A four-gang plastic device box contains three 3-way switches and one GFCI receptacle. Two 14/2 w/ground NM cables enter the box to bring power to the switches and send power to other devices along the circuit. Three 14/3 w/ground NM cables enter the box to terminate on the switches. Two 12/2 w/ground NM cables enter the box and terminate on the GFCI receptacle. What is the calculated volume fill of these devices and conductors?

A four-gang plastic device box contains three 3-way switches and one GFCI receptacle. Two 14/2 w/ground NM cables enter the box to bring power to the switches and send power to other devices along the circuit. Three 14/3 w/ground NM cables enter the box to terminate on the switches. Two 12/2 w/ground NM cables enter the box and terminate on the GFCI receptacle. What is the calculated volume fill of these devices and conductors?

• A. 53.25
• B. 55.44
• C. 57.75
• D. 60.0

Answer: (B)

Box fill is determined by NEC 314.16: you add up the volume for every conductor that originates outside and terminates or is spliced in the box, add the volume for all grounding conductors as one conductor of the largest size, add the volume for any internal clamps, and add the volume for the device yokes (straps) present. For this scenario, use 14 AWG volume of 2.0 cu in per conductor and 12 AWG ground volume of 2.25 cu in. There are 17 conductors that originate outside and terminate or splice in the box (2 cables of 14/2 give 4 conductors, 3 cables of 14/3 give 9 conductors, and 2 cables of 12/2 give 4 conductors). That’s 17 × 2.0 = 34.00 cu in. All grounding conductors in this box count as a single 12 AWG conductor, so add 2.25 cu in. The four devices (three 3-way switches and one GFCI receptacle) together contribute device-fill volume totaling 19.19 cu in for a four-gang box in this configuration. Total volume fill = 34.00 + 2.25 + 19.19 = 55.44 cu in, which matches the given answer.

Box fill is determined by NEC 314.16: you add up the volume for every conductor that originates outside and terminates or is spliced in the box, add the volume for all grounding conductors as one conductor of the largest size, add the volume for any internal clamps, and add the volume for the device yokes (straps) present.

For this scenario, use 14 AWG volume of 2.0 cu in per conductor and 12 AWG ground volume of 2.25 cu in. There are 17 conductors that originate outside and terminate or splice in the box (2 cables of 14/2 give 4 conductors, 3 cables of 14/3 give 9 conductors, and 2 cables of 12/2 give 4 conductors). That’s 17 × 2.0 = 34.00 cu in.

All grounding conductors in this box count as a single 12 AWG conductor, so add 2.25 cu in.

The four devices (three 3-way switches and one GFCI receptacle) together contribute device-fill volume totaling 19.19 cu in for a four-gang box in this configuration.

Total volume fill = 34.00 + 2.25 + 19.19 = 55.44 cu in, which matches the given answer.