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Old 08-19-2008, 09:09 PM   #1
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Junction box in patio ceiling


I have an addition that has 2 sets of 12/2 wires being ran to the panel.

One set is for the 125v requirements (recepts and lights)
The other set is for 2 1000w 220v baseboard heaters.

I need a junction box to tie in the 2 sets of 12/2 wG romex to the outdoor pvc junction box with THHN run in conduit. This junction box needs to be in the ceiling of the connecting patio, which is open air. My question is can I use a regular 2-gang plastic blue old work with a blank cover or must I use something exterior-rated. The patio ceiling is dried-in with t-111 as the ceiling.


According to my figures, I have 2.25 x 8 (for the 12 romex) plus 2.25 for the connected grounds totaling 20.25, so a 2 gang seemed like plenty for space fill.

...again, I am concerned it the NM box is ok.

Thanks for any advice.

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Old 08-19-2008, 09:25 PM   #2
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Junction box in patio ceiling


I am going to assume that you are currently running the 2 sets of 12/2 back to the panel and that this wiring is not existing. Any wire used outside must be rated for wet location. No exposed romex may be used, and any wiring run in conduit must be wet location rated "W" (THWN). You cannot run romex through the conduit, it must be individual conductors.

No you cannot use a blue pvc box with plastic conduit in a outdoor setting. They make plastic PVC boxes designed for this very purpose. Also, your PVC pipe must be the gray electrical rated, not the white "plumbing" pipe.

Box fill only takes into consideration the "Current Carrying Conductors" this means only the neutrals and hots, ground wires do not count towards box fill. Also, it should be noted that you only need to count the wires that enter/exit the box, pigtails to devices do not count.


Hope this helps...

Correction: ground wires DO count only as one entity.

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Last edited by theatretch85; 08-20-2008 at 12:30 AM. Reason: Correction
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Old 08-19-2008, 09:33 PM   #3
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Junction box in patio ceiling


i thank you for your response theatretch85, but I have always understood that conduit could accept romex. Let me state the the conduit is being run above ground attached to brick veneer with anchors and screws.

I have also been told that I count all the grounds as one unit, in my case 2.25 for 12 guage.

But I suspected that I had to use "wet location".

I am glad I came on this forum to get straightened out.

My problem is that I wanted the box recessed.

-thanks again.
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Old 08-19-2008, 10:04 PM   #4
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Junction box in patio ceiling


Calculating box fill is a requirement so that "Boxes and conduit bodies shall be of sufficient size to provide free space for all enclosed conductors." (NEC, 314.16).

Ground wires do count towards box fill (NEC, 314.16(B)(5)), and it makes sense because of course, they do occupy space. The idea of "current-carrying conductors" is used in circuit ampacity calculations for derating purposes, which is correct in that the grounds are not counted since they are not normally current-carrying conductors.

For box fill, grounds counted as one unit for all of them, unless an isolated ground set is also present - then the isolated ground set would be counted again as a separate unit. The unit size used for each ground set is based on the largest equipment grounding conductor that is present in the box for that set.

20.25 cu in. is the correct volume allowance required.
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Old 08-20-2008, 12:00 AM   #5
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Junction box in patio ceiling


I stand corrected on the box fill. Sorry I was thinking of the current ampacity in derating.

The issue of whether romex (NM) is allowed to be used in conduit or not has been discussed on this site before, I must not be searching for the right terms; and browsing through my 2008 NEC code book, I am not finding the right material either.

I will post back when I find the thread related to this topic.

Update: Found the thread just after submitting this post....

"Common Path" limits for Romex -- Code question

Last edited by theatretch85; 08-20-2008 at 12:03 AM. Reason: Found thread...
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Old 08-20-2008, 08:08 AM   #6
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Junction box in patio ceiling


The 2 sets of 12/2 would only be inside conduit for about 12" just to feed into the junction box. The romex is already stapled to the bottom truss chord (celing joist) of the patio and the patio is covered. I am only trying to make a splice and I know I need the splice to be accessible.

***let me also add that there is to be another splice right outside the addition fascia that will be wet location gray pvc and the wiring from that point will be 12 THWN.***

The other problem (inconvenience really) is that I had preferred the junction box to be recessed into the ceiling with a cover blank showing instead of the clumpy gray box protruding.

I am still confused as to why I need a "wet location" (or rain tight) box when the area in question will never directly be exposed to rain or snow.

Plus, based on your answer, if I wanted light fixtures in the ceiling, then I must use some type of wet location light box? I was told that I could use recessed light cans. But I did not see where recessed light cans were "wet location". So if I can use light cans recessed into the ceiling, why can't I use a 2gang blue NM box in the same ceiling?

I am really confused now...

Last edited by I_think_I_conduit; 08-20-2008 at 08:12 AM.
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Old 08-20-2008, 08:28 AM   #7
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Junction box in patio ceiling


Quote:
Originally Posted by I_think_I_conduit View Post
I am still confused as to why I need a "wet location" (or rain tight) box when the area in question will never directly be exposed to rain or snow.

Plus, based on your answer, if I wanted light fixtures in the ceiling, then I must use some type of wet location light box? I was told that I could use recessed light cans. But I did not see where recessed light cans were "wet location". So if I can use light cans recessed into the ceiling, why can't I use a 2gang blue NM box in the same ceiling?
Yours is at least a damp location, so your wiring methods and materials need to be rated for damp locations. BTW, NB (Romex) is NOT allowed in wet or damp locations. You would need to use conduit or UF cable.

What does "The patio ceiling is dried-in..." mean? If your patio doesn't have a normal roofing method or material, it would probably need to be built as a "wet" location.

From 2008 NEC:
Location, Damp. Locations protected from weather and not subject to saturation with water or other liquids but subject to moderate degrees of moisture. Examples of such locations include partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subject to moderate degrees of moisture, such as some basements, some barns, and some cold-storage warehouses.

Location, Dry. A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction.

Location, Wet. Installations underground or in concrete slabs or masonry in direct contact with the earth; in locations subject to saturation with water or other liquids, such as vehicle washing areas; and in unprotected locations exposed to weather.

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Last edited by williswires; 08-20-2008 at 08:31 AM. Reason: added text
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