Furred block wall

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nizak

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Trying to find the best way to install receptacles on 3/4" firred block walls.

Will be having 1/2" drywall cover.

I'm able to get 1.25" deep boxes which will work with 3 #14 conductors and the device.

I won't pass inspection with NM cable.

Will aluminum MC cable meet requirements? Does it still need to be set back 1.25" off the face of the firring strip?

Was thinking 1/2" emt but that will stick out beyond the firring by 1/8"

Any help appreciated.
 
Is the block wall already built?
If not, can you be on site as it is built to rough boxes into the wall with a deep enough device ring to flush out to the drywall? Sounds like a 1-1/4 ring would work.

Edit: forgot about the thickness of the block, probably need about a 2" deep ring
 
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nizak said:
Trying to find the best way to install receptacles on 3/4" firred block walls.

Will be having 1/2" drywall cover.

I'm able to get 1.25" deep boxes which will work with 3 #14 conductors and the device.

I won't pass inspection with NM cable.

Will aluminum MC cable meet requirements? Does it still need to be set back 1.25" off the face of the firring strip?

Was thinking 1/2" emt but that will stick out beyond the firring by 1/8"

Any help appreciated.
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On first reading I thought fired block walls, but then again I thought you mean douglas fir wood strips.

Reading further it seems you mean to say "furring strips". :cool:

If walls are not built yet I usually install stub out drops through bricks hollow core. If already built do a surface emt installs.
 
NM and MC cable have the same 1.25" setback requirements unless the MC is run through holes in metal studs. According to T314.16(A) you can install 9-#14 conductors in a 4X4X1.25" box. You can also add the 1/2" raised cover volume if so marked.
 
nizak said:
......Does it still need to be set back 1.25" off the face of the firring strip?.
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You have to be 1.25 away from the edge of the framing. Don't confuse that with being 1.25 away from the front face of the framing. That means you can come down the middle between the furring strips and be 7" away from the framing.

That being said I would beg and plead for 1.5" furring is anybody is in a mood to be reasonable.
 
Dave.

Not following you with the 7" dimension.

I have 3/4" thick furring strips that are Ram set to existing cinder block walls.

If I attach MC cable directly to the block, that puts me approx. 1/4"(assuming o.d. Of cable about 1/2") behind the front edge of the strip.

Isn't that a code violation unless there is some type of strike plate installed over the entire length of the cable from the box to the ceiling?
 
Ok.

I get the 7" dimension(duh...)

Must be the afternoon in and out of the cellulose filled attic ?that made me stupid.
 
nizak said:
Dave.

Not following you with the 7" dimension.

I have 3/4" thick furring strips that are Ram set to existing cinder block walls.

If I attach MC cable directly to the block, that puts me approx. 1/4"(assuming o.d. Of cable about 1/2") behind the front edge of the strip.

Isn't that a code violation unless there is some type of strike plate installed over the entire length of the cable from the box to the ceiling?
Click to expand...

NM or MC can run anywhere between the furring strips including right next to it (stapled to the side of it in fact). You only need nailing plates where you cross a furring strip horizontally. The drywallers are going to use the furring strips to screw down the drywall. They should not be putting screws anywhere else. If you are going to run MC, I would use MC one hole straps tapconed and just stay midway between the furring straps.

When I run boxes in block, I cut 4.5x4.5" holes in the block with a diamond saw on an angle grinder and set deep 4x4 boxes in the holes. I use Caddy screw gun brackets cut down so the box ends up with a big ear on each side. Just tapcon the ear to the block. Fast and easy, plus the deep box has plenty of room. The box is flush with the block. Just put an appropriate mud ring on to get it flush with the drywall. I run NM with my boxes so you might have to make a bigger hole for the MC to exit the block.
 
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nizak said:
Dave.

Not following you with the 7" dimension.

I have 3/4" thick furring strips that are Ram set to existing cinder block walls.

If I attach MC cable directly to the block, that puts me approx. 1/4"(assuming o.d. Of cable about 1/2") behind the front edge of the strip.

Isn't that a code violation unless there is some type of strike plate installed over the entire length of the cable from the box to the ceiling?
Click to expand...

We had a big long discussion on this subject awhile back. The consensus was that the 1-1/4" rule can be interpreted to apply horizontally as well. So if you keep your cable at least 1-1/4" from the side of the stud or furring strip you are in compliance. That said I don't like it one bit when it comes to furred out walls for the reason you mention. Maybe your AHJ will see it that way too. My opinion is that any contractor that furs out concrete with 1x material has no regard for the electrical that has to follow. AFAIC they should make him frame out the wall with 2x4s in front of the concrete so that you have the full 3-5/8 to work with.

-Hal
 
hbiss said:
We had a big long discussion on this subject awhile back. The consensus was that the 1-1/4" rule can be interpreted to apply horizontally as well. So if you keep your cable at least 1-1/4" from the side of the stud or furring strip you are in compliance. That said I don't like it one bit when it comes to furred out walls for the reason you mention. Maybe your AHJ will see it that way too. My opinion is that any contractor that furs out concrete with 1x material has no regard for the electrical that has to follow. AFAIC they should make him frame out the wall with 2x4s in front of the concrete so that you have the full 3-5/8 to work with.

-Hal
Click to expand...

I agree with Hal the 1.25" dimension apply laterally away from the furring strip as well. I also agree that using 3/4" furring strips is a poor installation method. At the minimum 1 5/8" metal studs should be used which would make the room less than 2" smaller.
 
infinity said:
I agree with Hal the 1.25" dimension apply laterally away from the furring strip as well. I also agree that using 3/4" furring strips is a poor installation method. At the minimum 1 5/8" metal studs should be used which would make the room less than 2" smaller.
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Air conditioning costs here are a big expense. Most of time when I see block walls furred out there is no insulation which makes absolutely no sense to me. I worked on one addition that had 3/4" foam board installed between the furring strips. Better than nothing I suppose. (I had to trench through it to run wire.)

Recently I was working on plans for my own new house. I wanted high energy efficient walls which my research said means the walls should have R40 insulation (R13 is standard). The best way to get R40 walls is 10" of mineral wool between the block and the studs i.e. a large gap between the stud wall and the block.

Makes the electrical installation a breeze :D.
 
hbiss said:
We had a big long discussion on this subject awhile back. The consensus was that the 1-1/4" rule can be interpreted to apply horizontally as well. So if you keep your cable at least 1-1/4" from the side of the stud or furring strip you are in compliance. That said I don't like it one bit when it comes to furred out walls for the reason you mention. Maybe your AHJ will see it that way too. My opinion is that any contractor that furs out concrete with 1x material has no regard for the electrical that has to follow. AFAIC they should make him frame out the wall with 2x4s in front of the concrete so that you have the full 3-5/8 to work with.

-Hal
Click to expand...

Playing Devil's advocate here: If I installed a second furring strip butted up against the first and stapled my NM to the side of it I would be compliant. But then the inspector might say that the second furring strip is actually the first furring strip so not compliant. But If I painted the second furring strip red to indicate it belongs to the electrical installation just like I would paint a ceiling wire supporting a lay-in fixture then I should be compliant. Correct? I would just have to convince the drywallers to not screw into the red one.
 
Good luck with that. You can't even rely on them to not put screws in the middle of a bay, completely missing the stud. That's the main reason why I feel 1x furred walls shouldn't be allowed if there is going to be electrical in them.

-Hal
 
Inform owners how much extra labor will be involved to cut out blocks to allow for boxes that have needed volume for what will be installed in them, and possibly to better protect the wiring in this shallow cavity and they will figure out that 1.5" furring strips is not much more then .75" furring strips. 1.5" inch boxes with mud rings are a lot more versatile then anything that will fit in .75" furring construction.
 
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