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# Box fill question

#1
09-10-09, 06:21 AM
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Join Date: Sep 2005
Location: Just outside of Phila
Posts: 350
Box fill question

I have a 21 cubic inch box that has 3 12/2 ga cables in it. The cables are wire nutted together with a pigtail to a receptacle. Do the pigtails need to be added as part of the total volume? If so is my math correct? With the pigtails = 21.25 cubic inch Without the pigtails = 14.5 cubic inch Will I need a new box or am I ok? Thanks, John

#2
09-10-09, 07:03 AM
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Join Date: Feb 2005
Location: Near Lansing, Michigan
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Pigtails don't count in box fill. The fill should be:

Count the fill units: 6 conductors + 1 grounds + 2 receptacle = 9 fill units

Multiply by 2.25 cu in for #12 wire: 9 * 2.25 = 20.25

The minimum box size is 20.25 cubic inches.

#3
09-10-09, 07:22 AM
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Join Date: Sep 2005
Location: Just outside of Phila
Posts: 350
ibpooks, thanks for the reply. I just learned something new. I understand the 6 conductors and adding 1 for all the grounds but I wasn't sure about the pigtails. I also didn't realize that you had to add the recep to the fill count. So I'm assuming that if it were a simplex recep that the fill count would be 8, correct? And if it were a light switch it would also count as 1? I have the 2005 NEC but couldn't find that info anywhere.

Thank you
John

#4
09-10-09, 07:40 AM
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Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Any device (GFCI, receptacle, switch, etc) counts as 2 units. NEC Article 314.16 covers box fill; there are several sub sections which list the details of the calculation.

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