Box Fill Calculation

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pcengineer

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Hello, I am look for some help regarding box fill calculations for a NEMA 14-50R receptacle. Since this is a larger device, I anticipate a double gang wall box will be necessary, but I am not sure how to calculate the volume. If someone can help break down the calculation assuming 4AWG and 6AWG wire, I would really appreciate it. Thanks in advance.
 
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wwhitney

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Dennis Alwon

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#6 wire is the equivalent of 5 cu. in so if you have 4 wire-- 3 wires are #6 and 1 is #10

3 x 5 = 15
1 x 2.5 (for #10) = 2.5
Now you have 4 conductors for the receptacle because it fits in 2 gang box.
4 x 5 = 20 cu. in
Assuming no clamps

20 +15 +2.5 = 37.5 cu.in
 
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Rick 0920

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pcengineer said:
Hello, I am look for some help regarding box fill calculations for a NEMA 14-50R receptacle. Since this is a larger device, I anticipate a double gang wall box will be necessary, but I am not sure how to calculate the volume. If someone can help break down the calculation assuming 4AWG and 6AWG wire, I would really appreciate it. Thanks in advance.
Click to expand...
You would need to count this device as 4 volume allowances. For example, if you installed a 6-3 w/ground for a 50A range circuit, the calculation would result as follows:
3 - allowances for insulated #6 conductors @ 5.00 cu. in. each = 15 cu. in.
1 - allowance for cable clamp (Carlon's website tells you that their cable openings are NOT factored in when figuring box fill) = 5.00 cu. in.
4 - allowances for the device @ 5.00 cu. in. each = 20. cu. in.
1 - allowance for a #10 EGC @ 2.5 cu. in. = 2.5 cu. in.

Minimum cu. in. box size - 42.5 cu. in.
 
Dennis Alwon

Dennis Alwon

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Rick 0920 said:
You would need to count this device as 4 volume allowances. For example, if you installed a 6-3 w/ground for a 50A range circuit, the calculation would result as follows:
3 - allowances for insulated #6 conductors @ 5.00 cu. in. each = 15 cu. in.
1 - allowance for cable clamp (Carlon's website tells you that their cable openings are NOT factored in when figuring box fill) = 5.00 cu. in.
4 - allowances for the device @ 5.00 cu. in. each = 20. cu. in.
1 - allowance for a #10 EGC @ 2.5 cu. in. = 2.5 cu. in.

Minimum cu. in. box size - 42.5 cu. in.
Click to expand...

Great-- I assumed, as stated, no clamp so now he can see both calculations. 👍
 
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pcengineer

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wwhitney said:
For #6 and smaller, the calculation is spelled out in NEC 314.16(B), see here:


Ampacity wise, #4 conductors would only be required if using Aluminum, for a 50A circuit, and a receptacle only rated for 60C conductors. So that scenario can be avoided by using a 60C/75C rated receptacle. Of course, on a long run conductors might require upsizing for voltage drop.

Cheers, Wayne
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Thank you for the response, Wayne! That link is very helpful and I will be adding it to my Bookmarks on my computer.
 
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pcengineer

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Dennis Alwon said:
#6 wire is the equivalent of 5 cu. in so if you have 4 wire-- 3 wires are #6 and 1 is #10

3 x 5 = 15
1 x 2.5 (for #10) = 2.5
Now you have 4 conductors for the receptacle because it fits in 2 gang box.
4 x 5 = 20 cu. in
Assuming no clamps

20 +15 +2.5 = 37.5 cu.in
Click to expand...
Thank you, Dennis! I appreciate you performing the calculation for my understanding. It was super helpful!
 
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pcengineer

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Location
New York
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Mechanical Engineer
Rick 0920 said:
You would need to count this device as 4 volume allowances. For example, if you installed a 6-3 w/ground for a 50A range circuit, the calculation would result as follows:
3 - allowances for insulated #6 conductors @ 5.00 cu. in. each = 15 cu. in.
1 - allowance for cable clamp (Carlon's website tells you that their cable openings are NOT factored in when figuring box fill) = 5.00 cu. in.
4 - allowances for the device @ 5.00 cu. in. each = 20. cu. in.
1 - allowance for a #10 EGC @ 2.5 cu. in. = 2.5 cu. in.

Minimum cu. in. box size - 42.5 cu. in.
Click to expand...
Rick, I appreciate you doing the calculation with the allowance for cable clamp. I have been seeing the cable clamp being accounted for sometimes and left out other times. Is there a reason why I should include it? Is it based on the wall box I am using? Thank you so much!
 
Dennis Alwon

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Here is the section on that clamp fill.


(2) Clamp Fill. Where one or more internal cable clamps,
whether factory or field supplied, are present in the box, a
single volume allowance in accordance with Table 314.16(B)
shall be made based on the largest conductor present in the
box. No allowance shall be required for a cable connector with
its clamping mechanism outside the box.
A clamp assembly that incorporates a cable termination for
the cable conductors shall be listed and marked for use with
specific nonmetallic boxes. Conductors that originate within
the clamp assembly shall be included in conductor fill calculations
covered in 314.16(B)(1) as though they entered from
outside the box. The clamp assembly shall not require a fill
allowance, but the volume of the portion of the assembly that
remains within the box after installation shall be excluded from
the box volume as marked in 314.16(A)(2).
Click to expand...
 
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wwhitney

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Dennis Alwon said:
Now you have 4 conductors for the receptacle because it fits in 2 gang box.
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Most NEMA 14-50 receptacles I've looked at say they require a 2 gang box, but here's the cut sheet for one that says "Flush-mount devices fit single or 2-Gang outlet boxes".


If we accept that it can be mounted in a single gang box, then it would only count as 2 allowances, I believe, even though it's wider than 2".

Cheers, Wayne
 
Dennis Alwon

Dennis Alwon

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wwhitney said:
Most NEMA 14-50 receptacles I've looked at say they require a 2 gang box, but here's the cut sheet for one that says "Flush-mount devices fit single or 2-Gang outlet boxes".


If we accept that it can be mounted in a single gang box, then it would only count as 2 allowances, I believe, even though it's wider than 2".

Cheers, Wayne
Click to expand...


I agree with #10 wire we used to install the dryer receptacles in a one gang box but he needs a 2 gang so imo, he needs to consider the receptacle as 4.
 
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wwhitney

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Dennis Alwon said:
I agree with #10 wire we used to install the dryer receptacles in a one gang box but he needs a 2 gang so imo, he needs to consider the receptacle as 4.
Click to expand...
The wording in (2017) 314.16(B)(4) is "A device or utilization equipment wider than a single 50 mm (2 in.) device box as described in Table 314.16(A) shall have double volume allowances provided for each gang required for mounting."

So if only one gang is required, then only one double allowance is necessary. That raises the question of what "required" means in this context. You might say that if a device fits in a single gang box, then only one gang is required.

On the other hand, the gang spacing on a multigang box is 1-13"/16" by my measurement. So if a 14-50 receptacle, even one mountable in a single gang box, would take up two spaces in a multigang box, then you could say that two gangs are required. This is a possibility as a single gang box is wider than 1-13/16" on the interior, just not wide enough for 2 gangs.

So I guess I'm back to agreeing that a 14-50 always requires 4 volume allowances, even when mountable in a single gang box.

Cheers, Wayne
 
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Rick 0920

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Electrical Instructor
pcengineer said:
Rick, I appreciate you doing the calculation with the allowance for cable clamp. I have been seeing the cable clamp being accounted for sometimes and left out other times. Is there a reason why I should include it? Is it based on the wall box I am using? Thank you so much!
Click to expand...
If you use a box that has them factory installed and you can't remove them, you have to count them. If you want to use a 2 gang nonmetallic box, Arlington makes one that has knockouts so you can use Romex connectors. If the clamping mechanism is outside of the box, there is no reduction needed for these type of clamps
 
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wwhitney

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Rick 0920 said:
(Carlon's website tells you that their cable openings are NOT factored in when figuring box fill)
Click to expand...
The only document I could find on Carlon's website is an FAQ from 20 years ago. Do you have a more recent reference?

I'm a bit doubtful of this interpretation. I means yes, when you use the cable clamp on a multi-gang Carlon box, the bendable tab does bend into the former volume of the box slightly. But the volume taken up is no more than the interior portion of a button connector or the locknut of a metal cable connector.

And the clamping action is between two parts of the plastic box, there no clamp protruding into the box. So I'd happily argue that the clamp is not internal to the box (unlike the metal NM clamps you can get in 4 square boxes, for example).

Cheers, Wayne
 
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