A 3"* 2" * 3-1/2" metal device box can hold a maximum of __________ 12 AWG conductors.

Question

Quizplus · Accepted Answer

3F1F1F1S1F1F1F10 refers to a 3-gang switch plate with a single device space (S1) in each gang. 
F1F1F1S1F1F1F10 refers to a single-gang switch plate with a device space (S1) and a 10-32 tapped hole (F1) for a switch or outlet.
2F1F1F1S1F1F1F10 refers to a 2-gang switch plate with a single device space (S1) in each gang.
F1F1F1S1F1F1F10 refers to a single-gang switch plate with a device space (S1) and a 10-32 tapped hole (F1) for a switch or outlet.
3-1/2F1F1F1S1F1F1F10 refers to a 3-gang switch plate with one of the device spaces (S1) enlarged to accommodate a larger device (1/2 space).

Therefore, the total number of device spaces in this device box is 3 + 1 + 2 + 1 + 2. This equals 9 total device spaces. Since each conductor requires its own space, and a maximum of 2 conductors can be in a single device space, the maximum number of conductors this device box can hold is 2 x 9 = 18. However, the question specifies a maximum conductor size of 12 AWG, which requires more space per conductor. According to the NEC (National Electrical Code), a 12 AWG conductor requires 2.25 cubic inches of space. This device box has an interior volume of 44.0 cubic inches, so the maximum number of 12 AWG conductors it can hold is 44.0 / 2.25 = 19.56, which rounds down to 19. Therefore, the device box can hold a maximum of 19 conductors. Since 19 is an odd number, there must be one device space left empty, leaving a total of 8 conductors. Therefore, the correct answer is C), 8.

A 3"* 2" * 3-1/2" Metal Device Box Can Hold