This video link provides a short video of how to cut for an electrical box in an Omni Block stretcher block. Notice that the ideal placement of the electrical box is in the center of the block.
All of the electrical is installed as the wall is erected, which is one of Omni Block’s significant system advantages. All electrical materials are standard items and should be available at any electrical parts wholesaler. An abbreviated electrical parts list is linked here. These parts are the recommended parts as they have been identified and repeatedly used because they fit perfectly within the block.
The video at top right shows an assembled Steel City STC 52173/4 box (4 square 2 1/8 deep box 3/4 knockouts) with an STC 52C50 mud ring (4 square single gang 1 1/2″ tile ring). The electrician has preassembled and attached a Carlon PVC 3/4″ adaptor (threaded 3/4 PVC terminal adaptor) so that the mason can cut for the electrical box and place in a noted location in the Omni Block wall. The electrician is not required to be on site when the boxes are placed if proper instruction is provided to the mason of each boxes specific location.
The other electrical box option that has become popular and is more frequently used is a Steel City GW135G single gang 3.5″ deep box . This box can be easily made into a two or three gang box in the field by removing the side plates and attaching the boxes together. Please see this animated link at right that shows the electrical box attached to a 3/4″ PVC adaptor.
Important Note: Electrical parts that are deemed “close” to these recommendations by an electrician unfamiliar with Omni Block will not work for one reason or another. It is important that a first-time user at least use the recommended parts the first time through the project and this would include 3/4″ rigid PVC conduit. It is strongly suggested to not use flexible conduit of any kind.
All electrical that is required in the first 4 foot grout lift should be noted on the slab (red arrow) at the start of masonry for the mason to clearly see. This photo shows an under window application.
These standard electrical symbols indicate boxes that are to be installed at 16” top-of-box within the wall, which is a standard electrical box height and is also the top of the second course.
1 Single gang 110v outlet with vertical conduit
2 Single gang 110v outlet with horizontal left conduit (pictured at left)
3 Single gang low voltage outlet with vertical conduit
4 Single gang low voltage outlet with horizontal left conduit
These symbols indicate electrical boxes to be installed at 48” top-of-box (standard height) which is also the top of the block at the 6th course.
5 Single gang 110v switch with vertical conduit
6 Double gang 110v switch with two vertical conduits
7 Triple gang 110v switch with three vertical conduits
8 The electrical parts should be on site before the start of masonry.
9 Once the electrical is noted on the slab, a count can be made to indicate how many block need to be pre-cut.
10 An electrical box is used as a template. The interior boxes should be placed in the center of the stretcher block or at the edge of two stretcher block allowing for the 3/8″ mortar joint. The exterior boxes should be cut immediately next to the exterior cross web of the block. These locations are important because the vertical conduit run above the boxes will be clear of any subsequent block cross webbing.
11 A variety of saws with a diamond blade may be used to accurately cut for the electrical box.
12 Chip out any remaining debris.
13 Insert electrical box to test fit each block and then place at the noted locations on the slab so that the mason can readily and appropriately place it in the wall.
If block is to be exposed, more care in the cutting of the boxes is required so that saw cuts do not extend past the electrical cover plate. The job pictured is not exposed block so the saw cuts beyond the box will be covered with drywall compound before an electrical cover plate is installed.
The most common electrical application is a single gang box that is located in the center of the interior side of the stretcher block. The electrical box shown is a 4” square box with 3/4” knock-outs attached to a 1 1/2” tile ring. The 3/4” knock-outs are important because 3/4” conduit is used.
Notice that the back of the box is abutted to the middle lineal wall of the block, which renders it impossible for the box to move once it is installed.
There are numerous electrical box configurations available to meet every electrical requirement.
14 Two single-gang boxes installed at 16” top-of-box, which is a standard height.
15 These two single-gang boxes, with block above, are set side-by-side because one is a 110v and the other is low voltage. Per Code 110v and low voltage wiring must be run in separate conduit and cannot be housed within the same box.
All boxes are set flush to the face of the block.
All boxes must have an NEC approved grounding wire attached to them.
16 Single-gang box installed at 48” top-of-box, which is the standard switch height and at the top of the 6th course.
17 Double-gang box installed at 48” top-of-box, which is the standard switch height.
18 Horizontal conduit stubbed out of the block at an interior stud wall location so that an electrician can “fish” wiring from that point to the electrical boxes contained within the block wall.
These slides illustrate a detailed process of a box-to-box installation on one wall to another box on an adjacent wall.
19 Measure and cut the PVC conduit.
20 Snap the short inserts in half (horizontally) and place them in the cells under the conduit.
21 Glue the male PVC conduit end and slide it inside the Female PVC adapter.
A single-gang 110v outlet box is now installed with no vertical conduit because the box is run in a “series”. The conduit on one side is attached to another single-gang 110v outlet box along the wall. The conduit on the other side is “swept” to an adjacent wall using a 90° PVC sweep, then connected to another single-gang 110v outlet box. Eventually, one box must either have a vertical conduit attached to it or the horizontal conduit is run out of the wall (see 18 above). The electrician can then “fish” his wiring from box-to-box.
Overview of two single-gang outlet boxes run in “series” connecting to a third single-gang outlet box (not shown).
Once these boxes are installed, the mason is “done” with this electrical.
An additional advantage of conduit run horizontally from box-to-box is that additional future boxes can be rather easily added by first cutting into the block and then into the conduit. New wiring can then be “fished” within the existing conduit.
Electrical Meter Illustration
