Confused about box fill

[exranger06]

Do box fill limitations only come into play when you have splices/junctions? If you have a box where a bunch of wires pass straight through with no splices, does the cu in capacity of the box matter?

I was under the impression that it always matters, even when there are no splices in the box. But I noticed something that has me confused.

I'm in the middle of a project- installing a new receptacle on a dedicated circuit in my finished basement. I'm using Wiremold 700 series. I was planning on using a 5719WH box in the corner of the room.

On the other side of the wall is an unfinished room, where I already have NM-b for this circuit installed. I was going to install a cable clamp on one of the knockouts and run the NM-b into this box, and splice it to THWN to run through the Wiremold. Then I realized that I can't splice it here due to box fill. This box is stamped as 10.3 cu in. I'm using 12 gauge wire, splicing a hot leg, neutral, and ground - 5 conductors total = 11.25 cu in. No good. So, I can either use a different Wiremold box, or use the knockout to install a conduit connector and run a short stub of conduit into the unfinished room and install a junction box there to transition to NM-b.

But looking at Wiremold's spec sheets, the 700 series raceway can hold seven 12 gauge conductors: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwjts-DJ5r7jAhWyzlkKHbQmBC4QFjAAegQIABAC&url=https%3A%2F%2Fwww.legrand.us%2F-%2Fmedia%2Fproducts%2Fresources%2Fwiremold-products%2Fraceway%2Fed342r11pdf.ashx&usg=AOvVaw0hCqR_BBV61nwHCnClnxqt
How is it that the conduit can carry 7 conductors, but this particular box, which is bigger than the conduit itself, can't even hold 5? Does the 10.3 cu in stamping on it only apply if I'm splicing wires in it, and not if the wires run straight through?

 

[TRWham]

Because the standards for raceways and j-boxes are different. I imagine the way UL makes Legrand measure the box limits the cubic capacity. If you turn the corner with an inside ell then run into a box with sufficient capacity, you can achieve nearly the same thing except the box will be slightly off the corner.

 

[exranger06]

Because the standards for raceways and j-boxes are different. I imagine the way UL makes Legrand measure the box limits the cubic capacity. If you turn the corner with an inside ell then run into a box with sufficient capacity, you can achieve nearly the same thing except the box will be slightly off the corner.

That was my original plan. Then I found this corner box and decided it is a much better looking and elegant way to install it. I think I'll stub conduit through the wall and stick a junction box there. I need a junction box there anyway, since my NM-b cable came up about 2 feet too short.

 

[RegeSullivan]

Conductors that pass thru count as 1, all grounds count as one.

Sent from my SM-N950U using The Garage Journal mobile app

 

[exranger06]

Conductors that pass thru count as 1, all grounds count as one.

Sent from my SM-N950U using The Garage Journal mobile app

Yes, I know that. I don't see what that has to do with my question.

 

[Bert_]

There are handy boxes with 3/4 knock outs. You will run out of box fill before conduit fill just like with this wiremold fitting. Just have to use whatever parts the situation requires.

My preference would be to eliminate the unnecessary splices and sleeve the Romex to the first outlet. Run thhn to any other outlets down the line.

 

[exranger06]

The Romex in the unfinished room is already installed and it's already 2 ft too short to go through the wall. I thought a 25 ft roll would be enough, but apparently not. So I need a junction box in that room regardless. I might as well transition to THWN in conduit there and connect the conduit to the Wiremold box. The wire will go right through the corner box with no splices through the whole length of Wiremold. There's only one receptacle for this whole circuit. I'm putting the "through-the-wall" window unit air conditioner on its own dedicated 20 amp circuit, as required by code. That way I won't have to use an extension cord every time I want to use it, like I do now.