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 3P+N+E which have five pins (earth, neutral, and X, Y, Z phases).

While some forms of power plugs and sockets are set by international standards, countries may have their own different standards and regulations. For example, the colour-coding of wires may not be the same as for small mains plugs.

Concepts and terminology

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.

To reduce the risk of users accidentally touching energized conductors and thereby experiencing electric shock, plug and socket systems often incorporate safety features in addition to the recessed slots or holes of the energized socket. These may include plugs with insulated sleeves, recessed sockets, sockets with blocking shutters, and sockets designed to accept only compatible plugs inserted in the correct orientation.

The term plug is in general and technical use in all forms of English, common alternatives being power plug, electric plug, and (in the UK) plug top. The normal technical term (in both British and International English) for an AC power socket is socket-outlet, but in non-technical common use a number of other terms are used. In British English the general term is socket, but there are numerous common alternatives, including power point, plug socket, wall socket, and wall plug. In American English receptacle and outlet are common, sometimes with qualifiers such as wall outlet, electrical outlet and electrical receptacle, all of these sometimes to be found in the same document., Tamper Resistant Receptacles, Electrical Safety Foundation International, 2009, (retrieved 1 March 2013 from ESFI)

Electrical sockets for industrial, commercial and domestic purposes generally provide two or more current carrying (live) connections to the supply conductors. These connections are classified as poles. A pole will be either a neutral connection or a line

Neutral is usually very near to earth potential, usually being earthed either at the distribution board or at the substation. Line (also known as phase or hot, and commonly, but technically incorrectly, as live) carries the full supply voltage relative to the neutral (and to earth).

Single phase sockets are classified as two pole (2P) and provide a single line contact and a neutral contact. In addition, a protective earth (Ground in American terminology) contact is usually, but not always, present, in which case the socket is classified as two pole and earth(2P+E).

Three phase sockets provide three line contacts, they may also include either or both of a neutral and protective earth contact. The designations of the three contacts may vary. The IEC standards use the Line designations L1, L2 and L3. NEMA standards use the Phase designations X, Y and Z.

Sockets intended for use with the American split Phase distribution system may have two line contacts and neutral. In this case the line designators X and Y are used. They may also include a protective earth contact.

World

IEC 60309 system

The most common range of heavy commercial and industrial connectors (particularly in Europe) 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).

The maximum voltage rating of IEC 60309 connectors is 1000 V DC or AC; the maximum current rating is 800 A; and the maximum frequency 500 Hz. Plugs are available in P+N+E (unbalanced single phase with neutral), 2P+E (balanced single phase), 3P+E (3 phase without neutral), and 3P+N+E (three phase with neutral). Current ratings available include 16 A, 32 A, 63 A, 125 A and 200 A.

Voltage rating and other characteristics are represented by a colour code (in three-phase plugs the stated voltage is the phase-phase voltage, not the phase-neutral voltage). Plugs have the earth pin of a larger diameter than the others, and located in different places depending on the voltage rating, making it impossible to mate, for instance, a blue plug with a yellow socket. Since the different current ratings have different overall sizes, it is also not possible to mate different pin configurations or current ratings. For example, a 16 A 3P+E 400 V plug will not mate with a 16 A 3P+N+E 400 V socket and a 16 A P+N+E 230 V plug will not mate with a 32 A P+N+E 230 V socket.

Yellow 2P+E, blue P+N+E, yellow 3P+E, red 3P+E, and red 3P+N+E are by far the most common arrangements. Blue P+N+E sockets (generally 16 A, although 32 A is becoming more common) are used as standard by British and Danish campsites and yacht marinas to provide 240 V domestic mains power to frame-tents, trailer-tents, caravans, and boats; they are also used elsewhere in Europe for the same purpose, though in some countries the local domestic plug is also widely used. Static caravans generally use the similar 32 A version because of the requirement to power electrical cooking and heating appliances. The blue P+N+E 16 A version carrying 240 V is also used in shopping malls and their peripherals to power 'temporary' stalls not incorporated within a lock-up shop, there is also use in domestic gardens within Britain to power garden equipment, barbecues, and temporary lighting. The yellow 2P+E 16 A version carrying 115 V is used extensively on the London Underground railway system to power temporary usage of heavy-duty fans; it is also frequently used by tradesmen within the UK, built into a portable transformer box that is powered from a standard 13 A 240 V mains supply, to run heavy-duty power-tools designed to operate at 115 V.

A small number of marinas provide 230 V single-phase power through a red three-phase connector (breaking the relevant standards in the process). This goes some way to ensuring that only boats that have paid the required fee (and thus obtained an appropriately made-up adaptor cable) are able to use the electricity.

For more detailed information, see the main article IEC 60309.

Throughout Europe, a common use of those industrial power connectors is in the entertainment and broadcast industries.

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.

Powerlocks are identified with the IEC 60446 harmonized colour code, they are also annotated as follows:

Cam-Loks are also available in these colours.

Where it is necessary to run separate feeds through multicable, the Socapex 19-pin connector is often encountered on theatre and studio lighting rigs.

Europe

Most of Europe use the common IEC 60309 type, but there are some exceptions:

UK: Lewden plugs Lewden plugs and sockets are metal bodied waterproof plugs and sockets made by Lewden. The pin arrangements of the smaller single phase varieties are the same as BS 1363 and BS 546 plugs and sockets. These plugs and sockets will mate with normal plugs and sockets of the same pin arrangement but they are only waterproof when a Lewden plug is used in a Lewden socket and the screw ring is properly tightened (sockets have a metal cover that screws on to waterproof them when not in use).

UK: BS 196 In 1930, the BS 196 standard for industrial plugs and sockets was introduced. The plugs are available in 5 A, 15 A and 30 A variants, with various configurations of keyways and pins to cater for different voltages. BS 196 plugs have now been superseded by BS 4343 (CEE type) connectors in most modern applications.

Sweden, Germany and Netherlands: Perilex plugs

Perilex plugs and sockets are 5-pin 3-phase connectors. The system provides 400 V 3P+N+PE and exists in 16 A and 25 A versions. In Sweden, the 16 A is generally used for stoves and to some extent for other heating devices in kitchens. In the Netherlands, Perilex is also used to connect fans with wired speed control (Switched L2 and L3 pins), but fans may not use three phase power

Sweden: Semko 17 plugs Semko 17 were 3/4-pin 3-phase connectors, with (4-pin) or without (3-pin) a neutral connector. Earth were provided via the shield. The connectors were available in different sizes, 16 A with rounded corners; 25 A and 63 A were rectangular. These connectors were used mainly in industrial and agricultural installations. Manufacturing and selling of Semko-17 connectors with metal shells was prohibited in 1989. A few years later manufacturing and selling of all Semko-17 connectors were prohibited. Existing connectors may be used but not by any employee (prohibited by "Arbetsmiljöverket"). The reason for the prohibition is that Semko-17 had several safety issues. The ground connection can become oxidized and when the shells are made of metal any ground fault goes right through the hands of a person connecting/disconnecting a male and a female cable connector (unless the person wears insulating gloves). Incorrect use of the ground connector as a neutral was not uncommon. Perhaps the worst issue is that in some connectors the ground screw could rust so severely that the ground wire comes loose and in the worst case make contact with a line (phase) wire nearby.

Switzerland: SN 441011

The Swiss standard SN 441011 (until 2019 SEV 1011) Plugs and socket-outlets for household and similar purposes. defines a hierarchical system of plugs and sockets including both single and three phase connectors. Sockets will accept plugs with the same or fewer number of pins and the same or lower ratings. Single phase Swiss plugs and sockets are described in the main article SN 441011.

The type 15 plug and socket has 3 round pins of 4 mm diameter, plus 2 flat pins (for L2 and L3). It is designed for three phase applications and is rated at 10 A, 250 V/440 V. The socket will also accept types 11 and 12 plugs, and the Europlug.