Box Fill Calculation Question

[69_sportsroof]

Hello all, I'm wiring up my garage, and reading the code, I thought I was fine, but now I'm wondering if I should've ordered extra deep boxes(none were in stock at either of my local home improvement stores so it struck me as not common to use and my setup doesn't seem farfetched). I have two duplex receptacles on two different phases.

Florida code says this:
E3905.12.2 Box fill calculations.
The volumes in Section E3905.12.2.1 through Section E3905.12.2.5, as applicable, shall be added together. No allowance shall be required for small fittings such as locknuts and bushings.

E3905.12.2.1 Conductor fill.
Each conductor that originates outside the box and terminates or is spliced within the box shall be counted once, and each conductor that passes through the box without splice or termination shall be counted once. Each loop or coil of unbroken conductor having a length equal to or greater than twice that required for free conductors by Section E3406.10.3, shall be counted twice. The conductor fill, in cubic inches, shall be computed using Table E3905.12.2.1. A conductor, no part of which leaves the box, shall not be counted.

E3905.12.2.4 Device or equipment fill.
For each yoke or strap containing one or more devices or equipment, a double volume allowance in accordance with Table E3905.12.2.1 shall be made for each yoke or strap based on the largest conductor connected to a device(s) or equipment supported by that yoke or strap. For a device or utilization equipment that is wider than a single 2-inch (51 mm) device box as described in Table E3905.12.1, a double volume allowance shall be made for each ganged portion required for mounting of the device or equipment.

I have two setups I'm worried about, In one case I have two leviton slim GFCIs in a box, with 2 12awg hots and 2 12awg neutrals, one ground coming into the box. One phase goes to each GFCI, then leaves the box. Code says a 12AWG conductor needs 2.25 cubic inches. My interpretation is 4 wires originate outside the box, and then each GFCI needs 2.25*2=4.5 c.i., total of 9 c.i. for GFCIs, plus the 4 conductors need another 9 c.i., so I'm at 18, which is under the 21c.i. of my box.

The other case is my junction boxes, I have the two phases two hots, two neutrals, and a ground coming in, splicing down to receptacles in another box, and then continuing on to the next box. So 45 wires in, spliced two ways out. The way I read the code, only 45 wires originate outside the box so I have 911.25 c.i. of fill, the rest originate inside the box, so my volume should be okay?

All my boxes are 4"x4"x1.5" and I've already mounted them and pulled wire so I'm really hoping I didn't mess this up. Any input?

edit: Counting all 3 sets of 5 wires in the junction box gives me a volume of 33.75 c.i.(15*2.25), and I only see boxes up to 30.3 cubic inches, so I feel like that's an invalid method as well.

 

[Stuff]

You forgot to include the ground in the calcs so might need a bigger box for the first one. Metal or plastic boxes?

I don't understand your description about phases. Normally we refer to cables and wires in those cables. A conductor is an individual wire.

 

[69_sportsroof]

I left out some context. These are all metal boxes, I am running individual THHN wires inside of EMT, it's a steel garage building with exposed metal studs/no drywall.

Somewhere I read grounds don't count towards conductor fill, but I can't remember where so it may be incorrect. If it does I'm under the volume by 0.75 c.i. still(2.25 c.i per 12awg wire) for the GFCI boxes.

Sorry, I believe poles is the term where I used phases. I have black, white, red, white, green wires coming into the junction boxes. The black and red are fed by the two separate poles in the subpanel.

 

[Stuff]

Ground wires are optional for metal boxes with EMT so that might have led to the confusion.

Something's not right with your calcs. The wording is terrible as "Originate outside the box" normally means all wires coming into the box. It doesn't care about the source of power.

Your first box has 1 red, 1 black, 2 whites and a green coming in but you said "leaves the box." So you have 1 red, 1 black, 2 whites, and a green going out? If so, that would count as 9 conductors.

Your second box would have 5 wires in each EMT pipe? Ground only counts once so your total would be 3*4+1=13 conductors.

 

[69_sportsroof]

I found an article that went into explanation, you're correct, originate does not mean power source as I thought.

The two gfci case is being fed two poles by the subpanel, and then the load terminals will feed/protect receptacles down the line. Coming in is black, red, white, white, green. Going out is black, red, white, white, green. Then each gfci is 2 conductors, so 13 conductors.

I swung by the store on the way home and bought some 1.5" extension rings for the junction boxes and a 30.3 c.i. box for the gfcis. Easy enough fix

Sent from my XT1575 using Tapatalk

 

[Orionrising]

Your first box has 1 red, 2 black, 2 whites and a green coming in but you said "leaves the box." So you have 1 red, 2 black, 2 whites, and a green going out? If so, that would count as 9 conductors.

This part confuses me. Why are they counted twice? Isn't that a splice and then counted once since it's the same conductor? Each end of a splice is counted separate?


Sent from my Moto G (4) using Tapatalk

 

[Orionrising]

Bleh apparently yes... I will need box extensions to keep fill happy for expansion...

Sent from my Moto G (4) using Tapatalk

 

[CJ7VFR]

This part confuses me. Why are they counted twice? Isn't that a splice and then counted once since it's the same conductor? Each end of a splice is counted separate?


Sent from my Moto G (4) using Tapatalk

Yes, as you found out, each end is counted separate. It doesn't matter if it is a splice to continue the same circuit, or if you have multiple circuits run to the same box. They count each conductor that is entering the box. Except for ground wires for some reason. They count all the grounds in a box as just one I do believe. And pigtails inside the box usually don't add to the count which is odd, since they also take up space.

And you also have to figure the size of the conductor also. Heavier gauge wire can count for more. 14 gauge is considered 2.00 cubic inches and 12 gauge wire is considered 2.25 cubic inches as others have posted.

Also, don't forget to figure in the space taken up by switches and receptacles if you are going to use any.

Jim

 

[CJ7VFR]

Your first box has 1 red, 2 black, 2 whites and a green coming in but you said "leaves the box." So you have 1 red, 2 black, 2 whites, and a green going out? If so, that would count as 9 conductors...

Wouldn't this count as 11 conductors all together? 2 red, 4 black, 4 white, and one for ground?

Jim

 

[grounded-b]

Hello all, I'm wiring up my garage, and reading the code, I thought I was fine, but now I'm wondering if I should've ordered extra deep boxes(none were in stock at either of my local home improvement stores so it struck me as not common to use and my setup doesn't seem farfetched). I have two duplex receptacles on two different phases.

Florida code says this:
E3905.12.2 Box fill calculations.
The volumes in Section E3905.12.2.1 through Section E3905.12.2.5, as applicable, shall be added together. No allowance shall be required for small fittings such as locknuts and bushings.

E3905.12.2.1 Conductor fill.
Each conductor that originates outside the box and terminates or is spliced within the box shall be counted once, and each conductor that passes through the box without splice or termination shall be counted once. Each loop or coil of unbroken conductor having a length equal to or greater than twice that required for free conductors by Section E3406.10.3, shall be counted twice. The conductor fill, in cubic inches, shall be computed using Table E3905.12.2.1. A conductor, no part of which leaves the box, shall not be counted.

E3905.12.2.4 Device or equipment fill.
For each yoke or strap containing one or more devices or equipment, a double volume allowance in accordance with Table E3905.12.2.1 shall be made for each yoke or strap based on the largest conductor connected to a device(s) or equipment supported by that yoke or strap. For a device or utilization equipment that is wider than a single 2-inch (51 mm) device box as described in Table E3905.12.1, a double volume allowance shall be made for each ganged portion required for mounting of the device or equipment.

I have two setups I'm worried about, In one case I have two leviton slim GFCIs in a box, with 2 12awg hots and 2 12awg neutrals, one ground coming into the box. One phase goes to each GFCI, then leaves the box. Code says a 12AWG conductor needs 2.25 cubic inches. My interpretation is 4 wires originate outside the box, and then each GFCI needs 2.25*2=4.5 c.i., total of 9 c.i. for GFCIs, plus the 4 conductors need another 9 c.i., so I'm at 18, which is under the 21c.i. of my box.

The other case is my junction boxes, I have the two phases two hots, two neutrals, and a ground coming in, splicing down to receptacles in another box, and then continuing on to the next box. So 45 wires in, spliced two ways out. The way I read the code, only 45 wires originate outside the box so I have 911.25 c.i. of fill, the rest originate inside the box, so my volume should be okay?

All my boxes are 4"x4"x1.5" and I've already mounted them and pulled wire so I'm really hoping I didn't mess this up. Any input?

edit: Counting all 3 sets of 5 wires in the junction box gives me a volume of 33.75 c.i.(15*2.25), and I only see boxes up to 30.3 cubic inches, so I feel like that's an invalid method as well.

In your second example - Yes, you need to count ALL the wires entering and leaving the box. For a total of 13. Remember, you only count the ground ONCE. So you get a total of 13 x 2.25 = 29.25 cu in

You're OK with a 4 sqr , 1 1/2" deep box. Plus, your are allowed to add the cu. inch volume of the raised cover you are installing

 

[Stuff]

Wouldn't this count as 11 conductors all together? 2 red, 4 black, 4 white, and one for ground?

Jim

I believe that I counted right but you are right in that I identified the wires wrong. Should have said 1 red, 1 black, 2 white and ground in and out. So total of 2 red, 2 black, 4 white and grounds = 9

 

[Stuff]

In your second example - Yes, you need to count ALL the wires entering and leaving the box. For a total of 13. Remember, you only count the ground ONCE. So you get a total of 13 x 2.25 = 29.25 cu in

You're OK with a 4 sqr , 1 1/2" deep box. Plus, your are allowed to add the cu. inch volume of the raised cover you are installing

Tables show 4 square 1 1/2" box is rated at 21 square inches. So even with a raised cover it would not be big enough.

 

[mm08822]

Per NEC:
Each current carrying conductor entering the box is counted. Whether its power in/power out doesn’t matter.
Unspliced wires passing thru the box only count as one
All grounds count as 1 total (if you didn’t pull a grd wire then it is 0)
Each yoke counts as 2
Wires originating and terminating in the box don’t add into the count
Since you have conduit there are no internal clamps to consider
Fixture studs would also count, but not for your application
Typical 4” sq raised cover provides 6.5 cu. in.

Seems like 4”sq x 2-1/8” deep are a better choice for your initial needs and allowance for future.
This box would give you 15 #14’s or 13 #12’s plus 2-3 from raised cover. (18 equivalent #14’s or 15 #12’s).

You can even use 4-11/16" sq x 1-1/2 or 2-1/8" deep if your conduit/circuit routing requires even more box fill. These would be used sparingly, not throughout the entire job. They make device covers for them too.

 

[grounded-b]

Yup. you're right. I saw the OP mention 31 in cu., but that was for a 2 1/8" deep box

 

[CJ7VFR]

I believe that I counted right but you are right in that I identified the wires wrong. Should have said 1 red, 1 black, 2 white and ground in and out. So total of 2 red, 2 black, 4 white and grounds = 9

That sounds good to me. I thought maybe I was missing something!

Jim

 

[matt_i]

Jmo, but anything EMT/PVC + metal boxes is ripe for expansion since all the hard work has already been done, and its usually very easy to fish new circuits. Along those lines I always default to the deeper box, its just easier to work with in any case.