conductor and the equipment grounding conductor.
  4. The minimum net calculated load current between the neutral conductor and all ungrounded conductors connected to any one phase of the circuit.


Answer: B

Article 225 covers the rules for installation of outside branch circuits and feeders. As noted in 225.7(B), "… the maximum net calculated load current between the neutral conductor and all ungrounded conductors connected to any one phase of the circuit." This applies to lighting equipment installed outdoors.

Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at necexpert@aol.com.