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I have a single gang box that measures 3x2.5x2" which gives a volume of 15 cubic inches.

The volume required for 14 AWG conductor is 2 cubic inches. If I have a simple case of 14/2 going in and 14/2 going out, with 1 switch and 1 clamps, I get a volume of 16 cubic inches:

4 conductors = 8 cubic inches
1 clamps = 2 cubic inches
1 device = 4 cubic inches
1 ground = 2 cubic inches

These 15 cubic inch boxes are pretty common but it seems you can only get one 14/2 wire into this box. What do electricians do when they need to have one 14/2 wire in and one 14/2 or even two 14/2 out on a single gang? What happens if you need to bump up the gauge to 12/2 or you have a 3-way switch and need to use a 14/3 wire with a 14/2?

Thanks.
 

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I have a single gang box that measures 3x2.5x2" which gives a volume of 15 cubic inches.

The volume required for 14 AWG conductor is 2 cubic inches. If I have a simple case of 14/2 going in and 14/2 going out, with 1 switch and 1 clamps, I get a volume of 16 cubic inches:

4 conductors = 8 cubic inches
1 clamps = 2 cubic inches
1 device = 4 cubic inches
1 ground = 2 cubic inches

These 15 cubic inch boxes are pretty common but it seems you can only get one 14/2 wire into this box. What do electricians do when they need to have one 14/2 wire in and one 14/2 or even two 14/2 out on a single gang? What happens if you need to bump up the gauge to 12/2 or you have a 3-way switch and need to use a 14/3 wire with a 14/2?

Thanks.

You need a 2 3/4" deep box to use two 14/2 Romex cables. Many codes ago the devices were not counted for box fill and a 2.5" gem box was fine for a cable in/cable out wiring scheme.

If you can only use a 2.5" box, then get one with 1/2" knockouts and use a Romex connector. They do not take up any box fill.
 

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Are you measuring the box and calculating the size? You should use the size printed on the box.

BTW, that hub/spoke wiring you mentioned is the worst wiring method. More splices in places you don't want to be working.
 
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Would the other scheme be something like hub and spoke? For example, a junction box in say the crawlspace with one in and say 5 out?

Thanks everyone for quick responses!
I agree with RJ. Avoid junction boxes in far off places if you can. Is there some reason why you can't use bigger outlet boxes? Or do you have a bunch of 2.5" gem boxes that you want to get rid of?
 

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Discussion Starter · #8 ·
I agree with RJ. Avoid junction boxes in far off places if you can. Is there some reason why you can't use bigger outlet boxes? Or do you have a bunch of 2.5" gem boxes that you want to get rid of?
I purchased new boxes - 18.5 cu for single gang and 15 cu for gangable boxes.

I am using 12 AWG. Say I have a 3-way light switch. So 2 conductors in and 3 conductors out. And additional 2 conductors out to power the next unrelated switch. When I do the math, the 18.5 cu box is not big enough for 2 clamps, 1 device, 1 ground and 7 conductors.
 

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I purchased new boxes - 18.5 cu for single gang and 15 cu for gangable boxes.

I am using 12 AWG. Say I have a 3-way light switch. So 2 conductors in and 3 conductors out. And additional 2 conductors out to power the next unrelated switch. When I do the math, the 18.5 cu box is not big enough for 2 clamps, 1 device, 1 ground and 7 conductors.
Use 4" square boxes with mud rings or 3.5" gem boxes.
 

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I purchased new boxes - 18.5 cu for single gang and 15 cu for gangable boxes.

I am using 12 AWG. Say I have a 3-way light switch. So 2 conductors in and 3 conductors out. And additional 2 conductors out to power the next unrelated switch. When I do the math, the 18.5 cu box is not big enough for 2 clamps, 1 device, 1 ground and 7 conductors.
Correct, the box is still too small. The clamps count as one volume. a device counts as two volumes.
 

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Your figures are incorrect unless BC uses different number than Ontario.
Clamps don't count but wire nuts do If you have two or more.
Grounds don't count.

#14 = 1.5 ci
#12 = 1.75 ci

My count
4 conductors - 6 ci
1 switch - 3 ci.
Guess one wire nut for neutral = 0 count.
0 count for ground.

You need a 9 ci box.

According to table 23 a 3x2x2.5 box can take 8 #14 conductors. Your count is only at 6. You are fine.
 
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