4" x 2-1/8" junction box capacity

[quakerj]

I studied up on electrical codes while doing my workshop project, but I think I overlooked one thing-- box fill. I thought it was done by volume, but it appears it's done by # of wires and wire size.

I have a 4"x2-1/8" junction box that has a 3/4" and 1/2" EMT going to it from the panel; feeds electrical to basically 2-1/2 sides of the shop, all #12 wires. The 3/4" EMT is pretty well full, 9 current carrying conductors, one neutral that carries only unbalanced load of a MWBC. So ten wires there, and then the 1/2" EMT has 6 wires, only 4 of which are considered current carrying. In a nutshell, 16 wires pass through this J-box, it basically just distributes wires from the panel to different conduits. They pass through cleanly and take up very little space in the box.

Despite that, I think I just read that this size box can only accommodate 13 #12's. The wires are already run and it would be a disaster if I had to start pulling things out and redoing it. I think there are stackable boxes you screw on top of an existing J-box which will increase volume, is this a possible remedy for my situation? Or something more clever I don't know about? Or perhaps I'm misinterpreting the code and am completely mistaken.

Either way if someone could provide some insight on this, I'd sure appreciate it.

 

[inphx]

In general, a 4" x 2-1/8" junction box can accommodate a maximum of 12 14-gauge wires or 8 12-gauge wires. Since you have 16 wires in the box, including both 14-gauge and 12-gauge wires, it is not up to code.

Section 314.16, covers the fill requirements for electrical boxes.

 

[quakerj]

In general, a 4" x 2-1/8" junction box can accommodate a maximum of 12 14-gauge wires or 8 12-gauge wires. Since you have 16 wires in the box, including both 14-gauge and 12-gauge wires, it is not up to code.

Section 314.16, covers the fill requirements for electrical boxes.

Is this information outdated, or am I reading it wrong / misinterpreting it? This is definitely something I should have looked into more!

Also, is adding one of the box extenders (that increases depth) an allowable way to increase volume and meet code?

 

[sparky 1971]

I wouldn't worry about it, but if you are really concerned, a box extension is acceptable. You will also gain a couple of cubic inches depending on what box cover or mud ring goes on. If it's a blank cover, nothing will be gained though.

 

[quakerj]

I wouldn't worry about it, but if you are really concerned, a box extension is acceptable. You will also gain a couple of cubic inches depending on what box cover or mud ring goes on. If it's a blank cover, nothing will be gained though.

In the practical world I live in, I couldn't possibly energize all 16 wires to capacity given I only have 90A service to the workshop, plus the fact it's residential and only one or two people would be working in there at one time.

I could understand the volume thing, I've seen junction boxes stuffed so full of wire nuts the cover was bent outward, and they probably meet code because of number of wires. But this is not one of those, just a pass-through. I figured if 16 wires are allowed in a 3/4 EMT (only 9 can be current carrying in that small conduit), surely 16 wires could safely pass through a 4x2-1/8" J-box and still meet code, but seems I was wrong.

But I'm doing my best to research and do it right, so if I sell the house one day, a home inspector doesn't flag something that looks way off base. We're supposed to get electrical permits and inspections, but way out here in the county nobody does. But I'd like it to meet code provided I don't have to rip a bunch of stuff out.

 

[sparky 1971]

In the practical world I live in, I couldn't possibly energize all 16 wires to capacity given I only have 90A service to the workshop, plus the fact it's residential and only one or two people would be working in there at one time.

I could understand the volume thing, I've seen junction boxes stuffed so full of wire nuts the cover was bent outward, and they probably meet code because of number of wires. But this is not one of those, just a pass-through. I figured if 16 wires are allowed in a 3/4 EMT (only 9 can be current carrying in that small conduit), surely 16 wires could safely pass through a 4x2-1/8" J-box and still meet code, but seems I was wrong.

But I'm doing my best to research and do it right, so if I sell the house one day, a home inspector doesn't flag something that looks way off base. We're supposed to get electrical permits and inspections, but way out here in the county nobody does. But I'd like it to meet code provided I don't have to rip a bunch of stuff out.

I promise you that a home inspector has no clue as to what box fill is. Even if one did, nobody is going to take the cover off to see how many wires are passing through. For the electrical part of a home inspection, they kind of know about GFCI's, double tapped breakers, and missing knockout seals for panels and exposed boxes. Some might know that romex can't be stapled to the bottoms of ceiling joists.

You can always throw a $2 box extension on and forget about it.

 

[quakerj]

I promise you that a home inspector has no clue as to what box fill is. Even if one did, nobody is going to take the cover off to see how many wires are passing through. For the electrical part of a home inspection, they kind of know about GFCI's, double tapped breakers, and missing knockout seals for panels and exposed boxes. Some might know that romex can't be stapled to the bottoms of ceiling joists.

You can always throw a $2 box extension on and forget about it.

That's along the lines of what I was thinking, I appreciate the confirmation. So if I do throw a $2 box extension on, does that solve the problem? Is there a formula for box volume versus number of wires? Nearly all I could find on Google/internet had to deal with Romex/NM cables and plastic boxes like you'd find in a house.

I'm just going to leave it as is for now because I know it will work fine, but I'd like to know of a sure remedy if need it in the future.

 

[sparky 1971]

That's along the lines of what I was thinking, I appreciate the confirmation. So if I do throw a $2 box extension on, does that solve the problem? Is there a formula for box volume versus number of wires? Nearly all I could find on Google/internet had to deal with Romex/NM cables and plastic boxes like you'd find in a house.

I'm just going to leave it as is for now because I know it will work fine, but I'd like to know of a sure remedy if need it in the future.

It's all based on volume and the extension will solve all of your problems and concerns. For what it's worth, I've never had an inspector question box fill. I can't think of a time one has even looked inside a box at the rough in when everything is open.

There isn't really a formula but a #14 is counted as ? cubic inches, #12 is X cubic inches, devices are another amount, clamps are also figured. I haven't done a box fill calculation in close to 30 years, to be honest I don't even remember how.

 

[yatg]

There's an app for that

Box Fill Calculator - Apps on Google Play

Calculate electrical box fill in a snap.

play.google.com

no idea how well it works

 

[Zeke]

I would use a box extension just to accommodate make up. I have a hard time with 6 wires. I buy a lot of 4S boxes and/or 2-gang boxes.

 

[mike93lx]

I had a really good home inspector for my last purchase that was really detailed and thorough. But nothing besides the panel gets opened. If you have work that looks like you care about workmanship, no one will bat an eye.

If everything fits fine I would skip the extension and move on.

 

[quakerj]

If everything fits fine I would skip the extension and move on.

After reading this thread, that's exactly what I'm going to do. I just finished installing all the outlets and buttoning everything up in the panel. I still have to finish running overhead lighting and put a welder outlet where my 6ga circuit is run to, also perhaps an EMT run direct to my 2-post lift instead of a cord. Here's some pics of the progress. This is absolutely my first rodeo, so if anyone sees anything amiss, please let me know.

I made heavy use of MWBC because I was limited on conduit fill in places, and MWBC is an easy way to knock a few neutral wires off the 9 current carrying conductor limit in 3/4" EMT. It also allows me to to swap 120V boxes for 240V 20A outlets if I ever need to, or extend the branch circuits without worrying about capacity. The downside is I'll have some extra money ******* in GFCI breakers and/or GFCI receptacles. I installed GFCI in what I felt were vulnerable locations, but I'll have to go back through and replace some additional outlets with GFCI (or use breakers) to be fully up to code.

 

[quakerj]

Couple more pics...

 

[Zeke]

It would be nice if you did offsets next to the boxes and used some EMT nail straps.

 

[quakerj]

It would be nice if you did offsets next to the boxes and used some EMT nail straps.

Not sure what you mean, can you elaborate?

 

[sparky 1971]

It's a little (about 3/8") offset that puts the conduit against the surface so a one or two hole strap can be used. You are supposed to have the pipe supported within 3' of a box. I don't see how you're supposed to use a nail in strap with metal framing though.

 

[mike93lx]

It's a little (about 3/8") offset that puts the conduit against the surface so a one or two hole strap can be used. You are supposed to have the pipe supported within 3' of a box. I don't see how you're supposed to use a nail in strap with metal framing though.

I got you

 

[sparky 1971]

I got you

I forgot about those. Good idea. Do they make them that fit these?

 

[mike93lx]

I forgot about those. Good idea. Do they make them that fit these?

 

[Norcal]

Where are your GFCI's? All 15A & 20A 120V receptacles require them in shops/garages/outbuildings, under the 2017 NEC, and under the 2020 NEC 240V ones require it too. Multi wire circuits make it a expensive proposition to add them.

 

[quakerj]

Where are your GFCI's? All 15A & 20A 120V receptacles require them in shops/garages/outbuildings, under the 2017 NEC, and under the 2020 NEC 240V ones require it too. Multi wire circuits make it a expensive proposition to add them.

I covered that in one of my last posts:

The downside [to MWBC] is I'll have some extra money ******* in GFCI breakers and/or GFCI receptacles. I installed GFCI in what I felt were vulnerable locations, but I'll have to go back through and replace some additional outlets with GFCI (or use breakers) to be fully up to code.

You have to understand I'm doing this myself, balancing this with a 40+ hour a week job. It'll get done and I assure you nobody will get electrocuted in the meantime. I'm taking my time and being thorough as possible.

As it stands, I currently have GFCI outlets installed anywhere under 4', garage door circuit, and anything near the entry door. The rest will get there. No 2020 code here, we're still on 2017.

A side question if I do decide to use GFCI breakers, does Siemens make a plug-in-neutral dual-pole GFCI? The only dual-pole ones I can find have the neutral pigtail...

 

[quakerj]

It's a little (about 3/8") offset that puts the conduit against the surface so a one or two hole strap can be used. You are supposed to have the pipe supported within 3' of a box. I don't see how you're supposed to use a nail in strap with metal framing though.

Thanks for that, I missed the 3' requirement. I've been using conduit clamps/hangers (pictured) throughout that keep the pipe elevated about 3/4" (?) off the surface. I'll place an extra one nearer to the boxes, should be an easy fix.

 

[sparky 1971]

Thanks for that, I missed the 3' requirement. I've been using conduit clamps/hangers (pictured) throughout that keep the pipe elevated about 3/4" (?) off the surface. I'll place an extra one nearer to the boxes, should be an easy fix.

Those will work fine. I use a similar product by Caddy that doesn't require the bolt. One strap will work for both 1/2 and 3/4. They are pricey little bastards for no more than what they are though.

Nvent Caddy Conduit Clip, Spring Steel 812M | Zoro

Order Nvent Caddy Conduit Clip, Spring Steel, 812M at Zoro.com. Great prices & free shipping on orders over $50 when you sign in or sign up for an account.

www.zoro.com

 

[sparky 1971]

Git 'R Done

 

[Norcal]

I covered that in one of my last posts:


You have to understand I'm doing this myself, balancing this with a 40+ hour a week job. It'll get done and I assure you nobody will get electrocuted in the meantime. I'm taking my time and being thorough as possible.

As it stands, I currently have GFCI outlets installed anywhere under 4', garage door circuit, and anything near the entry door. The rest will get there. No 2020 code here, we're still on 2017.

A side question if I do decide to use GFCI breakers, does Siemens make a plug-in-neutral dual-pole GFCI? The only dual-pole ones I can find have the neutral pigtail...

Under the 2017 NEC, GFCI's are required for ALL 15A, & 20A, 120V, receptacles with no exceptions even for ceiling mounted ones, all exceptions went away many editions of the NEC ago. GFCI receptacles are somewhat cheap, 2-pole GFCI breakers are not.

 

[quakerj]

Under the 2017 NEC, GFCI's are required for ALL 15A, & 20A, 120V, receptacles with no exceptions even for ceiling mounted ones, all exceptions went away many editions of the NEC ago. GFCI receptacles are somewhat cheap, 2-pole GFCI breakers are not.

Once again, this is understood.

 

[exranger06]

A 4" x 4" x 2.125" box has an internal volume of 30.3 cu in. So if you add up the volume of all of your conductors, they cannot exceed 30.3 cu in. It doesn't matter if the conductors are current carrying conductors or not, they all count. Except for ground wires, which are handled a little differently. Each #12 wire uses 2.25 cu in. Assuming none of those are ground wires, 16 x 2.25 = 36 cu in. You'll need to add a box extension to bring it up to code. That's also assuming that all of the wires just pass right through the box with no splices. A wire that passes straight through with no splices counts as one wire. But if you cut the wire and splice it back together with a wire nut, it now counts as 2 wires.

 

[Zeke]

A 4" x 4" x 2.125" box has an internal volume of 30.3 cu in. So if you add up the volume of all of your conductors, they cannot exceed 30.3 cu in. It doesn't matter if the conductors are current carrying conductors or not, they all count. Except for ground wires, which are handled a little differently. Each #12 wire uses 2.25 cu in. Assuming none of those are ground wires, 16 x 2.25 = 36 cu in. You'll need to add a box extension to bring it up to code. That's also assuming that all of the wires just pass right through the box with no splices. A wire that passes straight through with no splices counts as one wire. But if you cut the wire and splice it back together with a wire nut, it now counts as 2 wires.

Good, simple explanation of the code.

 

[quakerj]

A 4" x 4" x 2.125" box has an internal volume of 30.3 cu in. So if you add up the volume of all of your conductors, they cannot exceed 30.3 cu in. It doesn't matter if the conductors are current carrying conductors or not, they all count. Except for ground wires, which are handled a little differently. Each #12 wire uses 2.25 cu in. Assuming none of those are ground wires, 16 x 2.25 = 36 cu in. You'll need to add a box extension to bring it up to code. That's also assuming that all of the wires just pass right through the box with no splices. A wire that passes straight through with no splices counts as one wire. But if you cut the wire and splice it back together with a wire nut, it now counts as 2 wires.

That's exactly what I needed, many thanks for that info.

 

[quakerj]

Question of the day since GFCI topic got brought up:

This last weekend I replaced all my standard 120V outlets with GFCI where they needed to be. So 9 additional GFCI outlets were placed, less expensive (and less labor on my part) than more conduit runs which would have been required to meet code if I chose to run an extra neutral in lieu of MWBC. And dual pole GFCI breakers are still prohibitively expensive. No big deal.

My question is does a GFCI outlet need a dedicated ground wire / pigtail to the box? If I'm not mistaken you can omit the ground wire if you have at least two screws bonding the outlet to a metal box, which in turn is grounded by the metal conduit. I could verify this on traditional outlets, they had a metal back that was clearly attached to both screws AND the ground terminal. The GFCI, the ground screw is bonded to the top metal attachment/screw, but it's plastic on the back, so I can't visually verify a connection to the bottom attachment point. I used a meter and got zero resistance from top and bottom screw points. So evidently they're bonded so I omitted the ground wire. Plugging in one of those 3 light outlet testers verifies a proper ground. All that said, did I do this correctly and to code?

Installing a ground wire wouldn't be impossible but due to the size of two GFCI outlets in a 4" box would make for a tight fit, so I'd rather avoid it.

 

[Copymutt]

Re: inspection. In Co. you are required to have a pre cover inspection & a final so overfill would be visible.
Is there any deviation in code for push in connectors vs wire nots for fill specs?

 

[quakerj]

Re: inspection. In Co. you are required to have a pre cover inspection & a final so overfill would be visible.
Is there any deviation in code for push in connectors vs wire nots for fill specs?

I'm pretty sure the use of push in connectors makes no difference as it pertains to box volume. Splice is considered a splice which you have to account for in your wire count. Someone correct me if I'm wrong, but this is how I interpreted it.

 

[exranger06]

If the receptacle is self-grounding, you don't need to connect a ground wire to it (only if mounting in a grounded metal box, of course). If it's not self-grounding, then you need to connect a ground wire. This is true for all receptacles and switches, not just GFCIs. Watch this video for more info:

 

[quakerj]

If the receptacle is self-grounding, you don't need to connect a ground wire to it (only if mounting in a grounded metal box, of course). If it's not self-grounding, then you need to connect a ground wire. This is true for all receptacles and switches, not just GFCIs. Watch this video for more info:

Thanks for that. I think my GFCI installation checks all the boxes without the ground jumper.

All the outlets have the brass self grounding insert on one side, and even though the outlets mount to covers, all are metal with at least two screws affixing them to metal boxes. I don't see anything in that code section which would preclude me from installing this way.

 

[Poolshark314]

Are you replacing EVERY outlet with GFCI? You should only need to replace the first outlet on each branch circuit to protect all downstream outlets.

 

[quakerj]

Are you replacing EVERY outlet with GFCI? You should only need to replace the first outlet on each branch circuit to protect all downstream outlets.

No not replacing every outlet, just the ones that are required to be.

 

[mike93lx]

No not replacing every outlet, just the ones that are required to be.

Lol.

One per circuit or multiple?

You can protect an entire circuit with one gfci. I can't imagine a situation where you would need 30 gfci's other than installing more than necessary

 

[Poolshark314]

Yeah you only need to replace the first outlet with GFCI to protect all outlets downstream of it. Sounds like you could save some money reducing your GFCI's

 

[quakerj]

Lol.

One per circuit or multiple?

You can protect an entire circuit with one gfci. I can't imagine a situation where you would need 30 gfci's other than installing more than necessary

Yes there's just one per circuit, didn't count but think there's 10 or 11 total. The total cost for the GFCIs when bought in contractor pack were not much more than the cost of ONE dual pole GFCI breaker, so it only made sense.

If I need additional outlets in the future, indeed they'll be protected by the load side of an existing GFCI outlet.

 

[mike93lx]

Yes there's just one per circuit, didn't count but think there's 10 or 11 total. The total cost for the GFCIs when bought in contractor pack were not much more than the cost of ONE dual pole GFCI breaker, so it only made sense.

If I need additional outlets in the future, indeed they'll be protected by the load side of an existing GFCI outlet.

Got it. I must have been thinking about another recent thread regarding the comment on 30 gfci's.

Carry on!