Electrical receptacle (C) Daniel FriedmanElectrical Receptacle Types
Buyer's Guide to electrical receptacles (wall plug or "outlet")

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Types of electrical receptacles: how to select the right type of electrical receptacle (outlet):

It's important to use 20-A rated receptacles if the electrical circuit is a 20-amp circuit. Don't install a grounded electrical receptacle plug on a circuit that has no electrical ground. Remember to install AFCI or GFCI devices where they are required.

This article explains how to match the receptacle type to the circuit type and use. We describe both 120V receptacles and 240V receptacles.

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.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Choose the Proper Electrical Receptacle Type

Types of electrical receptacles (C) Carson Dunlop Associates

The proper type of electrical receptacle must be selected: some receptacles are rated only for 15-Amp circuits and must not be installed on a 20-Amp circuit.

20-Amp electrical receptacles may be designed to only accept plugs for 20-Amp appliances (which may have a different plug-spade configuration in which one of the plug terminals is twisted to be at 90 degrees to the other).

[Click to enlarge any image]

Some 20-Amp electrical receptacles are designed to accept either conventional plugs used by a 15-A appliance as well as 20-A plugs used by a 20-A appliance.

It's generally ok to plug a 15-A appliance into a 20-A circuit since that appliance is not going to overload the circuit in normal use. But the opposite is not true

. If you plug a 20-Amp appliance into a 15-Amp circuit you are risking overloading the circuit and tripping the circuit breaker, blowing the fuse, or worse, overheating the circuit and risking a fire.

Below our photographs illustrate a 15-Amp grounded electrical (below left) and a 20-Amp grounded electrical receptacle (below right).

You'll notice that the heavier-duty 20-Amp electrical receptacle has that T-slot at it's wider connection opening - an easy way to identify a wall receptacle rated for 20-Amps - provided that the receptacle was properly matched to the wire size and the circuit breaker or fuse size.

15 Amp Electrical receptacle (C) Daniel Friedman 20 Amp Electrical receptacle (C) Daniel Friedman

Details about how to wire up an electrical receptacle are at ELECTRICAL RECEPTACLE CONNECTION DETAILS - where to connect black, white, red, green, ground wires .

Two-Wire Electrical Receptacle Circuits

Comparing grounded and un-grounded electrical receptacles © D Friedman at

Older two-wire electrical circuits, such as the two circuits depicted at the right of our sketch above may provide only the hot and neutral wires and no ground wire.

If no ground wire or ground path is provided, it is improper and unsafe to install a grounding (3-prong) electrical receptacle on that circuit.

Color coding of wires to properly connect an electrical outlet (C) Carson Dunlop AssociatesOur photo (above left) shows a conventional grounded three-prong electrical receptacle - the round hole is the ground connection - at the left end of the picture closest to my thumb.

At right in the photo is an ungrounded electrical receptacle. This is the right device to install if no ground is present on the electrical circuit.

You don't want to "fool" a building occupant into thinking that a ground is present when there is not one, so you don't install a receptacle that has that third ground opening in its face.

Some older two-wire circuits which are covered with a flexible metal jacket ("BX" or "armored cable" wire) may provide a ground path by means of the cable jacket itself.

We don't rely on it, and in event of certain short circuits it's unsafe: the exposed metal sheathing of the wire becomes live, risking a shock.

Details about how to wire up an un-grounded receptacle are at CONNECTION for 2-WIRE RECEPTACLE CIRCUITS - no ground

The illustration at above-left shows the typical wiring of an electrical outlet or "receptacle", courtesy of Carson Dunlop Associates.

Click any image to see an enlarged, detailed view of electrical wiring details for "plugs" or electrical receptacles.

Choosing GFCI and AFCI Receptacles

GFCI outlet being tested (C) Daniel Friedman

Ground fault protection - GFCI's: The NEC also requires that only special ground fault circuit interrupter (GFCI) protected outlets can be installed in certain hazardous locations like kitchens, baths, garages, outdoors.

A GFCI-protected electrical receptacle includes circuitry that turns the electric power off at the outlet quickly should a ground-fault (electricity flowing to earth, such as through your hand and down a water pipe) be detected. [4]

AFCI device image from the US CPSC

Arc fault protection - AFCI's: Beginning in 2002 the NEC also required arc fault protection for electrical outlets for bedrooms. [4]

AFCI's are similar to GFCI's discussed above, but they include an additional level of protection against fire by detecting small electrical arcing at a connection - a condition that can lead to overheating and fire.

As you can see from this US CPSC photo, you can add Arc fault protection to a home circuit by installing a special circuit breaker in the electrical panel.

By this means you can provide arc fault protection and thus improved fire safety for all electrical outlets on the circuit - for example in the building's bedrooms

In the FAQs (below) we discuss the importance of wiring the Line and Load terminals of GFCIs and AFCIs correctly.


and AFCIs ARC FAULT CIRCUIT INTERRUPTERS for details about these devices.

Readers of this article should also see SAFETY for ELECTRICAL INSPECTORS.

This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions.

Question: Is it safe to plug a 10-Amp A/C into an outlet that is back wired?

is it safe to plug in an ac unit that runs 10 amps , into outlet that is backed wired, i had read that you don't like this method, the outlet is on third floor and is on a 15 amp breaker - Johnny B 5/2/12

Reply: Comparing Three Types of Backwired Receptacles: 20-A Clamp Type & 15-ASpring Type & Clamp Type Backwiring Devices

Receptacle 20A backwired clamp type © D Friedman at Johnny, that's an interesting question and one I'm scared to answer - by online posting one cannot assure the electrical safety of your building.

Details about back-wired electrical devices (receptacles & switches) are at BACK-WIRED ELECTRICAL DEVICES.

Here we will illustrate three different types of electrical receptacles that can be wired from their back-side.

Our photo (left) illustrates a spec-grade 20-Amp, 125V rated electrical receptacle that looks as if it is "back-wired" - in fact while a wire can be wrapped around the terminal screws on this device.

The screw is intended to be used to tighten a rectangular brass plate against a square metal nut (silver in color) that makes a very strong and positive connection over a good area of wire surface.

This receptacle is marked on its back surface as CU Wire Only - copper only. [Click images to see enlarged details.]

That said, I agree that older, spring-type back-wired electrical connections (shown at below left) are not as reliable as connections made under a screw or clamp, as the total contact area between the back-wire spring edge and the wire surface is minimal.

Nevertheless, on a 15-A circuit using 15-A devices such as receptacles, the circuit and its devices are rated and intended to be able to support the 10-amp load you describe, so long as the sum of all of the items plugged into that electrical circuit don't overload it.

Contractor-grade 15-A spring-type-connector back-wired electrical receptacles (below left) provide a single opening at each of the four terminals (two neutral wires, two hot wires) on the back of the receptacle (red arrow).

The yellow arrow points to a release spring that will allow removal of the wire, but we prefer not to re-use this type of back-wired receptacle. Tightening the screw at the main wire terminal (blue arrow) has nothing to do with the spring-clamp that is securing the back-wired terminal wire.

Back wired electrical receptacle (C) Daniel Friedman Back wired electrical receptacle (C) Daniel Friedman

Some newer heavy-duty 15-A back-wired electrical receptacles (above right) o not rely on a simple spring-edge to contact the electrical wire, as we illustrate in our second photo (above right).

Rather, when the wire is inserted into a receiving hole on the back of the receptacle (either of the two red arrows).

When the terminal screw is tightened (blue arrow) that actually snugs up a clamp that contacts a much larger surface area of the back-wired wire.

That's a more secure connection mechanically. On this receptacle, instead on a single back terminal accepting a single wire, there are a pair of back terminal openings at each of the four terminal screws.


Thank you for responding, my town home was built in 1999, not sure if that is considered newer or older, lights do dim though when i use 10 amp vacuum . - Johnny B.


Backwiring electrical receptacles is a permitted installation and might be found in a 1999 home - but as we show above, there are two different approaches, the second of which is a better quality installation and is in our opinion more reliable.

Older & Antique Electrical Receptacles or "Outlets"

Un-grounded electrical receptacle (C) Daniel Friedman

At above and below are photos of an un-grounded electrical receptacle found in many older homes where the electrical circuit wiring did not include a grounding conductor.

Surface mount 20A wall receptacle or "outlet" in Raleigh NC (C) 2015 InspectApedia Steve Smallman, Property Inspector

These receptacles can still be purchased and are the only receptacle type that should be installed on an un-grounded electrical receptacle circuit as the absence of a third ground-prong opening makes clear to the user that no ground is present.

See FALSE GROUND at RECEPTACLES for a discussion of how this particular receptacle enjoyed giving the author a shock.

Above at right is an antique surface-mount plastic or bakelite wall receptacle or "wall plug" or "wall outlet" in common parlance. This installation is not just obsolete but improper and unsafe as you can see exposed wires poking through the wall trim below the receptacle. Property inspector Steve Smallman, Raleigh NC, who contributed this receptacle points out that

Thanks to frequent InspectApedia contributor also cited at ABOUT

Below are two versions of another antiquated and complex electrical receptacle.

I think that these electrical receptacles provide either 120V or 240V connections depending on the receptacle and slots used and on the actual wiring present. Comments are invited.

Antique 4-slot electrical receptacle (C) Daniel Friedman

Below: an older Harvey Hubbell (1857-1927) design electrical receptacle designed to accept 120VAC wall plugs sporting either the "modern" 15A standard parallel blade design OR the older tandem design.

Hubbell, a prolific inventor of electrical receptacles, plugs, and also bulb sockets and controls, designed and patented a number of key electrical receptacles that are cited below.

Antique 4-slot electrical receptacle (C) Daniel Friedman

Below: illustration from Harvey Hubbell's Separable Attachment Plug patent from 1904.

Hubbell plug patent 774,250  in 1904 - at

[Click to enlarge any image]

Hubbell round pin floor receptacle (C) Bay State Home Inspections

Photo above: a round pin receptacle, possibly with ground and missing one mounting screw, possibly an early Hubbell-design round two-pin floor receptacle, courtesy of Bay State Home Inspections and discussed originally

This receptacle is also similar to George Thomas' receptacle and plug design from 1910 and cited below.


Below: an excerpt from the patent illustration for Harvey Hubbell's multiple attachment plug patent issued in 1904.

Hubbell US Patent No. 776,326 attachment plug patent disclosure (C)

Knife blade (flat) plug and receptacle connectors designed by Hubbell were produced as early as 1904 and became the dominant connector design used in the U.S. and Canada.

Thomas electrical plug in receptacle patent  952,961 from 1910 - at

240VAC Electrical Receptacles

20 Amp 240 Volt electrical receptacle typically used for smaller room or window AC units (C) There are several common appliances or tools that require a 240-Volt-AC electrical receptacle and a number of 240VAC (or 220 VAC or 204VAC depending on where you live) electrical receptacle designs.

When wiring a 240V receptacle the circuit wires used will include

No neutral wire is typically connected to this device. The 240V power is achieved across the two individual 120V "hot" circuits.

Examples are listed below.

Our photo of a 240V electrical receptacle shown here is a 20-Amp 240-volt electrical outlet that would be installed on a 20-Amp wall or window air conditioner circuit in a building.

This particular recetpacle, a Leviton product, is UL-listed for 20 Amp, 250 Volt, NEMA 6-20R, 2-pole, 3-wire circutis; it's further described as a narrow-body single receptacle, straight blade, commercial grade, grounding, side-wired, steel strap; available in ivory, white, brown. Similar products are sold in North America by Cooper, Eagle Wiring, and Pass & Seymour.

240-Volt window or through-wall room air conditioner

240-Volt equipment such as small welders

Below are two additional configurations and types of 240 VAC electrical receptacles.

The white three-bladed 240-V receptacle below is a 20-Amp Leviton product that is a non-grounding type electrical receptacle. This is a 20A, 125/250 V, NEMA 10-20R, 2P, 3W, narrow-body single receptacle, straight bladeed, non-grounding, side-wired, steel strap device.

240 volt electrical outlet or receptacle at

The orange 240 V receptacle below is a also a Leviton product, a flush-mounting twistlock single 20-Amp receptacle wired to provide an isolated ground and is described as a 20-A, 250V, NEMA L6-20R, 2P, 3W, flush mount locking receptacle, industrial grade with locking ground.

240 volt electrical outlet or receptacle at


Continue reading at BACK-WIRED ELECTRICAL DEVICES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES.


Or see GFCI PROTECTION, GFCI CODES - ground-fault-circuit-interruptor receptacles (and circuit breakers)

Suggested citation for this web page

ELECTRICAL RECEPTACLE TYPES at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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