Switch / Receptacle Box Typical Size

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ron

Senior Member
Architect wants to put receptacles and switches recessed in a shallow framed wall.

I normally do not size the boxes, but Arch wants to know how shallow can the framed wall be outside face to rear of cavity (depth of a device box).

Maybe just see if my thought process is right.

These will be 20A circuits, but I will not show exact wiring on my drawing and it will be left up to the EC, so when I calculate a typical device box size per 314.16(B), I'm imagining one circuit per box and some devices will feed through to another recept or switch. If they want to put more than one circuit in that area, then it will be routed in separate boxes. If they want to "T" tap a circuit, they will be forced to run the long way.

So I calculated for a typical run (2) conductors for incoming, (2) for outgoing, (1) ground, (1) internal clamps (MC cable), (2) device. For (8) "#12AWG conductors", I get 8 x 2-1/4 = 18CuIn. If that is correct, then the standard device box for 18in^3 is 3"x2"x3-1/2".

So dimension from outside face of wall surface to rear of wall cavity, would be 3-1/2". Or do I need to tell them 4" to be safe?
 

iwire

Moderator
Staff member
Location
Massachusetts
I would suggest no less than 1.5" inside the wall cavity.

For the circuit you described you could use a 1.5" 4" square box with appropriate single gang plaster ring.

This way you will get the volume you need side to side instead of front to back.

Something like this

27241d1393143805-plaster-ring-opinion-needed-p_scw_168_05.jpg
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
So I calculated for a typical run (2) conductors for incoming, (2) for outgoing, (1) ground, (1) internal clamps (MC cable), (2) device. For (8) "#12AWG conductors", I get 8 x 2-1/4 = 18CuIn. If that is correct, then the standard device box for 18in^3 is 3"x2"x3-1/2".

If I were looking at open framing and four MC cables at an opening, my first thought would be to use a generic 4" square metal junction box (so-called 1900 box) and a plaster ring. It's a lot shallower.
 

iwire

Moderator
Staff member
Location
Massachusetts
Never saw those before in a 4 x4, only octagons. Thanks.

The company uses thousands of that exact box, I do not like them. The clamps can short out the MC if you are not careful. I prefer external clamps and when I am ordering that is what I use.
 

ron

Senior Member
I would suggest no less than 1.5" inside the wall cavity.

For the circuit you described you could use a 1.5" 4" square box with appropriate single gang plaster ring.

This way you will get the volume you need side to side instead of front to back.

Something like this

27241d1393143805-plaster-ring-opinion-needed-p_scw_168_05.jpg

Thanks for the info and especially the picture.
 

timmer.79

New member
How about chiseling out whatever is behind the wall that your framing up and put yourself a deep box in and you won't have to worry about fighting to shove a GFCI or dimmer switch into a shallow box that's full of wire.

Sent from my XT1093 using Tapatalk
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I would suggest no less than 1.5" inside the wall cavity.

For the circuit you described you could use a 1.5" 4" square box with appropriate single gang plaster ring.

This way you will get the volume you need side to side instead of front to back.

Something like this

27241d1393143805-plaster-ring-opinion-needed-p_scw_168_05.jpg



I would request a little more than 1.5" of depth and as you've suggested use a metal box. That box would require more like 1.75" of depth in the wall cavity. A true 1.5" depth would require a 1.25" deep box.
 

iwire

Moderator
Staff member
Location
Massachusetts
I would request a little more than 1.5" of depth and as you've suggested use a metal box. That box would require more like 1.75" of depth in the wall cavity. A true 1.5" depth would require a 1.25" deep box.

OK, I assumed the small size studs where 1-1/2 because we use 1-1/2" boxes in them with no trouble.

After doing some checking the smaller size studs we call 1-1/2" are actually 1-5/8".

lgmf-stud.gif

http://www.archtoolbox.com/materials-systems/metals/lgmf.html

The set up I suggested works fines in the small stud sizes.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
OK, I assumed the small size studs where 1-1/2 because we use 1-1/2" boxes in them with no trouble.

After doing some checking the smaller size studs we call 1-1/2" are actually 1-5/8".

lgmf-stud.gif

http://www.archtoolbox.com/materials-systems/metals/lgmf.html

The set up I suggested works fines in the small stud sizes.

I was thinking about when wood studs are used on the flat side attached to masonry, in those installations the 1.5" deep box with adapter cover won't work.
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
I was thinking about when wood studs are used on the flat side attached to masonry, in those installations the 1.5" deep box with adapter cover won't work.

Maybe I can't picture your thought that it won't work.

But if the box is 1.5" and the stud is 1.5" then why won't it work? You also have a 1/2" or 5/8" sheetrock on top so either of the P-rings will work. You also have 1/4" and flat P-rings that can be used.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Maybe I can't picture your thought that it won't work.

But if the box is 1.5" and the stud is 1.5" then why won't it work? You also have a 1/2" or 5/8" sheetrock on top so either of the P-rings will work. You also have 1/4" and flat P-rings that can be used.

If you look at the photo that Bob posted, post #2, the box itself is 1.5", add on the thickness of the adapter cover and the heads on the 8/32 screws and the sheetrock will bow out at the stud if you use a wood stud mounted on it's side.
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
If you look at the photo that Bob posted, post #2, the box itself is 1.5", add on the thickness of the adapter cover and the heads on the 8/32 screws and the sheetrock will bow out at the stud if you use a wood stud mounted on it's side.

I have never placed a straight edge on the finished sheetrock surface to see if the 8-32 screws made any difference.
 

peter d

Senior Member
Location
New England
The company uses thousands of that exact box, I do not like them. The clamps can short out the MC if you are not careful. I prefer external clamps and when I am ordering that is what I use.

Same here, I like to buy the 4" square with side bracket and knock outs and use my own connectors. It also reduces stock. :cool:
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
If you look at the photo that Bob posted, post #2, the box itself is 1.5", add on the thickness of the adapter cover and the heads on the 8/32 screws and the sheetrock will bow out at the stud if you use a wood stud mounted on it's side.
The generic Raco 189 in my hand, with a single gang 1/2 " ring on it mics out at exactly 1.75 " from the back of the back to the crest of the 8/32 cover screws.

The thickness of the steel box back + the thickness of the ring + the thickness of the cover screw heads all add to the interior box depth of 1.5 ".

That extra 1/4 " will play havoc with the flatness of the wall if it is proud of the framing face. Whether it is proud will be entirely a function of how tight the 1.5" stud is to the masonry wall.
 

jumper

Senior Member
The generic Raco 189 in my hand, with a single gang 1/2 " ring on it mics out at exactly 1.75 " from the back of the back to the crest of the 8/32 cover screws.

The thickness of the steel box back + the thickness of the ring + the thickness of the cover screw heads all add to the interior box depth of 1.5 ".

That extra 1/4 " will play havoc with the flatness of the wall if it is proud of the framing face. Whether it is proud will be entirely a function of how tight the 1.5" stud is to the masonry wall.

Proud?
 
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