Plastic electrical box (C) D FriedmanElectrical Box Type & Size FAQs
Q&A on electrical boxes for receptacles (wall plugs or "outlets")

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Guide to types of electrical receptacles (wall "outlets" or "wall plugs"):

How to choose the right type of electrical receptacle when adding or replacing a wall outlet in a building. Here we describe matching 15-Amp receptacles to 15-Amp circuits, 20-Amp receptacles to 20-Amp circuits, two-wire receptacles where no ground is present, GFCI and AFCI electrical receptacles, and the proper electrical box to hold and mount these devices.

This article series describes how to choose, locate, and wire an electrical receptacle in a home. Electrical receptacles (also called electrical outlets or "plugs" or "sockets") are simple devices that are easy to install, but there are details to get right if you want to be safe.

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Choose the Proper Electrical Junction Box When Adding a Receptacle

Arcing in an under-sized electrical box (C) Carson Dunlop Associates

The proper sized and type of junction box must be used to house the electrical receptacle, must be properly secured in the wall, and must be located at the proper height from the floor.

Recently-posted questions and answers about electrical box types

The National Electrical Code Article 314 contains complete details and tables of electrical box sizes in dimensions and cubic inches and should be consulted for complete accuracy because the actual size of the box required, in cubic inches, depends on the number of wires that will be within that enclosure.

On 2017-02-28 01:58:59.929719 by (mod) - using box extensions for recessed boxes


I like using box extensions - of which 1/4" thick is a standard dimension - along with screws of sufficient length, because it
- gives a stronger mount for the device and the face plate
- for deeper-recessed boxes I'm confident that the box is totally enclosed - no openings into the wall cavity around the box.

On 2017-02-28 00:16:41.047952 by john

all the switch and outlet boxes in the home we are having built are 1/4"+ recessed into the drywall. will box extensions be necessary or will they be ok using longer screws. great website

On 2017-02-09 00:42:41.862827 by steve carver

should have added to be mounted in attic with blank, also they are allied boxs there is i think

On 2017-02-09 00:34:51.632598 by steve carver

can you use 3 and 4 gang device boxes as junction boxes..purpose is for more volumn

On 2017-01-02 22:32:23.322466 by Anonymous

How to install a standard electrical box in a six inch diameter hole

On 2016-12-08 17:26:00.286283 by (mod)


There are receptacle mounting covers that will fit on a round electrical box, but before you go that route you need to look at the box size (diameter and depth and cubic inches) to be sure that there is adequate and code-complying wiring space.

In a companion article you'll see an example of a fairly deep round electrical box being reinserted into a ceiling and secured to support the weight of the light fixture. That could have been a receptacle instead.

If the receptacle ears that mount to the box don't fit the existing screw receives on the round ceiling box you 'll need to purchase an adaptor plate that mounts to the existing box screws and contains additional screw fittings and a cutout to which the receptacle is mounted. Then there are some nice round receptacle covers such as the brass ones from Raco, Carlon, Gampak and Reddot also make a round box cover for exterior fixtures that could work. Look at your electrical supplier or at a building supplier like Lowes or Home Depot or your local hardware store.

On 2016-12-08 17:12:04.597300 by Convert ceiling light receptacle

I would like to install a electrical single gang outlet in my ceiling where we currently have an empty plastic round electrical box that has all the wires available. Do they sell kits that have the outlet and outlet cover that will fit into the round box or will I need to purchase a single receptacle and then try to find a single receptacle outlet cover (which is not easy to find).

On 2016-11-19 22:20:25.839710 by (mod)

Sorry, Birge I don't know what black box you are asking about.

On 2016-11-19 20:18:34.117269 by Birge

Can an open back box be used for 120 V circuit?

On 2016-11-10 20:05:19.092746 by (mod)

Gabriel I think the answer is ... it depends. E.g. in NYC wiring is armored cable and thus of course metal junction boxes.

On 2016-11-09 23:02:21.924275 by Gabriel

In commercial applications. Does the ceiling box need to be meta? what is the minimum size required? 3"? or 4"?

On 2016-10-17 19:58:39.143934 by Michael

Is there a weight requirement for ceiling boxes in commercial buildings. An is there a difference between a metal box an a plastic box for the ceiling

On 2016-09-29 23:56:23.348147 by (mod)

SS covers are unsafe. Relying on a ground plug prong to avoid sparks isn 't avoiding somebody getting fried. I'd suggest a better grade of receptacle and a heavier plastic cover.

On 2016-09-29 20:37:24.544197 by Anonymous

We install outlets with the ground plug up. We use the outlets heavily and have SS covers. When they get loose they sometimes fall onto the hot and neutral causing a show. Ground plug on top solves the issue.

On 2016-05-30 22:49:19.070116 by (mod)

Paul, I agree that some old boxes are waay too small to jam in a new GFCI receptacle. Even taping the sides to avoid electrical contact is unsafe, improper, and doesn't solve the over-crowded box problem.

Yes the best solution is to install a larger box and wall plate.

On 2016-05-30 22:48:22.285041 by (mod)


REplace the box

On 2016-05-21 16:46:56.216556 by Paul

I tried to install a g f i in a standard wall box but the side clearance is almost against the box. Can I get a wall box about 1/4 in. id.wider so that the cover plate will fit

On 2016-05-19 01:32:31.149301 by Al

I have a 3 1/2" round outlet box in the ceiling of my garage. How do I make a standard outlet fit into it?

On 2016-04-03 03:21:34.043689 by (mod)


This common problem can be easily fixed, Hank.

Stop by your local electrical supplier, or building suppliers such as Home Depot, and look through the plastic electrical box extenders.

These are plastic rectangles sold in various thicknesses that serve essentially as a rectangular but structural washer to bring the face of the electrical box out flush with the surface of the wall.

Typically you can buy an electrical box extender of sufficient thickness to do the job, or you might need to buy a pair of them depending on the thickness of your drywall.

Plastic electrical box extenders are also discussed at this website.

On 2016-04-03 02:29:57.107680 by hank

Kitchen remodel electrician used metal clad cable and metal boxes -- at our request -- but installed the boxes flush with the studs. Now they're more than half an inch below 5/8 sheetrock. They're licensed electricians, but young.

Am I being fuddyduddy about wanting the boxes brought forward with metal extenders here? Hell, I always installed the temporarys with screws so I could back the screws out and pull the box forward as needed.

So what if there's "nothing in the electrical box that can burn" -- which I don't believe anyhow. I can't see leaving a gap between the front of the metal box and the back of the sheetrock as being safe.

Someone point me to a code cite for the exact rule?

And that was with a manual screwdriver, uphill both ways in the wintertime.

They got power screwdrivers.

On 2016-02-08 17:19:15.033623 by (mod)

Floor receptacles, if permitted by your local electrical inspector, require a special cover designed for floor-use and intended to protect the receptacle from dirt, water, damage. Typically they're brass or stainless steel, flush with the floor surface. The box can be plastic or steel as permitted locally.

On 2016-02-08 16:49:25.639627 by Wayne Hadley

Hello! I am thinking of putting a plug in the floor, under my kitchen table. The floor is ceramic tile. Could you please tell me what codes I need to know about. On the box, plastic and steel ?? Thank You

On 2015-11-05 20:36:36.598516 by (mod)

Robert we've provided a detailed reply along with a repeat of your question in a companion article at


On 2015-11-05 06:43:32.958992 by ROBERT WEISBERG


On 2015-09-10 13:57:58.805003 by (mod)

Mark there are quite shallow steel electrical boxes - about 3/4" deep - available at electrical supply houses.

On 2015-09-10 10:56:11.325924 by Mark

Does any company make a smaller (depth) interior electrical box, that houses the plugs and switches behind the drywall. We are installing on the outside of a cabinet and are pressed for depth space.


On 2015-07-21 09:43:53.327760 by Robert

can a single ground wire be added to a two wire system

On 2015-04-10 16:40:48.753180 by (mod)

I may be missing something Anon but certainly 3-way switches are widely available from electrical suppliers and home supply stores; to go to mroe than 3-way one uses the same switch type.

On 2015-03-28 17:10:56.561430 by Anonymous

I seem to have a 3 inch box for two toggle switches, a 3 way and a 4 way. Would like to replace them with more up to date switches but am unable to locate any.

On 2014-08-06 21:38:41.491250 by Dick N


What I meant was: Is it legal to use a plastic outlet box with AC or MC cable when there is only one cable entry and therefore no issue of bonding the cladding of multiple cables together?
How about when there is a second cable entry but that one is non-metalic?

On 2014-08-06 16:34:01.207360 by Dick N

Is it legal to use a plastic box with AC or MC cable?

Question: I'm installing a box extension but the top screw won't hold - it's stripped

I started installing a box-extender on a receptacle in my kitchen because I'm tiling my backsplash and need to raise the outlet above the tile. However, the top screw connecting the outlet and box wouldn't hold. I spent way too much time bent double under my cabinets trying to get it to bite, but when I finally gave up and pulled it out it was stripped at the tip (which was as far as it'd go in). I'm sorry to bother you with triviality, but I'm new to home renovations and don't know what to do. Advice? - Julia 1/29/13

Reply: step by step tips for replacing a stripped electrical receptacle or switch box mounting screw or screw opening


If the problem is the screw itself is stripped, simply purchase a replacement screw or a hand full of them from your electrical supplier. These screws are a standard thread and length, but longer versions are available at any hardware store.

For the case you describe, if the stripped problem is the mounting hole you'll need to either enlarge and tap the hole for tine next size larger screw, or purchase a clip-on adapter that slips over the stripped ear through which the original hole passed.

Taking care to move electrical wires out of the way of your drill bit, in a metal electrical box you can drill out the 6/32 screw opening to tap and accept an 8/32 screw.

For photos and step by step details on how to repair stripped electrical outlet mounting screws, see OUTLET BOX SCREW REPAIR.

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