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Outlet Boxes


In construction wiring, switches and electrical receptacles (known as wiring devices) are mounted in boxes which are secured to the wall, ceiling or floor. The box protects the device from damage and gives access to the wiring even after construction is complete. Once the box is installed and wired, the device is mounted and connected to the conductors. Finally, a box cover is installed to prevent accidental contact with conductors in the box.


Manufacturers of electrical equipment make boxes for every conceivable application. Some are used only in residences. Others are intended for commercial and industrial jobs. The National Electrical Code and your local code dictate the type of boxes that may be used in your community.


The size of the outlet box or junction box is determined by the size and number of conductors to be installed, and the size of the wiring device needed. When a plaster ring or switch ring is to be set against the box, the box size, the type, and the number of wiring devices to be used determine the size of the ring. The depth of the plaster ring or the switch ring will vary with the thickness of the final wall finish.


Boxes with plaster rings can be installed in ceilings and walls in wood construction, unit masonry, tile or concrete. Special outlet boxes and special plaster and switch rings are made for unit masonry and tile work. The ring depth is greater so the ring lip is flush with the surface of the finished wall. Check the architectural details of the plan to be sure you're pricing the right box and plaster ring. Some types cost considerably more than the standard grade used on most jobs.


This section does not deal with outlet boxes used in hazardous installations. Hazardous conditions require special outlet boxes and fittings that are approved for special environments.

Handy Boxes


Outlet Boxes

Handy boxes are generally intended for surface mounting, though some are made with brackets attached that permit flush mounting. Handy boxes are 2" wide by 4" high. They come in 1-1/2", 1-7/8", 2-1/8" and 2-13/16" depths. The box is one-piece sheet metal with knockouts on all sides and the back. The tapped ears for adapting devices are turned inward into the box.


The boxes and covers for handy boxes are plated steel. The covers are stamped. Cover types include blank, single switch, single receptacle, duplex receptacle, four-wire twist-lock receptacle, and despard device with three knockout squares. Price labor and material cost for the wiring device separately.


Handy boxes have punched holes for mounting with round-head wood screws, round-head machine screws, dome-head stove bolts, tie wire or masonry anchors.

Sectional Switch Boxes



Sectional Switch Boxes


Sectional switch boxes are generally installed flush with the wall in wood frame walls. The finish surface can be either plaster, drywall, insulating board or paneling. The boxes can be ganged together by removing side panels. They're made of plated steel with punched holes for mounting. Boxes can have knockouts in all sides and back or may have Romex or MC clamps for holding the cable in place.


Sectional boxes are made 2", 2-1/2" and 2-3/4" deep. The tapped mounting ears are turned outward away from the box opening and the ears are spaced for standard wiring devices. Sectional switch boxes can be mounted in the wall or ceiling with round head wood screws, round head machine screws, dome head stove bolts, tie wire or masonry anchors. Be sure your electricians set the box flush with the level of the finished surface.

Welded Switch Boxes



Welded Switch Boxes


Welded switch boxes look like sectional boxes. The difference is that they can't be ganged by removing the side panels. They're made with Romex or MC clamps for holding the cable in place.


Welded switch boxes are available with mounting brackets attached to the sides for rough-in mounting to the construction framing. The boxes are stamped, welded, punched, plated steel. The mounting ears are turned outward away from the box opening and are spaced for mounting standard wiring devices. The box can be mounted with nails, round-head wood screws, round-head machine screws, dome-head stove bolts, tie wire or masonry anchors.


Welded switch boxes come in single gang or two gang. They're 2-1/2", 2-13/16" or 3-13/16" deep.


Octagon boxes are one-piece pressed plated steel boxes. They're punched for knockouts and mounting and are available with mounting brackets that are attached to the box for flush mounting in a wall or ceiling.


The box's diameter is either three (called 3-0) or four (called 4-0) inches. The mounting ears are turned inward into the box for mounting covers or fixtures. The boxes can be mounted on fixed or adjustable bar hangers which are nailed to the framing. The box is attached to the bar hanger with dome-head stove bolts or round-head machine screws.


Some bar hangers have a 3/8" fixture stud for securing the lighting fixture directly to the bar hanger for support. The center knockout is removed from the box, the fixture stud is inserted into the box through the removed knockout, and a 3/8" locknut is used to secure the box to the stud.


Octagon boxes are 1-1/2" or 2-1/8" deep. A very shallow box called a pancake box is also made in 3-0 and 4-0 sizes. The pancake box is used when space is restricted and only one circuit is needed.


Another octagon box is used in concrete construction. Octagon concrete rings are stamped plated steel and are generally used in overhead concrete construction. The rings have 1/2" and 3/4" knockouts and mounting ears that turn into the box for adapting a top cover and finish cover or lighting fixture. The box has tabs for nailing to concrete forms.


The octagon rings are 2-1/2", 3", 3-1/2", 4", 5" or 6" deep. The top cover can be blank with 1/2" or 3/4" knockouts or the cover can be purchased with a fixture stud attached for mounting a lighting fixture directly to the stud. Octagon concrete rings are 4-0.


The smallest square box is 4" x 4" x 1-1/2" deep. It can be either a one-piece unit or welded, stamped plated steel. The box has 1/2" or 3/4" knockouts or comes with a combination of 1/2" and 3/4" knockouts. The 4-S box can be purchased with mounting brackets and with Romex or MC clamps.


4-S boxes are also made 2-1/8" deep with the same knockouts as a 4-S by 1-1/2" box.


The tapped ears are in diagonal corners and have 8-32 tapped holes for attaching a cover or an extension ring. There are punched holes for mounting the box to the framing. Machine screws come with the box.


The extension ring is 1-1/2" deep with 1/2" or 3/4" or a combination of 1/2" and 3/4" knockouts. The bottom diagonal corners have cutouts for mounting to the 4-S box. The top has tapped ears in diagonal corners with 8-32 tapped holes for attaching a cover. Again, machine screws come with the box.


4-S boxes are also made with two sets of mounting ears and 6-32 tapped holes for mounting two wiring devices. These two-ganged 4-S boxes can be purchased with mounting brackets for flush construction. 4-S boxes make good junction boxes in conduit systems. They're used for interior, dry, accessible locations and can be used in concrete walls or ceilings if the mounting holes are covered to keep liquid concrete from filling the box. When used in concrete construction, the point where conduit enters the box should be sealed to keep concrete out of the conduit.


Another square box is the 4-11/16" x 4-11/16" box. It's made the same as the 4-S box except that knockouts in the 2-1/8" deep box can be 1/2", 3/4", 1" or 1-1/4". Combinations of knockouts are 1/2" and 3/4", 1" and 1-1/4". It has four tapped tabs for mounting a cover or an extension ring. The tapped holes are for 10-32 machine screws, which come with the box.


4-11/16" boxes can be purchased with flush mounting brackets. They're used for interior, dry, accessible locations.


Bar hangers support an outlet box that has to be placed between two framing members. They're offset to allow for the depth of the box. Two lengths are available: one for nailing to studs 16" on center; the other for nailing to studs 24" on center.


There are two types of bar hangers. One comes with stove bolts for attaching the box to the bar hanger. The bar hanger has one long slot for adjustment or centering the box. The stove bolts are passed through the box and through the slot in the bar hanger. A square nut is used for tightening each bolt, thus securing the box to the bar hanger in the correct position.


The other type bar hanger has a 3/8" fixture stud that can be moved on the bar hanger. This permits adjustment of the box position. The center knockout is removed from the back of the outlet box, a 3/8" fixture stud is inserted into the box and a 3/8" locknut is used to secure the box to the bar hanger in the position desired.


Non-metallic outlet boxes are made of either fiberglass or PVC in shapes and sizes like sheet metal boxes.


Fiberglass outlet boxes are generally used in residential concealed wiring. Many come with nails in place in a bracket for attaching to studs or joists. They have threaded metal inserts placed for standard wiring devices. Both 3" and 4" diameter boxes are available. These boxes use fiberglass covers that are similar to steel covers made for steel boxes.


Fiberglass switch boxes are available in single-gang, two-gang, three-gang and four-gang. They all can be purchased with or without mounting brackets and Romex clamps.


Fiberglass 4-S boxes are either 1-5/8", 2-1/4" or 2-1/2" deep. Many covers and plaster rings are available. These are also made of fiberglass.


Another series of non-metallic outlet boxes is made of PVC plastic. These are generally used for surface wiring but can be flush mounted. The switch boxes resemble FS condulets except that they don't have threaded hubs. PVC hubs are threadless because PVC conduit is glued or cemented in place. Other PVC boxes are made as junction boxes. They can be installed in concrete and are approved for corrosive conditions. But they're not acceptable for hazardous environments.


Special covers are available for PVC boxes. Most are weatherproof. There are blank covers, single receptacle covers, duplex receptacle covers, single switch covers and ground fault interrupter (GFI) covers.


I've described many of the common types of outlet boxes. But other types are available. What's listed here is representative of what's stocked by most dealers. Unless you handle a lot of exotic applications, this section has covered nearly all the boxes you use regularly.

Electrical, electrician

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Phone: (734) 812-3884
43812 Leeann Lane
Canton, Michigan 48187
Written "By Ron Parko"