Larry Bohn
Member
- Location
- ashland, oregon
Box fill is easy, right?
If I have a box with a duplex receptacle, two #14 wires landing on the receptacle, a #14 ground and a cable clamp, the total inches required is 12 cubic inches. Now I want to add to the calculation nine #10 THHN conductors passing through the box, no loop. These conductors are in a 3/4" EMT secured to the box by lock rings. The #10 conductors add an additional 2.5" X 9 = 22.5". Is the clamp size increased from 2 to 2.5? If so, the total cubic inches added to the first calculation is 23 cubic inches, now the total is 35.
Now the question is a bit harder. Suppose three of the #10 are green. Now we have four grounding wires "entering" the box, three of which pass straight through, making four green wires. Only one green, the largest, is required to be counted until the number of grounding conductors exceeds four. That leaves a clamp at 2.5, a receptacle at 4, two #14 wires at 4, one green at 2.5, six #10 passing through at 15. Total is now 28. the only difference between the 35 cubic inch calculation above and the 28 inches here is that I've said three of the wires are green.
Or do you still say nine conductors are still passing through and you'll add another half inch to the grounding wire size, making the calculation 35.5 inches. Now you have four grounding conductors entering a box and are you not counting all of them as grounding conductors.
The smart thing to do is cut, splice, pigtail and land all the green #10 wires in the box, that ends all confusion. Now the calculation comes out less than 30 cubic inches, over five inches less than if they pass through and I'll bet that box size doesn't work as well as you might hope
Or does the code intend, when it says "present in the box" or "entering the box" to really mean "utilized in the box" and passing through is just "passing through"?
If I have a box with a duplex receptacle, two #14 wires landing on the receptacle, a #14 ground and a cable clamp, the total inches required is 12 cubic inches. Now I want to add to the calculation nine #10 THHN conductors passing through the box, no loop. These conductors are in a 3/4" EMT secured to the box by lock rings. The #10 conductors add an additional 2.5" X 9 = 22.5". Is the clamp size increased from 2 to 2.5? If so, the total cubic inches added to the first calculation is 23 cubic inches, now the total is 35.
Now the question is a bit harder. Suppose three of the #10 are green. Now we have four grounding wires "entering" the box, three of which pass straight through, making four green wires. Only one green, the largest, is required to be counted until the number of grounding conductors exceeds four. That leaves a clamp at 2.5, a receptacle at 4, two #14 wires at 4, one green at 2.5, six #10 passing through at 15. Total is now 28. the only difference between the 35 cubic inch calculation above and the 28 inches here is that I've said three of the wires are green.
Or do you still say nine conductors are still passing through and you'll add another half inch to the grounding wire size, making the calculation 35.5 inches. Now you have four grounding conductors entering a box and are you not counting all of them as grounding conductors.
The smart thing to do is cut, splice, pigtail and land all the green #10 wires in the box, that ends all confusion. Now the calculation comes out less than 30 cubic inches, over five inches less than if they pass through and I'll bet that box size doesn't work as well as you might hope
Or does the code intend, when it says "present in the box" or "entering the box" to really mean "utilized in the box" and passing through is just "passing through"?
JMO.
