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IEC 60309 (formerly IEC 309, also published by CENELEC as EN 60309) is an international standard from the International Electrotechnical Commission (IEC) for "plugs, socket-outlets and couplers for industrial purposes". The highest voltage allowed by the standard is 690 V DC or AC; the highest current, 125 A; and the highest frequency, 500 Hz. The temperature range is −25 °C to 40 °C.
There is a range of plugs and sockets of different sizes with differing numbers of pins, depending on the current supplied and number of phases accommodated. The fittings also include limited (IP44) weather-proofing, that is one reason for choosing these fittings when the connections will be used in open-air conditions; a further reason for using these (other than when the heavy-current or three-phase facilities are actually needed), is to deter potential users from connecting domestic appliances to the sockets, as 'normal' domestic plug-tops will not fit.
The cable connectors and sockets are colour-coded, according to the voltage range and frequency used; for example, common colours are yellow for 100–130 volts and 50–60 Hz, blue for 200–250 volts and 50–60 Hz, and red for 400–480 volts and 50–60 Hz. Color codes depend on the highest, phase-to-phase, voltage. In addition to the colour-coding the voltage and frequency are encoded by the keyway position. The blue fittings are often used for providing weather-proofed exterior sockets for outdoor apparatus. The yellow fittings are used to provide transformer isolated 110 V supplies for UK construction sites to reduce the risk of electric shock and this use spills over into uses of power tools outside of the construction site environment. In camping situations, the large 32 A blue fittings provide power to static caravans, whilst the smaller blue 16 A version powers touring caravans and tents. The red three-phase versions are used for three-phase portable equipment.
IEC 60309-1 specifies general functional and safety requirements for any form of industrial high-current power connector. IEC 60309-2 specifies a range of mains power connectors with circular housings, and different numbers and arrangements of pins for different applications. IEC 60309-3 dealt with connectors for use in explosive gas environments, but was withdrawn in 1998.
The standardization was originally done by the CEE (Commission internationale de réglementation en vue de l'approbation de l'équipement électrique), being a European certification body that became the IECEE in 1985 (International Commission on the Rules for the Approval of Electrical Equipment) as part of the IEC. It is the same standardization body that had also catered for the home AC plugs in the "CEE 7" series (CEE 7/4 alias German Schuko, CEE 7/5 French and CEE 7/7 French/German hybrid plug, and later the CEE7/16 Europlug). The industrial sockets were standardized in the 1960s in the CEE 17 series that was adopted in the UK as BS 4343 and which were later to become the IEC 60309 standard.
IEC 60309-4 concerns switched socket-outlets and connector interlocks. In the United Kingdom, this standard was first adopted as BS 4343:1968 and has since been replaced by its European equivalent BS EN 60309-4. In the UK these plugs are often referred to as caravan, Commando (a brand name used by MK Electric), CEE industrial, CEEform or simply CEE plugs.
The colour of an IEC 60309 plug or socket indicates its voltage and frequency rating. The most widespread colours are yellow (125 V), blue (250 V), and red (400 V). The black version (500 V) can often be found on ships.
|100–130 V||Yellow||4||[note 1]|
|120/240 V||Orange||12||[note 2][note 3]|
|200–250 V||Blue||6||[note 4]|
|120–250 V||Blue||9||[note 5]|
|50–250 V DC||White||3|
|>250 V DC||White||8|
|277 V 60 Hz only||Grey||5||[note 4][note 2]|
|380 V 50 Hz only||Red||3||[note 5][note 6]|
|380–480 V||Red||6||[note 5]|
|380–480 V||Red||11||[note 7]|
|380–415 V||Red||9||[note 4]|
|440 V 60 Hz only||Red||3||[note 5][note 6]|
|480–500 V||Black||7||[note 5]|
|500–680 V||Black||5||[note 5]|
|100–300 Hz||Green||10||[note 8][note 6]|
|300–500 Hz||Green||2||[note 9][note 6]|
|Any of the above||Grey||12||[note 10]|
|None of the above||Grey||1||[note 11]|
- Single phase voltage or three phase line voltage (phase-phase) including supplies from an isolating transformer.
- For countries only where Series II current ratings (20, 30, 60, 100 amps) are used.
- North American 120/240 V single-phase system. Four pin (2P+N+E) connector only.
- Single phase.
- Three phase line voltage (phase-phase).
- Only available in 16 and 32 Amp sizes.
- Three phase line voltage (phase-phase) at 60 Hz only.
- Greater than 50 volts three phase line voltage (phase-phase). Not available in single phase version.
- Greater than 50 volts single phase or three phase line voltage (phase-phase).
- Single and 3 phase (3P+E only) supplied from an isolating transformer (except for yellow plug supplies).
- Most frequently used for low voltage supplies that do not fall into any of the specified ranges.
- All AC systems are either 50 or 60 Hz unless otherwise stated.
- All three phase plugs and socket are available in 3P+E or 3P+N+E (but see Note 7).
IEC 60309-2 connectors are produced in many variants, designed so that a plug of one type can only be inserted into a socket of the same type. Different current ratings (such as 16 A, 32 A, 63 A and 125 A) are distinguished by different diameters of the circular housing.
Different voltage and frequency combinations are distinguished by the location of the ground pin (or a plastic projection called the minor keyway, for connectors with no ground pin), as shown in the following table. The ground pin can be in one of twelve locations spaced at 30° intervals around the circle on which all the pins lie. The various positions are referenced from the view of the open side of a socket; the 6 o'clock (180°) position is at the same angle as the major keyway, and is oriented downwards. The major keyway is a projection on the plug casing that aligns with a notch on the socket. The ground pin has a larger diameter than the other pins, preventing the wrong type of plug being inserted in a socket.
|Pin configuration (P: power, N: neutral, E: earth or ground)|
|60° / 2h||>50 V 300–500 Hz green housing||>50 V 300–500 Hz green housing||>50 V 300–500 Hz green housing|
|90° / 3h||50–250 V DC||380 V 50 Hz
440 V 60 Hz red housing
|220/380 V 50 Hz
250/440 V 60 Hz
|120° / 4h||100–130 V AC yellow housing||100–130 V AC yellow housing||57–75/100–130 V AC yellow housing|
|150° / 5h||277 V 60 Hz grey housing||600–690 V AC black housing||347–400/600–690 V AC black housing|
|180° / 6h||200–250 V AC blue housing||380–415 V AC red housing||200–240/346–415 V AC red housing|
|210° / 7h||480–500 V AC black housing||480–500 V AC black housing||277–288/480–500 V AC black housing|
|240° / 8h||250 V DC|
|270° / 9h||380–415 V AC red housing||200–250 V AC blue housing||120–144/208–250 V AC blue housing|
|300° / 10h||>50 V, 100–300 Hz green housing|
|330° / 11h||440–460 V 60 Hz red housing||250–265/440—460 V 60 Hz, red housing|
|360° / 12h||125/250 V
single phase (2P+N+E)
- A six-pole plus earth (6P+E) version also exists. This is commonly used for star-delta starting of three-phase motors.
Connectors rated at 63 A and 125 A may optionally be equipped with a pilot contact. This smaller pin in the centre of the connector is designed to 'make' after all the other pins when connecting a plug and socket, and to 'break' first when disconnecting. It is used to control the supply of power at the source. This is useful as disconnecting under load will cause arcing which may cause damage to both the plug and socket, and risk injury to the user.
The most common plug types are:
- CEE yellow 2P+E
- CEE blue 2P+E
- CEE yellow 3P+E
- CEE blue 3P+E
- CEE red 3P+N+E
The colour of the casing refers to the regional electric power distribution at:
- 110/120 Volt = yellow
- 230/240 Volt = blue
- 400 Volt = red.
Red 3P+N+E, 6h 
The red 3P+N+E, 6h (180°) plug allows to connection to the widespread 400 V three phase power network. The most common ratings are 16 A, 32 A and 63 A, with 125 A and 200 A less common. Construction sites in central Europe have most of their higher power cabling setup with this three phase socket type as the single phase to neutral voltage of 230 V is available for other devices. So called power splitters with this connector as a 3 phase inlet and 3 groups of single phase outputs with individual circuit breakers are generally used to achieve this, and allow load balancing across the phases, important on generator supplies. Similar configurations are used for outdoor exhibitions, festivals and large events.
The five pins are positioned in a circle with the ground connector E to be thicker and longer than the network pins. When looking at the socket, the phase sequence should be L1, L2, L3. Since some wiring may be reversed, which could make motors turn backward, many machines on construction sites feature a phase swap plug that allows to swap two pins and so reverse the phase sequence.
Three-phase electric motors do not need the neutral wire to function, so that there is also a Red four pin variant (3 phases and earth) of the IEC 60309 plugs for three phase power. The two styles are not intermatable, to prevent a potental floating neutral.
Blue P+N+E, 6h 
The blue P+N+E, 6h (180°) plug is a single phase connector. In particular the smallest (16 A) variant has become especially common in camping vehicles and sockets found in caravan parks and marinas throughout Europe. The so-called 'Caravan Mains Socket' has almost universally replaced a wide variety of other national 230 V domestic plugs since they are pan-European and inherently safe to standard IP44. On larger temporary buildings, particularly with electric heating the larger 32 A is more common. It should be noted that not all such installations distinguish the live (phase) and neutral conductors, and reverse wired sockets are quite common, so double pole breaking RCDs and main switches are recommended. When sockets are mounted looking downwards then the connector system is rated for outdoor use in all weather. This is also the standard connector for lighting equipment (up to 16 A) used in the British film and television industry. (often as outlets from a power splitter with a higher rated 3 phase input)
Yellow P+N+E, 4h 
The yellow P+N+E, 4h (120°) plug is a single phase connector that is in widespread use on the British Isles for 110 V building site and fairground applications. A popular model if this socket type is marketed under the brand name MK Commando which leads to all IEC 60309 sockets to be (incorrectly) referred to as Commando sockets in some descriptions.
Blue 3P+N+E, 9h
The blue 3P+N+E, 9h (270°) plug is a three phase connector available in areas with both 110 V and 240 V supply systems (mains). It is prevalent in the outdoor event lighting and audio power industry as an outdoor-safe replacement for NEMA-connectors. In the United States it is not usually used for three phase power but for the high leg delta wiring of split-phase electric power (unknown in Europe). This allows one to choose single-phase AC power at either 110–120 volts between phase and neutral or 220–240 volts between phase and phase. Since these two modes do not need three phases there is also a yellow four-pin connector available designed for a single-phase 110–120 or 220–240-volt load.
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- Scope section 1, International Standard 60309-1 edition 4.1 Part 1 General Requirements , 2005, International Electrotechnical Commission, page 13
- BS EN 60309-1, IEC 60309-1: "Plugs, socket-outlets and couplers for industrial purposes. General requirements." (1999/2012)
- BS EN 60309-2, IEC 60309-2: "Plugs, socket-outlets and couplers for industrial purposes. Dimensional interchangeability requirements for pin and contact-tube accessories." (1999/2012)
- "General Introduction of CEE plugs and receptacles". Rey & Lenferna. MENNEKES industrial plugs and receptacles. Retrieved 2011-09-03. "History: CEE plugs and sockets base on the CEE 17 standard (also BS 4343) which was introduced in the 1960s and that later led to the IEC 60309 standard."
- BS EN 60309-4: "Plugs, socket-outlets and couplers for industrial purposes. Switched socket-outlets and connectors with or without interlock." (2007/2012)