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Introduction to Ceiling and Wall Electrical Boxes

Lighting, Ceiling Fan and Junction Boxes

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Electrical boxes are a critically important component of your home's electrical system.However the variety of boxes can seem confusing when you're planning your project. Sothis tutorial will describe the different types of electrical boxes you find in the ceiling and

wall for lighting, ceiling fans and junction boxes.

There are varieties for plastic and metal boxes, new work and old work boxes, round,square and octagonal boxes. And they come in depths ranging from 1/2" to over 3" deep.Then there are boxes with no backs that serve as depth extenders and covers with cutoutsfor various uses!

Well, after reading this tutorial you will understand why there are different box types andin what applications they may be used.

Electrical wall and ceiling boxes can be used in many ways, such as: 

  Join or splice wires together in circuits

  Mount and house connections for a lamp fixture to a wall or ceiling

  Mount and house connections for a ceiling fan (when rated for this use andappropriately braced or mounted)

  Mount recessed in a wall or ceiling or surface mounted  Wired using non-metallic electrical cable or metallic conduit and wire applications.

Let's take a look now at the various types of electrical boxes and their features and uses.

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Metal and Plastic Electrical Boxes

Example of Metal and Plastic Electrical Box

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Throughout this tutorial you will see examples of metal boxes and plastic boxes. If you areusing metal conduit to run wiring to the electrical box, then a metal box is requiredbecause the conduit and metal box system itself may be used to ground the system. If you

are using non-metallic wiring Type NM-B (nonmetallic-sheathed cable) which is typicallyfound in residential applications as branch circuits for outlets, switches, lighting and so on,then you can use either plastic boxes or metal boxes as long as the cable is secured to thebox. With NM-B, grounding occurs with a dedicated wire made part of the cable.

Type NM-B electrical cable is the most common way to wire a home and you may hear itreferred to generically as Romex®. However Romex® is a brand name of  Southwire Co. for NM cable just as Kleenex® is often used to describe facial tissue.

Metal boxes come in types known as:

  Drawn Steel (1 piece construction);

  Interlocked / Gangable (typically for switch and outlet boxes).

Plastic boxes can be made from different types of molded plastic and are always 1 piececonstruction. They can be made from:

  PVC (most common);

  Phenolic Resin;

  Fiberglass.

Now let's take a look at the various types of ceiling and wall electrical boxes you

find in the home. 

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Round Pan Electrical Box

1/2" Deep Round Pan Box

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ROUND PAN ELECTRICAL BOX 

Typical Size:1/2" and 3/4" Deep; 3-1/2" Round

Usage:

  Metal box typically used for installation of ceiling or wall mounted light fixtures up to 50

pounds.

  Plastic box may used for outlet mounting.

  Some types of specially rated metal pan boxes may be used for mounting ceiling

fans but not all pan boxes may be used for this purpose. (See Ceiling Fan Rated Boxes section)

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Octagon and Round Electrical Box

Octagonal and Round Electrical Boxes

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OCTAGON AND ROUND ELECTRICAL BOX 

Typical Size:1-1/2" to 2-1/8” Deep 

Usage:

  Typically used for installation of ceiling or wall mounted light fixtures up to 50 pounds;

  May be used as a Junction box;

  Metal box may also be used as a switch or outlet box in surface mounted installationsusing metal conduit;

  Round plastic box usually has "ears" for fastening to wall or ceiling in existing or "oldwork" applications.

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Ceiling Fan Rated Electrical Box

Ceiling Fan Boxes Require Special Rating and Design

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CEILING FAN RATED ELECTRICAL BOX 

Typical Size:1/2" to 2-1/8” Deep 

Usage:

  Must be rated for ceiling fan mounting by UL in a UL-listed electrical box marked “ForUse With Ceiling Fans.”  

  May be a round or octagon shaped UL Listed box;

  Requires special fastening due to dynamic loading of rotating fan;

  Depending on assembly, may accommodate installation of ceiling fan and light fixtureup to 75 pounds or more;

  May be mounted directly (with 4 screws) to ceiling joist, wood blocking or may attach toadjustable brace spanning between ceiling joists.

Application: For a great overview of installing a ceiling fan see this article called Remote ControlledCeiling Fans. written by Elizabeth Weintraub, About.com's Guide to Home Buying/Selling.

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 4" Square Box

Square Boxes Provide Maximum Volume for Multiple Conductors and Connectors

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4" SQUARE BOX 

Typical Size:1-1/4"- 2-1/8" Deep

Usage:

  Square boxes provide maximum volume for multiple conductors and connectors;

  Most often square boxes are used to run multiple conductors in two or more directions

to bring power to various electrical devices. (See Junction Boxes); 

  Square boxes may also be installed in ceilings or walls for lighting fixtures, switches orreceptacles.

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Square, Octagon and Round Box Covers

Different Covers Provide Multiple Use Opportunities

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SQUARE, OCTAGON AND ROUND BOX COVERS 

Usage:

  Covers are used to close an outlet box and are required by code. Never leave a box

uncovered.

  Switches or receptacles may be installed into square or octagon boxes by using covers

with cutouts;  Octagon or round covers are used for mounting light fixtures;

  Raised 4” square covers are used for mounting switches or receptacles; 

  Flat round closure plates (5”) are designed for use in dry locations to close unusedceiling outlets.

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Junction Box

Junction Boxes are Typically Square Boxes

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JUNCTION BOX 

Typical Size:4" Square; 1-1/4"- 2-1/8" Deep

Usage:

  A  junction box is an electrical box used to run multiple conductors in two or moredirections to bring power to various electrical devices.

  Junction boxes are required to be installed so they are always accessible;

  Never install a junction box in a concealed wall or ceiling space where is can not beaccessed in the future.

  Wire connectors (wire nuts) and wire lengths take up a lot of space in a box. Becausesquare boxes provide maximum volume for multiple conductors and connectors theyare most often used as a junction box.

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Box Extenders: Adding Capacity 

Box Extenders Add Wiring Capacity to a Box

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BOX EXTENDERS: ADDING CAPACITY 

Usage:

  Extension rings or box extenders are those funny looking square or octagonal boxes

that have no back on them.

  Extenders are designed to bolt onto the base electrical box and provide additional cubic

inch box capacity for wiring and connectors.

Advantages and Disadvantages of Plastic Electrical Boxes 

Plastic junction boxes have their advantages and disadvantages. Although they are easy toinstall, they are not always the best choice for every application.

Advantages 

In electrical installations, electrical boxes are used to install electrical devices, make

splices and install light fixtures. This leads to a choice of types of boxes, plastic or metalboxes. Plastic boxes are nonconductive and easy enough to install. They have two nails,both on one side of the box, that allow the box to be fastened to the studs in your home.Plastic boxes have markings on the side that show different depths that the box can be setout to allow flush alignment with the outer wall of drywall or wall surface. This allows theoutlet, switch, or light fixture to sit flush against the box opening and the wall face forproper alignment and installation.

Disadvantages 

Plastic boxes have their disadvantages also. Along with the box being plastic, the nail

brackets are also plastic. They are easily broken off when installing a box or when you

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have to take a box off and reinstall one. Once this bracket clip is damaged or broken off,your mounting options are all but gone.

One look at the face opening of the box and you’ll notice there are two screw holes thatmake it possible to install a switch, outlet, or other device to the box. As with anythingplastic, the threads inside the mounting holes are threaded and they are easily stripped if the screws are not installed properly.

Quite often, you may be tempted to put any old screw into these holes, but the threadsare usually set to a 6-32 thread. In the event the threads do become stripped, you may beable to still use the box by installing a short drywall screw into the hole, that is, if it isn’tcracked or damaged. We want the screw to firmly hold the device

in place so that it doesn’t short out. 

As for mounting light fixtures and ceiling fans, I recommend usingmetal boxes. Although there are some plastic boxes that aredesigned to support these fixtures, I personally have little faith inthe plastic threads that support a fixture over my head. And whilewe are discussing that matter, keep in mind to use the specially

designed light fixture and fan mounting boxes that come completewith mounting brackets. These setups are specifically designed tohandle the weight that some of these lights and fans have.

Plastic Electrical Box Uses

What Are Plastic Electrical Boxes?

Plastic electrical boxes have their pluses and minuses. Because they are plastic, there is noneed to attach a ground wire to it. Since it is made of a non-conductive material, switchesand outlets cannot short out if they touch the side of the box.

Plastic boxes usually come with tapped screw holes for easy attachment of switches andoutlets. These boxes come in a single-gang, double-gang, and even multiple-gangconfigurations.

You can choose between plastic boxes with nail-on brackets, complete with nails, or a cut-in version that has tabs that spin out when tightened to hold the box securely to the wall.

The disadvantages of plastic boxes are their brittleness and wire support brackets. Let meexplain. If you look at the box, you'll notice that the device screw holes are also plastic. If 

the screw is lined up when installing the device, you're fine. But get the screw cross-threaded and you have a problem. Suddenly the screw won't tighten down and the deviceis flopping in the wind. If the metal hole in a metal box strips out, you can just tap it outand it's as good as new. Not so easy with a plastic box.

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The same holds true for the nail-on mountingbrackets. If you hammer the nails carefully and don'taccidentally hit the plastic bracket, you're fine. But theslightest miscue of the hammer head on the plastic

bracket or body and the box is toast. Metal boxes can take apounding and still function.

The plastic boxes sometimes have plastic push-in tabs to hold the nonmetallic sheathed(NM) wire. These tabs serve their purpose I suppose, but I'd much rather have a wireconnector or a metal clamp with a screw that I can tighten the tension to hold the wires inplace. In this case however, this box has knockouts to remove with no fastener for thewires.

One more thing I'll say about plastic boxes is that if you have a choice between a plastic ormetal box, I would definitely choose the metal box every time. Yes, I suppose the plasticboxes are cheaper and easier to put up, but after years of experience, I'd still choosequality over price. My metal box will survive a fire, will your plastic box?