Junction box sanity check

[Don1357]

This weekend I'm running two wires to the upstairs of the garage, one for lights, one for outlets. The lights will be on 14 to supply the 3 or so amps for the 40 Watt LED 4' lights will draw. The outlets are 12 wire for 15 amp outlets.

The plan is to run the two wires to a 4" junction box from where the wire for the light is just spliced out, the one for the outlets is spliced into two branches to go left and right. According to what I could research the box is big enough for this? And that there are no problems having the two different wires, which I plan on clearly labeling?

Bonus question: Is it ok to just tie the ground wires together or do they need to keep separate grounds? The plan is to keep them separated but I'm just curious if it is kosher to just merge them.

 

[exranger06]

It is impossible to say if the box is big enough or not without knowing the actual volume of it. 4" square boxes are available in many different depths, and therefore many different volumes. Each #14 wire takes 2 cubic inches of volume and each #12 wire takes 2.25 cu in of volume. All of the ground wires count as just one wire, so just add up the volume of all of the hot legs and neutrals, and add another 2.25 for all of the grounds (since #12 is the biggest ground wire, you use the volume of a #12 wire). You just need to make sure the total volume of all conductors doesn't exceed the volume of the box.

Yes, it is perfectly fine to have two different circuits and/or two different gauge wires in the same box.

Code actually REQUIRES you to tie all ground wires together, even when they're on different circuits. And if this is a metal box, don't forget to install a #12 bonding jumper to the box and tie that in to all of the ground wires.

 

[Don1357]

It is impossible to say if the box is big enough or not without knowing the actual volume of it. 4" square boxes are available in many different depths, and therefore many different volumes. Each #14 wire takes 2 cubic inches of volume and each #12 wire takes 2.25 cu in of volume. All of the ground wires count as just one wire, so just add up the volume of all of the hot legs and neutrals, and add another 2.25 for all of the grounds (since #12 is the biggest ground wire, you use the volume of a #12 wire). You just need to make sure the total volume of all conductors doesn't exceed the volume of the box.

Yes, it is perfectly fine to have two different circuits and/or two different gauge wires in the same box.

Code actually REQUIRES you to tie all ground wires together, even when they're on different circuits. And if this is a metal box, don't forget to install a #12 bonding jumper to the box and tie that in to all of the ground wires.

even at an inch deep that's 16 square inches, so I would be stuffing at worst 6.25 square inches. Heck my box is 2 inches deep, I cannot imagine putting enough cables there to take up the full allowance.

Thank you for taking the time to respond, most appreciated.

 

[exranger06]

even at an inch deep that's 16 square inches, so I would be stuffing at worst 6.25 square inches. Heck my box is 2 inches deep, I cannot imagine putting enough cables there to take up the full allowance.

Thank you for taking the time to respond, most appreciated.

No, you're not calculating properly. When you take two wires and splice them together with a wire nut, that counts as TWO wires. You said you're taking three #12 cables and splicing them all together, and splicing two #14 cables together. Each cable has a hot leg and a neutral, so you have a total of six #12 wires, and four #14 wires. Then you add in one more #12 wire for the ground wires, so basically seven #12s and four #14s. That comes out to (2.25 x 7) + (2.0 x 4) = 23.75 cu in.

 

[u2slow]

IMHO, do a lighting JB, and another JB for receptacles.

 

[75gmck25]

Using two junction boxes makes it easier in the future when you want to add one more receptacle or one more light. And that 2nd junction box probably only costs less than $5, so its not a cost consideration. Unless you have a space issue (nowhere to put the 2nd box), I don't understand why you would not use two.

Bruce

 

[Don1357]

No, you're not calculating properly. When you take two wires and splice them together with a wire nut, that counts as TWO wires. You said you're taking three #12 cables and splicing them all together, and splicing two #14 cables together. Each cable has a hot leg and a neutral, so you have a total of six #12 wires, and four #14 wires. Then you add in one more #12 wire for the ground wires, so basically seven #12s and four #14s. That comes out to (2.25 x 7) + (2.0 x 4) = 23.75 cu in.

Thank you! I would have never caught that if I didn't bring it up!

I love being proved wrong, it guarantees I learn something

Using two junction boxes makes it easier in the future when you want to add one more receptacle or one more light. And that 2nd junction box probably only costs less than $5, so its not a cost consideration. Unless you have a space issue (nowhere to put the 2nd box), I don't understand why you would not use two.

Bruce

Oh, trust me; I'm putting an obnoxious number of outlets from the get go, and that doesn't even count all the other receptacles dedicated to machines that will be running from the breaker box. If by any chance I were to need another outlet I would run it from the nearest existing outlet, not this box.

Same thing with the lights; these are for the overhead lights, a total of 8 x 4' LED lights. If I needed to add another set of 4 they would run off the existing wiring coming out of the box. I see it as a safety thing not to share the wiring for the shop lights with anything else; the last thing you want is to be working on a hand-eating machine and have the lights go out because somebody else tripped something.

 

[Terry D]

Just use two j-boxes, one for each circuit

 

[Skiff Builder]

Live it up ( if you have the space). Get 2 each of these, pleasure to splice in with all the room.
I use thes for my outlets too- just add a mud ring.

 

[sberry]

I agree, for diy kind of stuff use 2 boxes.

 

[Terry D]

Live it up ( if you have the space). Get 2 each of these, pleasure to splice in with all the room.
I use thes for my outlets too- just add a mud ring.

Just to let you know, that cover or mud ring will not fit on that 2-gang box.You need this kind of box


https://www.homedepot.com/p/Carlon-...ork-Electrical-Wall-Box-B432ARR-UPC/100404123

 

[Skiff Builder]

Just to let you know, that cover or mud ring will not fit on that 2-gang box.You need this kind of box


https://www.homedepot.com/p/Carlon-...ork-Electrical-Wall-Box-B432ARR-UPC/100404123

Got it Terry D. I use what you posted. Guess I grabbed a wrong pic online to post. Thks,

 

[M-Petrik]

This weekend I'm running two wires to the upstairs of the garage, one for lights, one for outlets. The lights will be on 14 to supply the 3 or so amps for the 40 Watt LED 4' lights will draw. The outlets are 12 wire for 15 amp outlets.



The plan is to run the two wires to a 4" junction box from where the wire for the light is just spliced out, the one for the outlets is spliced into two branches to go left and right. According to what I could research the box is big enough for this? And that there are no problems having the two different wires, which I plan on clearly labeling?



Bonus question: Is it ok to just tie the ground wires together or do they need to keep separate grounds? The plan is to keep them separated but I'm just curious if it is kosher to just merge them.

Why are you over sizing your wire for the 15a receptacles? You only need #14 for 15a.


Sent from my iPhone using Garage Journal

 

[sparky 1971]

Why are you over sizing your wire for the 15a receptacles? You only need #14 for 15a.


Sent from my iPhone using Garage Journal

15 amp receptacles can be installed on a 20 amp circuit. He does not state that is what he's doing, but it's more than likely what is happening.

OP, if you haven't done the project already, I would suggest just using a regular 4X4 box with an extension box on it.

 

[sberry]

I am still a fan of 2 boxes up in an attic? Is there a real reason to force it in to one? Nothing is good as 1 circuit in a box.