A residential building has a total of 30 lighting fixtures and 20 receptacle outlets. What is the minimum conductor size required for the feeder circuit, assuming a 120/240V, 3-phase system and a 0.7 service factor?
- A10 AWG
- B12 AWG
- 14 AWG
- D16 AWG
Exam tip
Always consider the service factor when determining the minimum conductor size.
Why C is correct
The minimum conductor size is determined by the maximum load and the NEC requirements. For lighting fixtures, the ampacity is 1.5A per fixture, and for receptacles, it is 1.5A per outlet. Total load = (30 fixtures * 1.5A) + (20 outlets * 1.5A) = 90A. With a service factor of 0.7, the required ampacity is 90A / 0.7 = 128.57A. The minimum conductor size for 128.57A is 14 AWG according to Table 310.16(B)(16).