Carlon single gang box claims it holds 4 #12/2's AND a receptacle, but wait...

[poopypants]

Carlon B125AB
these boxes are pretty cool:
>single gang with steel stud mount or wood stud nails
>convertible from new construction to remodeler box
>internal provisions for drywall screw mounting - both vertically and horizontally
>best of all, the box nub is set to 1/2" unlike other carlon boxes that are set at 3/8"
>claims wire volume for 11 #12's. That's ground shattering for a single gang box i feel

Inside the box is stamped this:
24.5 cubic inches
12 #14
11 #12
10 #10

So my understanding of conduit wire fill and box wire fill is that the .8 remainder rule of rounding up doesn't apply to boxes, only conduits. Correct me if I'm wrong or something, but how can the manufacturer divide 2.25 (fill allowance for #12) into 24.5 (box cubic volume) and not get 10.8? Wouldn't you need to drop the .8 and be left with 10 #12's; not the manufacturer's claim of 11 #12's?

Looking at the 12 #14 shows that the remainder of .25 correctly got dropped. But looking at the 10 #10 shows the same .8 again got rounded up. Does anyone have insight to what is going on here?

 

[LarryFine]

I'm under the impression that manufacturers' markings trump code-based calculations, like with conduit bodies.

 

[kwired]

Many code calculations rounding is permitted unless a situation that says otherwise.

on the 14 AWG, 24.5 / 2 = 12.25. Rounding rules typically are less than .5 round down, .5 or more round up.

They rounded the 10 AWG figure up from 9.8 to 10 as well.

 

[480sparky]

I'm under the impression that manufacturers' markings trump code-based calculations, like with conduit bodies.

That would be correct.

 

[Greentagger]

Carlon B125AB
these boxes are pretty cool:
>single gang with steel stud mount or wood stud nails
>convertible from new construction to remodeler box
>internal provisions for drywall screw mounting - both vertically and horizontally
>best of all, the box nub is set to 1/2" unlike other carlon boxes that are set at 3/8"
>claims wire volume for 11 #12's. That's ground shattering for a single gang box i feel

Inside the box is stamped this:
24.5 cubic inches
12 #14
11 #12
10 #10

So my understanding of conduit wire fill and box wire fill is that the .8 remainder rule of rounding up doesn't apply to boxes, only conduits. Correct me if I'm wrong or something, but how can the manufacturer divide 2.25 (fill allowance for #12) into 24.5 (box cubic volume) and not get 10.8? Wouldn't you need to drop the .8 and be left with 10 #12's; not the manufacturer's claim of 11 #12's?

Looking at the 12 #14 shows that the remainder of .25 correctly got dropped. But looking at the 10 #10 shows the same .8 again got rounded up. Does anyone have insight to what is going on here?

what about allowance for the device?

 

[LarryFine]

what about allowance for the device?

That still counts as two of the size of conductors attached to it.

 

[Dennis Alwon]

I think if you take 11 (#12 conductors) and multiply by 2.25 you get 24.75

Box is 24.5 which is a difference of .25in so you don't need to worry about it...

 

[Jerramundi]

Generally speaking, volume is volume. You can't take a certain volume and fill it with something of a greater volume.
That just not how math works, lol.

That being said, the volumes that we utilize are NOT precise. If they were, the 2.25 volume for #12's as applied to a device wired to #12's would change between things like (1) a toggle switch and (2) a dimmer (i.e. the two devices are clearly of different "volumes" and yet get the same value when doing box fill calculations).

So box volume in the NEC isn't the same thing as the volume of a 16oz water bottle.

Either those that approved this item (1) didn't care about the rounding up or (2) didn't notice it.
Either way, I think @LarryFine has a point about manufacturers specs superseding the NEC.

Normally I'd share your curiosity and rant and rave until it made sense, but I'm tired, lol.

 

[Little Bill]

Generally speaking, volume is volume. You can't take a certain volume and fill it with something of a greater volume.
That just not how math works, lol.

That being said, the volumes that we utilize are NOT precise. If they were, the 2.25 volume for #12's as applied to a device wired to #12's would change between things like (1) a toggle switch and (2) a dimmer (i.e. the two devices are clearly of different "volumes" and yet get the same value when doing box fill calculations).

So box volume in the NEC isn't the same thing as the volume of a 16oz water bottle.

Either those that approved this item (1) didn't care about the rounding up or (2) didn't notice it.
Either way, I think @LarryFine has a point about manufacturers specs superseding the NEC.

Normally I'd share your curiosity and rant and rave until it made sense, but I'm tired, lol.

No one is asking about "precise measurements". We have to go by the mfg stamped volume or box size chart in the code book, then by the volume listed for each wire size.

 

[James L]

That's an awful lot of conductors in a single gang.
I know the math works, but trying to pigtail that for a receptacle could be rough.

Kinda curious about the dimensions, too.

I use Allied Moulded fiberglass boxes. The 1099 is 22.5 cu.in. and dang near the whole depth of a 2x4 stud. Wondering where Carlon found an extra 2 cu.in.

 

[AC\DC]

https://rexel-cdn.com/Products/AlliedMoulded/P-241QT.pdf?i=B24CAAEA-A8D2-4517-B1D2-FBA684237154

https://rexel-cdn.com/Products/AlliedMoulded/SB-1.pdf?i=73C9BB20-ACC9-4D31-BC5E-D1B73EE9B7BD

Switch to these and you can get a couple more Cu.in

I use Allied Moulded fiberglass boxes. The 1099 is 22.5 cu.in. and dang near the whole depth of a 2x4 stud. Wondering where Carlon found an extra 2 cu.in.

Would like a single gang at 26 or 28 cu.in have not found any

 

[James L]

https://rexel-cdn.com/Products/AlliedMoulded/P-241QT.pdf?i=B24CAAEA-A8D2-4517-B1D2-FBA684237154

https://rexel-cdn.com/Products/AlliedMoulded/SB-1.pdf?i=73C9BB20-ACC9-4D31-BC5E-D1B73EE9B7BD

Switch to these and you can get a couple more Cu.in

Would like a single gang at 26 or 28 cu.in have not found any

2-1/8" deep 1900 box with single gang mud ring gets you almost 40 cu.in.

 

[AC\DC]

Plastic, I should of specified.

 

[wwhitney]

Plastic, I should of specified.

You can get the same combination in plastic:

Carlon A5217DE 4" x 4" x 2-3/8" box
Carlon A410 through A414 single gang mudrings

Cheers, Wayne

 

[AC\DC]

forgot about those, lol only used the metal version. Thanks

 

[Dennis Alwon]

I don't believe this is about manufacturer spec superceding the NEC. I feel confident that the NEC allows this based on post 7 calculation

 

[Jerramundi]

No one is asking about "precise measurements"...

I disagree. In asking about how this is allowable in that it conflicts with the code, the OP IS indeed asking about the nature of precise measurements in regards to box fill calculations.

We have to go by the mfg stamped volume or box size chart in the code book, then by the volume listed for each wire size.

I am not in disagreement that this is the accepted, code-approved procedure.
I'm simply pointing out that box fill is not an exact science, thus lending to the idea that the conflict between what the manufacturer states in this instance and the code approved methodology is not much to be concerned about.

 

[Jerramundi]

I don't believe this is about manufacturer spec superceding the NEC. I feel confident that the NEC allows this based on post 7 calculation

It must be about this because the post #7 calculation would be negated by the NEC.
There's nothing in the NEC that says "look the other way regarding 0.25 cu in of box fill."

The only explanation is that manufacturer's spec supersede the NEC, otherwise we are forced to conclude that allowable number of conductors as stated by the manufacturer here is a code violation.

 

[wwhitney]

90.1(A) Practical Safeguarding . . . it's not practical to sweat 0.25 in³? : - )

Cheers, Wayne

 

[Jerramundi]

Now that I think about it (and correct me if I'm wrong)...

There's NOTHING in the NEC that allows us to go by the # OF CONDUCTORS as allowed by the manufacturer.
The NEC ONLY allows to us utilize the VOLUME as stated by the manufacturer.

If true, we should ignore any number of conductors allowed as stated by the manufacturer and ONLY utilize the box volume they provide in doing our own calculations.