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Old 06-01-2012, 08:41 AM   #1
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Total conducters allowed in a device box


I am trying to find out the max number of conductors allowed for a device box in CANADA. I suspect it may be different for the U.S.

My understanding is as follows:

1 #14/2 = 2 conductors
1 #14/3 = 3 conductors
all ground wires in a box = 1 conductor
1 a switch or 1 receptacle = 2 conductors (I believe this is the same for a 3 way switch)
each pair of marretts(2) = 1 conductor
all internal clamps whether used or not = 1 conductor

each conductor requires 1.5 cu inch for # 14 wire.

I expect that the volume required would be different for say #12 wire?

Now for an example:
a device box with 2 #14/2 and 1 #14/3 wires entering the device box.
The box contains 1 switch.
2 marretts are used inside the box

therefore:

2 #14/2 wire = 4 conductors
1 #14/3 wire = 3 conductores
1 switch = 2 conductors
2 marretts = 1 conductor
all grounds = 1 conductor
all clamps for the box whether used or not = 1 conductor
for a total of 12 conductors

12 conductors x 1.5 cu inch = 18.0 cu inch

I would need a box with a minimum volume of 18 cu inches

Am I understanding this correctly?

I would greatly appreciate any info on this topic.

Thanks

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Old 06-01-2012, 09:03 AM   #2
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Total conducters allowed in a device box


Here is a good note on this:

http://ecmweb.com/nec/code-basics/el..._calculations/

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Old 06-01-2012, 09:20 AM   #3
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Total conducters allowed in a device box


Thank you.

I had seen this earlier. I suspect this is the code for the U.S. I was wondering if it would be any different for Canada. Most of what I described in my post agrees with link you provided other than the cubic inch required for a conductor. I was under the impression the it was 1.5 cu inch in Canada. I certainly could be wrong.

Again thank you.

If anyone has info as far as the Canadian code is concerned, I would appreciate hearing from you.
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Old 06-01-2012, 12:00 PM   #4
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Total conducters allowed in a device box


Your count is 2 conductors too high.

Looking at my code book I see no mention of counting grounds. Grounds are not conductors. Only conductors are counted.

The rule 12-3034(5) actually states that "...'shall disregard any space occupied by lock nuts, bushings, box connectors or clamps".

Canadian code is also metric. #14 counts as 24.6ml which is 1.5 cubic inch.
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Old 06-01-2012, 03:17 PM   #5
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Total conducters allowed in a device box


Thanks for the info!

Your understanding is that grounds are not counted and the clamps in the device box are not counted which reduced my count by 2.

Not counting the grounds make sense - it was suggested to me that if all the grounds are tied with one marrett then that marrette is to be included with the marrette count (2 marretts - 1 conductor).

As far as the the clamps in the device I find some saying count it and others not to count it.

My father in law was an electrician all his life but has been retired for 15+ years and his comment was that codes change all the time (as well as memory) so he wasn't sure how it was calculated anymore. He didn't even have any old code books to look at.

I guess it doesn't hurt to go with bigger boxes if there is room to give one a warm fuzzy feeling that there is plenty of room.

I did realize that it was metric in Canada, but I guess I am a bit old school when it gets down to millimeters!!

Another question if I may - I would imagine that if #12 or #10 was used (don't think I will be - just curious) that it would require more than 1.5 cu inches for each conductor???

Thanks again for your help.
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Old 06-01-2012, 08:32 PM   #6
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Total conducters allowed in a device box


Under the NEC a #14 is 2 cubic inches, a #12 2.25 and a #10 is 2.5 cubic inches. I am sure the CEC also increases with the wire sizes.
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Old 06-01-2012, 09:02 PM   #7
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Total conducters allowed in a device box


I was reminded of this earlier today in another forum; Contact your local code authority, they are there to help. If your province is like my state, and allows homeowner’s to do their own electrical work, you may still be required to get a permit. A second set of eyes sometimes helps, also if there is a catastrophe and they find un-permitted work, insurance companies can deny claims, even if the actual cause was unrelated.
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Old 06-02-2012, 09:03 AM   #8
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Total conducters allowed in a device box


The marrette for the grounds would count but not the grounds themselves.
Larger wires would count for larger box fill. I don't have the numbers here.

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