Can you use a light or receptacle box as a junction box?

[Do_it_yourself]

I'm looking at how best to minimize EMT conduit clutter in my new shop. I have two questions: 1) Is it acceptable to run wire from a separate circuit through the the box of a light or receptacle in order to use that wire on another device farther down the conduit? Can a light box be used as a junction box? I realize that there must be enough room in the box for all of the wires. 2) I purchased a book on wiring that has a table showing wire capacities of EMT, It references NEC 2005, Annex C, Table C1. This table shows that 1/2" EMT can hold only 4 - 12ga THHN wires. Am I missing something, as every other table I can find on this subject says I can run 9 - 12ga wires? Thank you!

 

[Mustang51js]

Yes you can use the light box as a j-box

 

[Mustang51js]

I don't have my code book with me but you may be looking at the wrong table or type of wire,the 9 sounds right

 

[sands35]

J boxes need to be accessible. So light boxes work great if you are putting a blank cover on them through drywall.

 

[Do_it_yourself]

Wow, you guys are GREAT! What quick responses! I will be using the light and receptacle boxes to hang the lights and install receptacles and will pass, in some instances a wire from another circuit through them, headed down stream to power another device. I should have stated that these will be hung on unfinished walls and completely accessible. I'm attaching a copy of the table to which I was referring. I completely believe the 9 wire response and should just move on, but this table is a mystery to me.

 

[Zeke]

I believe it makes a difference whether the wires run straight through or are spliced. At least it should. I could look that up, but I'll let the pundits speak.

 

[pattenp]

The max of nine #12 THHN in 1/2" EMT is correct.

 

[Baada]

1) Is it acceptable to run wire from a separate circuit through the the box of a light or receptacle

Not against code but some would say it is bad form to have more than one circuit in the same junction box. I believe the theory is that when someone turns off one breaker if that someone doesn't know there is more than one circuit they would falsely believe that the whole junction box was off and safe to work on. Which one could argue they should check with a meter or similar before working to be sure anyway but I digress.

 

[Eriehunter]

Not against code but some would say it is bad form to have more than one circuit in the same junction box. I believe the theory is that when someone turns off one breaker if that someone doesn't know there is more than one circuit they would falsely believe that the whole junction box was off and safe to work on. Which one could argue they should check with a meter or similar before working to be sure anyway but I digress.

Typically not bad form or against any code, it is very common and done everyday. If this were the case it would make running conduit a worthless exercise as that is what condiut is intended for.... it has to go to a box sometime.

I always like to write the panel name (where there is more than 1 panel) on the junction box cover as well as what circuits are contained in the box so it makes turning off circuits easier when the need arises later to work on them.

And always check to make sure power isn't present before performing any work, and still treat it like it is hot.

 

[Do_it_yourself]

Thanks guys, I appreciate all of the input! I have run Romex in the past, but not EMT and have had no need to pass a wire thru a receptacle box headed to another device. But using EMT it makes you think a little differently. I hope I am making myself clear in what I want to do. I have two circuits running inside EMT, I head off in one direction with both runs, I use one of those runs to connect a series of receptacles and continue the other run in the same conduit and pass thru the rear of each receptacle box and use it to wire another series of receptacles farther down the wall. Wouldn't that be fine?

 

[Elmo4895]

If you need more room in the junction box you can buy a box extender at any electrical supply house. I doubt that you will need more room with just two circuits though. Most wiring jobs require more than one circuit in a pipe run.

 

[CoopVA]

Nothing wrong with what you want to do. We do it all the time.


Sent from my iPad using Tapatalk

 

[alfredeneuman]

I purchased a book on wiring that has a table showing wire capacities of EMT, It references NEC 2005, Annex C, Table C1. This table shows that 1/2" EMT can hold only 4 - 12ga THHN wires. Am I missing something, as every other table I can find on this subject says I can run 9 - 12ga wires? Thank you!

The book you purchased is wrong.
I looked up the table and it says 9 THHN #12s in a 1/2"

The same table says that 4 THHW are allowed to be in a 1/2"
The difference between the thickness of the insulation of the 2 is huge

 

[Do_it_yourself]

Thank you everyone for your responses, I believe that answeres my questions. I believe I'll put a big X thru the table in my new book!

 

[Mike F]

Not so fast with that "X" in the book. Your book does not say only 4 THNN wires, it says only 4 12-gauge THW,THHW,THW-2 wires. And as Alfredneuman points out, the thickness differences of the 2 insulations is huge. At least that's how I read the table.

 

[Kevin C]

I was curious so I did a bit of searching. The table is a reprint of the 2005 code, but the issue is how its applied.

I got this from Mike Holts Forum:

Note (1) says "see" the annex, not "use" the annex. The
annexes are not part of the code, and not enforceable.
(see the first text in italics at the beginning of Annex C.)

......

It looks like you are "safe" using the lower number in the
annex, but if there is any discrepancy, the numbers from
Chapter 9 (including application of all Table Notes) are
the correct #'s.

http://forums.mikeholt.com/showthread.php?t=107602

From 90.3ccccc
...Annexes are not part of the requirements of this Code but are included for informational purposes only.

http://forums.mikeholt.com/showthread.php?t=129227&page=2

In short, the table is really conservative fill recommendation that you don't have to follow and might help if you dont want to calculate fill ( or go thought the real code section). It seems that it causes a lot of confusion since it does not agree with the code. Seems like a page that should get removed.

 

[shampoop]

Wow, you guys are GREAT! What quick responses! I will be using the light and receptacle boxes to hang the lights and install receptacles and will pass, in some instances a wire from another circuit through them, headed down stream to power another device. I should have stated that these will be hung on unfinished walls and completely accessible. I'm attaching a copy of the table to which I was referring. I completely believe the 9 wire response and should just move on, but this table is a mystery to me.

Make sure you research and understand the difference between conduit fill and box fill calculations.

Conduit fill is pretty simple and straight forward, especially when the same gauge wire is used with the same insulation.

Box fill is pretty convoluted.

 

[Do_it_yourself]

I was curious so I did a bit of searching. The table is a reprint of the 2005 code, but the issue is how its applied.

I got this from Mike Holts Forum:



http://forums.mikeholt.com/showthread.php?t=107602



http://forums.mikeholt.com/showthread.php?t=129227&page=2

In short, the table is really conservative fill recommendation that you don't have to follow and might help if you dont want to calculate fill ( or go thought the real code section). It seems that it causes a lot of confusion since it does not agree with the code. Seems like a page that should get removed.

I'll have to agree with that, seems very confusing.

 

[Do_it_yourself]

Make sure you research and understand the difference between conduit fill and box fill calculations.

Conduit fill is pretty simple and straight forward, especially when the same gauge wire is used with the same insulation.

Box fill is pretty convoluted.

Yeah I have seen the calculations. I don't plan on running very many wires at all thru any of the conduit or boxes. I also plan on using a lot of oversized boxes and maybe conduit as well. But I probably will need to do the calcultions on a box or two.

 

[Mustang51js]

Wow, you guys are GREAT! What quick responses! I will be using the light and receptacle boxes to hang the lights and install receptacles and will pass, in some instances a wire from another circuit through them, headed down stream to power another device. I should have stated that these will be hung on unfinished walls and completely accessible. I'm attaching a copy of the table to which I was referring. I completely believe the 9 wire response and should just move on, but this table is a mystery to me.

You need to find the table that shows thhn stranded for #12. For some reason that table is for something else. Chapter 9 table 8 if I remember right, someone correct me if I'm wrong, I'm to lazy to go out to my van now lol

 

[alfredeneuman]

Chapter 9 Table 8 is "Conductor Properties"

Tables 1 through 5A deal with calculating the number of conductors allowable in the conduits.

Annex C is just those calculations applied.

 

[Baada]

Typically not bad form or against any code, it is very common and done everyday. If this were the case it would make running conduit a worthless exercise as that is what condiut is intended for.... it has to go to a box sometime.

I always like to write the panel name (where there is more than 1 panel) on the junction box cover as well as what circuits are contained in the box so it makes turning off circuits easier when the need arises later to work on them.

And always check to make sure power isn't present before performing any work, and still treat it like it is hot.

That's interesting to know. I'm not a professional by any means but I was told by my inspector specifically that while not a code violation he considered it a bad practice and enthusiastically discouraged me from doing so when I pulled a few permits for my basement and kitchen remodel. He appeared to be implying I wouldn't pass inspection if I did it. Since it wasn't a big deal for me I did as recommended by him. I have been told by several contractors that the inspectors in my area are some of the hardest to please so that just may be their thing. Thanks for setting me straight.