Electrical receptacles, outlets, and wall sockets accept plugs and provide current to run electrical devices. They are used in a variety of residential, general-purpose, commercial, industrial, laboratory, and hospital applications.

Types of Electrical Receptacles

Several blade or pin types are available.

Straight (non-locking) electrical receptacles are inserted at a right angle to the plane of the matching device face.

Locking receptacles fix or lock a plug in place when the plug is inserted and then rotated.

Pin and sleeve receptacles, plugs with round pin contacts, are inserted at a right angle to the plane of the receptacle face.

Specifications

Important specifications for electrical receptacles include number of wires, number of poles, and grounding method.

Electrical receptacles provide maximum voltage. Typically, devices are designed for either single-phase or three-phase power. Maximum voltage ratings for electrical receptacles include:

• 125 V
• 250 V
• 277 V
• 347 V
• 480 V
• 600 V

There are two maximum voltage ratings for 4-pole, 4-wire and 4-pole, 5-wire devices: 120/208 V and 277/480V. Voltage ratings for 3-pole, 4-wire electrical devices include 125/250 V. Voltage ratings for 4-pole, 5-wire devices include 347/600 V.

Electrical receptacles are available with a variety of maximum current ratings, including 15, 20, 30, 50, 60, and 100 A. International current ratings include 16, 32, and 125 A. Most homes in the U.S are wired with a combination of 15-amp and 20-amp circuits. A 14-gauge wire is used to serve a 15-amp circuit and a 12-gauge wire is used for 20-amps. Also, 20-amp circuits are protected by a breaker or fuse. The easiest way to determine whether the circuit is 15 or 20 amps is to look at the corresponding breaker or fuse in the breaker panel.

Number of Wires

Wires transfer the power between devices. In general, a single phase volt system will have two wires if only the lower voltage is available. One wire is for the phase and the other is neutral. If higher and lower voltages are available, the power plug will have three wires; Two phase wires and the neutral. Electrical receptacles with between one and five wires are commonly available.

Configuration

The configuration of the device determines how many receptacles it has for the power connector. There are several options available.

Single- The device only has one receptacle.

Duplex- This configuration is the most commonly seen in housing and commercial industries. They have two receptacles.

Triplex- This configuration is also commonly seen in housing and commercial industries. They have receptacles to accept three plugs.

Quad or four-in-one- This device provide a way to add multiple receptacles in a common housing. It mounts as a single unit.

Four-in-one configuration. Image Credit: Leviton 

Number of Poles

Poles control one path of the circuit. A pole is an outlet terminal for a switching device, a combination of mating contacts, or both. Typically, electrical receptacles have between one and five poles.

Grounding Method

The grounding method determines the path that electricity follows when moving from a defective receptacle back into the earth. There are different grounding options available based on the needs of the system. These include,

Non-grounding connectors do not have a ground option.

Standard grounding devices have a standard embedded ground terminal

Isolated grounding devices use a ground path that is isolated from the facility's grounding systems. This increases the resistance of sensitive electronics to surges. They also provide a clear grounding path to the service panel and help reduce electromagnetic noise that can interfere with equipment operation.

Self-grounding connectors establish a connection to en existing grounding path such as a metal wiring device or metal conduit, gas or water pipe, or ducting or structural steel.

Ground fault circuit interrupter (GFCI) connectors include a built-in circuit that detects leakage current to ground on the load side of the device. When leakage current is detected, GFCI interrupts power and prevents hazardous ground fault conditions. National Electric Code NFPA-70 requires GFCI use in many indoor and outdoor locations.

GFIC receptacle. Image Credit: Leviton 

Mounting

There are several mounting styles for electrical receptacles.

Standard DIN rail or fit the ends of electrical cables. They can also be equipped with integral mounting hardware

Panel mounted devices fit a depression within a panel so that they are flush or nearly flush with the surface.

Flange mounted devices attach by bolting the flange or riveting it in place through holes in the flange surface.

Wall or box mounted electrical receptacles include an accessory such as a back shell for permanent mountings.

Through hole technology (THT) mounts electrical receptacles on a printed circuit board (PCB) by inserting component leads through holes in the board and then soldering the leads in place on the opposite side of the board.

Surface mount technology (SMT) adds components to a printed circuit board (PCB) by soldering component leads or terminals to the top surface of the board. Typically, the PCB pad is coated with a paste-like formulation of solder and flux. With careful placement, SMT components on solder paste remain in position until elevated temperatures, usually from an infrared oven, melt the paste and solder the component leads to the PCB pads.

Features

Electrical Receptacles have several features available that may be beneficial for user application.

Corrosion resistant- Corrosion resistant devices are made of special materials and/or plated metal parts that are designed to withstand corrosive environments. Corrosion resistant devices must pass the ASTM B117-13 five-hundred hours Salt Spray (Fog) Test with no visible corrosion. 

Dust proof- Receptacles are designed so that dust will not interfere with their operation. The IP suitability rating describes the degree of protection that a device offers against the ingress of foreign objects (e.g., IP 20). 

Power light- Electrical receptacles include a power light to indicate if they are live. The receptacle may also be illuminated to make connection easier in dim or dark work spaces. 

Tamper resistant- Devices are constructed so that access to their energized contacts is limited. Tamper resistant receptacles are required by the National Electric Code NFPA-70 in specific pediatric care areas in health care facilities.

Watertight- Receptacles are constructed so that water cannot enter under specified test conditions. The IP Suitability Rating designates the degree of protection a device offers against the ingress of moisture and water (e.g., IP-55, IP-44). Some devices may also be approved for moisture resistant, and under water applications.

Integral surge protection- Devices include integral surge protection against mild to moderate spikes or peaks in electrical supply.

Rotating outlets- The outlet can be position to accommodate larger plugs.

Electrical receptacles can also come in a variety of colors and decorative designs to match the aesthetics of the building.

Applications

Electrical Receptacles are used for specific types of instruments, equipment, machinery, and computers. Some electrical connectors are designed for use in hazardous environments or marine environments. Electrical receptacles are used in almost every industry including residential, commercial, industrial, and medical facilities.

Standards

Electrical receptacles are designed to meet requirements from the following organizations:

• National Electrical Manufacturers Association (NEMA) sets standards for electrical cabling and connectors.  
• The International Electrotechnical Commission (IEC)  is a worldwide body responsible for developing consensus global standards in the electrotechnical field.  
• Consortium for Energy Efficiency (CEE) is a European organization for electrical standards.  
• Japanese Industrial Standards (JIS) is a Japanese organization for electrical standards.

There are many organizations across the world that determine and maintain electrical standards to ensure safe and efficient use of power plugs. Engineering360 allows users to search by country to ensure they select a power connector that can be safely incorporated into their system. 

Resources

Electric Current Worldwide

Power Connector Tutorial

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AutomationDirect