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

[kwired]

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.

Now you are getting into having higher pressure or density in the same amount of volume - time to go with compact conductors I guess

 

[Jerramundi]

The UL standard requires the volume to be marked on the inside of the box and the code requires that you use that volume for the wire fill calculations.

Agreed. I think this is the correct interpretation. In other words, using the number of conductors stamped on the box is not the code approved procedure. You can and should use the volume that's stamped there, but the conductor fill needs to be done per code.

 

[kwired]

Box fill is a little bit of a joke to begin with. Some boxes that are in compliance with the rules are much more crowded than some that are overfilled according to the rules. Take a 4x4 box with fairly full raceway (even just half inch raceway) with all conductors pulled straight through with no loops other than what is needed to connect to one device in said box. Many times that will be overfilled in accordance to the rules. Then take similar box with splices in all conductors, keeping number of conductors below max fill and though that box is not overfilled is much more crowded

 

[Jerramundi]

Box fill is a little bit of a joke to begin with. Some boxes that are in compliance with the rules are much more crowded than some that are overfilled according to the rules. Take a 4x4 box with fairly full raceway (even just half inch raceway) with all conductors pulled straight through with no loops other than what is needed to connect to one device in said box. Many times that will be overfilled in accordance to the rules. Then take similar box with splices in all conductors, keeping number of conductors below max fill and though that box is not overfilled is much more crowded

How is a 4 x 4 box "...with all conductors pulled straight through with no loops other than what is needed to connect to one device... overfilled in accordance to the rules" ??

Even with #10's, on a device taking 3 wires, you're looking at max 12.5 cu, which is only a few cu over half of your standard 1900 (not including the additional volume provided by the mudring, which would likely make it about 1/2" of the allotted fill).

 

[LarryFine]

Heat contribution may have as much to do with it as heat dissipation. And perhaps insulation damage.

 

[kwired]

How is a 4 x 4 box "...with all conductors pulled straight through with no loops other than what is needed to connect to one device... overfilled in accordance to the rules" ??

Even with #10's, on a device taking 3 wires, you're looking at max 12.5 cu, which is only a few cu over half of your standard 1900 (not including the additional volume provided by the mudring, which would likely make it about 1/2" of the allotted fill).

Ok, 1/2" raceway might be little tougher to overfill, pretty sure I've had many cases with 3/4" that have too much box fill taken up yet there is a lot of room with bulk of what is in there passing straight through.

With 3/4" you can have some 6 AWG conductors in there in some cases where 1/2" you won't and if you had 8 AWG in a 1/2 inch chances are it is only a single circuit in the run