Floor box depth

[charlie b]

A high-end dwelling unit will have lots of windows, and therefore many receptacles in the floor to satisfy the NEC spacing requirements. The owner doesn't want to see the outlets. An architect wants to conceal the floor outlets by use of a removeable wood outlet cover. There is limited space (2-5/8") between the bottom of the wood flooring and the top of the concrete slab. I am being asked whether they need to recess the slab at the outlet locations, in order to have room for the outlet box. So, just how deep are these outlet boxes? Can they fit within the 2-5/8" available space?

TIA.

 

[mgookin]

A high-end dwelling unit will have lots of windows, and therefore many receptacles in the floor to satisfy the NEC spacing requirements. The owner doesn't want to see the outlets. An architect wants to conceal the floor outlets by use of a removeable wood outlet cover. There is limited space (2-5/8") between the bottom of the wood flooring and the top of the concrete slab. I am being asked whether they need to recess the slab at the outlet locations, in order to have room for the outlet box. So, just how deep are these outlet boxes? Can they fit within the 2-5/8" available space?

TIA.

Is the concrete already there?

 

[charlie b]

No. Construction has not yet begun.

 

[mgookin]

No. Construction has not yet begun.

Than how about asking structural if they can give you some locations where you can have a niche to recess a box?

(if it's not precast)

 

[charlie b]

I apparently wasn't clear about my question. There is no problem getting some extra space in the locations already shown on the floor plans. The question is, do I need more than 2-5/8" to get a box installed between the top of the slab and the bottom of the wood floor? If so, how deep do I have to tell the architect to make the recess?

 

[mgookin]

You were clear. My reading was clouded I missed the part where you said "I am being asked whether they need to recess the slab at the outlet locations, in order to have room for the outlet box."

Looking at steel city boxes they come in 1-1/2" and 2-1/8" deep. What I'm not finding is the depth from the back of the KO to the rear surface of the box. It appears to be a short distance which means if you recess the box more than 1/4" or so, your emt is going to be in a pickle. Probably safer with the 1-1/2" box.

Are EC's on here ok with the 1-1/2" deep box for a duplex receptacle?

Charlie I'm assuming you're spec'ing EMT for this job with metal boxes. If not, there are comparable plastic boxes available.

 

[Ponchik]

I would use a 4" square box with a plaster ring.
Then again I dont know if the regular 4s box can be installed in concrete. :?

 

[kwired]

I would use a 4" square box with a plaster ring.
Then again I dont know if the regular 4s box can be installed in concrete. :?

A listed floor box/cover assembly would be necessary, not any generic device box.



Which box is used may depend on how the thing is to be "concealed" per the owners request.

I have seen floor boxes that may be close to being shallow enough, but they don't really have enough volume for feed-thru conductors in them.

If the "concealing" involves a trap door or similar, maybe a "floor box" is no longer necessary? May want to run such a thing by the AHJ as well to prevent rejection later.

There are other compact outlet devices out there that may be able to fit in small spaces in the walls if normal outlet devices will not work. Plugmold at the base of the wall, probably not desired but a possible option as well. Or a good 'ol cord pendant receptacle from the ceiling- only needs to be 5-1/2 feet from the floor to comply with 210.52

 

[Ponchik]

A listed floor box/cover assembly would be necessary, not any generic device box...........

I would think the cover has to be floor rated not box. Am I not correct on that?

Carlon has the following that look like a generic wall box but do have the proper floor cover plate.

View attachment 13900

 

[kwired]

I would think the cover has to be floor rated not box. Am I not correct on that?

Carlon has the following that look like a generic wall box but do have the proper floor cover plate.

View attachment 13900

IIRC for that Carlon box and a few other similar out there the box comes in a kit with the cover and is not a standard wall box. Cover will not work so well on a standard wall box.

 

[Strathead]

I would think the cover has to be floor rated not box. Am I not correct on that?

Carlon has the following that look like a generic wall box but do have the proper floor cover plate.

I think you are not quite right. The box that goes in the floor may be the same box as any other, but it would still need to be tested and listed for the application, I believe. The point for the OP though is to determine what the architect intends the finish product to look like and work back from there.. Perhaps a box with a tile cover, they have a small rim, and a recess to put the tile, carpet or in this case wood in so that very little of the cover is seen.

 

[kwired]

Perhaps a box with a tile cover, they have a small rim, and a recess to put the tile, carpet or in this case wood in so that very little of the cover is seen.

I was going to suggest that, don't know if there are small boxes for a single receptacle out there or not. Only ones I have seen are larger boxes for stage power or other applications where the cover may be at least 12 x 12 or larger.

 

[mgookin]

... An architect wants to conceal the floor outlets by use of a removeable wood outlet cover. ...
TIA.

I believe they want to have continuous flooring until the receptacle is need (which may be never). If the receptacle is needed, the occupant will remove the small section of flooring to provide access to the receptacle.

OP needs to know if he can get a box & receptacle in that 2-5/8" high cavity between the top of slab and bottom of flooring. That raises the question of whether the flooring is an acceptable cover for the receptacle or if he needs another cover under the flooring, in which case he may (or may not) need to accommodate additional dimension for same.

 

[Dennis Alwon]

I would have them recess a space. Most floor boxes are 3 or 3.5" deep. One could drill it out but it would be easier not to have to do that. Some of those floor receptacles are recessed into the box similar to a clock receptacle

 

[Strathead]

I believe they want to have continuous flooring until the receptacle is need (which may be never). If the receptacle is needed, the occupant will remove the small section of flooring to provide access to the receptacle.

OP needs to know if he can get a box & receptacle in that 2-5/8" high cavity between the top of slab and bottom of flooring. That raises the question of whether the flooring is an acceptable cover for the receptacle or if he needs another cover under the flooring, in which case he may (or may not) need to accommodate additional dimension for same.

If this is the case then I would just install one gang floor boxes in the concrete pour with a listed cover. It would be the 2-5/8 below the final finished floor, and then they could remove the floor and reach down if they needed to access.

 

[steve66]

Is it on grade? I'd probably be tempted to just put the boxes in the slab - flush with the top of the slab.

If its above grade, is a poke-through an option? That puts all the wiring under the slab.