AC power plugs and sockets



AC power plugs and sockets connect electric equipment to the alternating current (AC) power supply in buildings and at other sites. Electrical plugs and sockets differ from one another in voltage and current rating, shape, size, and connector type. Different standard systems of plugs and sockets are used around the world.
Plugs and sockets for portable appliances became available in the 1880s, to replace connections to light sockets with wall-mounted outlets. A proliferation of types developed for both convenience and protection from electrical injury. Today there are about 20 types in common use around the world, and many obsolete socket types are found in older buildings.
Adapters between standards are not included in the standards, and as a result they have no formal quality criteria defined. Physical compatibility does not ensure that the appliance and socket match in frequency or voltage. Adaptors allow travellers to connect devices to foreign sockets, but do not change voltage or frequency. A voltage converter is required for electrical compatibility in places with a different voltage than the device is designed for. Mismatch in frequency between supply and appliances may still cause problems even at the correct voltage.
A lampholder plug fits into a light socket in place of a light bulb to connect appliances to lighting circuits. Where a lower rate was applied to electric power used for lighting circuits, lampholder plugs enabled the consumers to reduce their electricity costs. Lampholder plugs are rarely fused. Edison screw lampholder adaptors (for NEMA 1-15 plugs) are still commonly used in the Americas.
In Chile, 10 A Magic connectors are commonly used for computer/laboratory power networks, as well as for communications or data equipment. This allows delicate electronics equipment to be connected to an independent circuit breaker, usually including a surge protector or an uninterruptible power supply backup. The different style of plug makes it more difficult for office workers to connect computer equipment to a standard unprotected power line, or to overload the UPS by connecting other office appliances.
Snap and lock DC power connectors look similar to Mini-DIN connectors, but have either 3 or 4 thicker pins and a slightly larger mating shell. Because of this they do not mate with any of the standardized Mini-DIN connectors. Some devices, however, use a true 4-pin Mini-DIN connector for power instead, presenting the possibility to mate such a connector with the wrong port (such as an S-Video output).

Industrial and multiphase power plugs and sockets



Industrial and multiphase plugs and sockets provide a connection to the electrical mains rated at higher voltages and currents than household plugs and sockets. They are generally used in polyphase systems, with high currents, or when protection from environmental hazards is required. Industrial outlets may have weatherproof covers, waterproofing sleeves, or may be interlocked with a switch to prevent accidental disconnection of an energized plug. Some types of connectors are approved for hazardous areas such as coal mines or petrochemical plants, where flammable gas may be present.
Almost all three-phase power plugs have an earth (ground) connection, but may not have a neutral because three-phase loads such as motors do not need the neutral. Such plugs have only four prongs (earth, and the three phases). An example of a socket with neutral is the L21-30 (30 A) and the L21-20 (20 A) both of which have five pins (earth, neutral, and X, Y, Z phases).
Generally the plug is the movable connector attached to an electrically operated device's mains cable, and the socket is fixed on equipment or a building structure and connected to an energised electrical circuit. The plug has protruding pins or, in US terminology, blades (referred to as male) that fit into matching slots or holes (called female) in the sockets. A plug is defined in IEC 60050 as an accessory having pins designed to engage with the contacts of a socket-outlet, also incorporating means for the electrical connection and mechanical retention of flexible cables or cords, a plug does not contain components which modify the electrical output from the electrical input (except where a switch or fuse is provided as a means of disconnecting the output from input). In this article, the term 'plug' is used in the sense defined by IEC 60050. Sockets are designed to prevent exposure of bare energised contacts.
In Europe, the most common range of heavy commercial and industrial connectors are made to IEC 60309 (formerly IEC 309) and various standards based on it (including BS 4343 and BS EN 60309-2). These are often referred to in the UK as CEE industrial, CEEform or simply CEE plugs, or as "Commando connectors" (after the MK Commando brand name for these connectors).
In this industry the above-mentioned IEC 60309 connectors are referred to as CEEform (or just CEE) connectors. 230 V single-phase (blue) and 400 V three-phase (red) connectors between 16 A and 125 A ratings are used.
Where more current carrying capacity is required, such as between generator sets and distribution boards, VEAM Powerlocks or Cam-Loks may be used. These connectors are single pole so five are required to accommodate all three phases, neutral and ground. Powerlocks have a rating of 400 A or 660 A at 1 kV. Cam-Lok E1016 Series are rated at 600 V 400 A.
Where it is necessary to run separate feeds through multicable, the Socapex 19-pin connector is often encountered on theatre and studio lighting rigs.
The first stage pin connectors had two cylindrical pins, one for line (hot) and one for neutral, arranged symmetrically in a rectangular housing. The housing was milled from a solid block of fiberglass or bakelite which may have been impregnated with asbestos for fire resistance, with a screw-on cover. Later connectors (including those currently manufactured) use molded plastic or machined phenolic resin laminate housings .
All stage pin connectors have longitudinal slits in the male pins that allow for compression when inserted into the female sockets to increase friction and therefore the mechanical security of the connection. A special tool appropriately called a pin splitter may be used to expand this slit and spread the two halves of the pin to compensate for wear. A knife may be used to the same effect, but this technique risks both personal injury, damage to the connector, or ruining of the knife blade. For these reasons, a flat-head screwdriver is often used as an impromptu pin splitter.
Most extension cables made with 20 A stage pin connectors use 12/3 type SOOW or SJOOW cable which has three individually insulated 12 awg (American Wire Gauge) stranded conductors inside a larger jacket. The internal insulation is usually colored black (for line), white (for neutral) and green(for ground). This cable configuration can safely handle the full 20 ampere rating of the connector. The designation SOOW or SJOOW refers to the cable's insulation construction and type. SJó (300 volts, maximum) and Só (600 volts, maximum) are both "most severe" service cordage. This type of cable is very hard-wearing, resistant to oil and moisture, and resists the kinking that can result in internal conductors unlaying and twisting, which is a common problem with the SJTW cable often used in household-grade extension cords. However, older cable made using natural rubber is susceptible to dry-rotting, particularly with the heat generated by lighting equipment. This can cause the insulation to fail and expose or short circuit the conductors leading to shock or fire hazard if old cable is not inspected regularly and replaced as needed.