A 4-inch square metal box with a plaster ring contains: two 12 AWG hots entering and spliced, one 12 AWG neutral entering and spliced, one 12 AWG equipment grounding conductor, one cable connector clamp inside the box, and one single-pole switch on a yoke. Using NEC 314.16(B), what is the total box fill volume in cubic inches?
Worked answer
Answer: B. 15.75 in³
Use the Table 314.16(B)(1) allowance for 12 AWG, 2.25 in³. Three conductors entering the box (two hots and one neutral) = 3 × 2.25 = 6.75 in³ [314.16(B)(1)]. All internal cable clamps together = one allowance, 2.25 in³ [314.16(B)(2)]. The switch yoke = two allowances, 4.50 in³ [314.16(B)(4)]. The equipment grounding conductor = one allowance, 2.25 in³ [314.16(B)(5)]. Total: 6.75 + 2.25 + 4.50 + 2.25 = 15.75 in³.
Reference: NEC 314.16(B)(1)-(5), Table 314.16(B)(1) (2023 NEC section numbers; check the edition your exam uses).
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