Wiring in block walls?

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tedge

Senior Member
Location
Camden, ME
I'm bidding on 4 bath/shower buildings, all built with concrete block walls. I've never wired anything in block walls, so I'm looking for some guidance. I assume that I would cut a hole into the empty air space in the block and attach a box somehow. For those of you who do this sort of work, how do you attach/secure your boxes? How does one sneak a full length peice of EMT down into the secured box on an outside wall where the roof sheathing is in the way? Any guess as to a percentage of extra time involved as compared to wiring with MC in sheetrock? Thanks in advance.
 

cadpoint

Senior Member
Location
Durham, NC
You have to work in the masons terms, you need to work with them,
usually they will run 4 courses of block a day, they might do other.

A course is 7 5/8" with 3/8" mortor joint *(per ED) X 4 and is usually the SOP.

I've only worked EMT for an approx. 2'-6" length for ease of the brick mason, and tape each end, I've seen higher, but it comes down to working with my the mason, if you work with them they will easily remove a block when you might spot an error, as opposed to long sticking them, JMO.

You'll need deeper mud rings, and don't forget the power for motion paper towel dispensor ...
I'd also duct tape your boxs if they filling the blocks..
 
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DAWGS

Senior Member
Location
Virginia
Install your boxes and conduit as the block goes up. The brick mason will cut the block around your box. Make sure you use masonry boxes. Install your conduit in 3' lengths as the mason runs his block courses. They just lift the block over the conduit, and generally dont want to be lifting blocks more than 3-4'. When you get to the ceiling just 90 stub your conduit out, or offset out of block.
 

tedge

Senior Member
Location
Camden, ME
Ok, so it sounds like a lot of wasted time sitting around waiting for the masons. Hmmm... These buildings are very basic, so there's not a lot of boxes to put in. Allthough most will be at the same height, so they'll be done on the same day.

So they generally fill the voids after the blocks are up? That's what holds the boxes in place then? Should I secure them temporarily somehow until the voids are filled?
 

fireryan

Senior Member
Location
Minnesota
They will mud the box in place but its nice if you fill the voids under your boxes with some cardboard or small pieces of block because its easier for them to mud in the box that way. Its best to stay on the masons good side as they can make the job a living hell for you
 

fireryan

Senior Member
Location
Minnesota
If the block walls are already up you can fish a flex down and then mud the boxes in yourself. I have seen some guys use shims to secure the box in place but im not sure how dependable that is? Anyone else do that or not?
 

cadpoint

Senior Member
Location
Durham, NC
tedge said:
Ok, so it sounds like a lot of wasted time sitting around waiting for the masons. Hmmm... These buildings are very basic, so there's not a lot of boxes to put in. Allthough most will be at the same height, so they'll be done on the same day.

So they generally fill the voids after the blocks are up? That's what holds the boxes in place then? Should I secure them temporarily somehow until the voids are filled?

Seems you never worked with a mason. To get your conduits to a circuit service point or correct for a run, plus cut your conduits for your boxes. OK say your bored.

With all the extra's of all your circuits all at one elevation, don't be the only one there that hour.

If your good the second conduit can be ready with an offset can be ready to be set in place for them, use math and go with a about a EOC of 10" from box.
 

tedge

Senior Member
Location
Camden, ME
The blocks aren't up, it is only at the bidding stage. I'm just trying to get an idea on the work involved so I can make an accurate estimate.

Cadpoint- No I haven't worked w/ a mason before. I see them building chimneys and rock walls, but there's not a lot of block buildings going up in my area. So I should plan on having a couple of guys there to keep ahead of them eh? Pardon my ignorance, but why would I need to make offsets? Couldn't I just come straight down the void w/ my conduit sections into the top of the box? Am I missing something?
 

Minuteman

Senior Member
You won't need offsets with a deep masonry box. Cut your EMT into 3' lengths or so, that way the mason can set blocks over top. Be ready to add another EMT section. Use raintight fittings and wrap them and the boxes with duct tape. Usually, this is something that an apprentice handles. When it's time for another piece, the mason will be sure to call for the apprentice (and raz him a little). :smile:
 

wawireguy

Senior Member
I'd use PVC in the walls to your boxes. Bring a heat gun in case you have to make some bends in your PVC. You can put tie wire through the holes in the back and wrap it around a 6" piece of pvc to hold your box out. You'll want to be there when they grout and hold your box in to make sure the grout doesn't push it out. Put ground pigtails in now in case the back of the box gets grouted.
 

480sparky

Senior Member
Location
Iowegia
tedge said:
Ok, so it sounds like a lot of wasted time sitting around waiting for the masons. Hmmm... These buildings are very basic, so there's not a lot of boxes to put in. Allthough most will be at the same height, so they'll be done on the same day.

So they generally fill the voids after the blocks are up? That's what holds the boxes in place then? Should I secure them temporarily somehow until the voids are filled?

If the brickies are worth their salt, trust me.... you won't be wasting much time. Usually, a good brick crew will be hard to keep up with. And if you don't, they won't have any qualms about going on without you. Plan your box layout, have everything ready to go the day before they start laying block. Msons get paid for laying block, not waiting for the electrician. If you end up ticking the brickies off, you'll end up with mud (mortar), coins or pebbles in your conduit.

As for securing the boxes, most brickies are nice enough to place a scrap chunk of CMU behind your box to wedge it in, then they fill in around the box with mud.
 
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infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The last bunch of brickies I worked with installed the boxes as the walls went up. They would layout the first course (usually the foreman) on one day and then start the block the next day. After the first course went down we would do our layout on the face of the block. We would also prefab 4 11/16" boxes with connectors, 30" EMT stubs and duct tape over the 2" mud ring. Then we would lay them out at the locations that we had marked on the block. As the courses went up the brickey would cut out a block with his wet saw and mud the prefab boxes right in. After he got up a few courses we would go back and install a 30" piece of EMT. and repeat the process. For several boxes all at the same height we would prefab them together with nipples in between so he could set two or three at a time with only one stub up.

Working well with the brickies can make a huge difference in your production.
 

tedge

Senior Member
Location
Camden, ME
So 2" mudrings on 4 11/16 boxes is the way to go huh? I was thinking that the voids wouldn't be big enough for a box that size.

I was told today by the GC I would be working for, that he put in their scope that they were to do the boxes and add the sections of pipe as they went. I just need to have everything on site and laid out. Thanks for all the replies.
 
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mdshunk

Senior Member
Location
Right here.
tedge said:
I was told today by the GC I would be working for, that he put in their scope that they were to do the boxes and add the sections of pipe as they went. I just need to have everything on site and laid out. Thanks for all the replies.
That's fine and dandy, in concept, but you really don't want them doing that. Just plan on that language in their scope to more or less assure their cooperation, but you still need to do it yourself.
 

wawireguy

Senior Member
I'd just use masonry boxes or 4 square, deep/shallow w/ deeper mudrings. Want to say 1 1/2"? You should have a variety of boxes on hand to deal with different situations like rebar or other unseen issues.

Another thing you can usually stub out the bottom to if you want to or need to.. Run in the slab or out below grade.
 

220/221

Senior Member
Location
AZ
1. Use deep masonary boxes and duct tape the opening.

2. Pre fab all your boxes with connectors and 32"-48" PVC stubs.

3. Install ground screws and pigtails BEFORE installation. It is a helluvalot easir when they are in your hand.

4. Bring donuts for the Brickies.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
tedge said:
So 2" mudrings on 4 11/16 boxes is the way to go huh? I was thinking that the voids wouldn't be big enough for a box that size.

Actually it depends on the type of block that they're using. Some block has larger hollow cells than others. This particular job the cell was about 5" wide and the block face about 2" thick so a 4 11/16" box fit like a glove.
 
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