Industrial and multiphase power plugs and sockets

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 when more than two current carrying conductors (polyphase system), high currents and/or protection from environmental hazards (particularly water) are required.

In many countries sockets are available that completely enclose a normal plug and have seals around the cable to exclude water. These reduce the need for special plugs and sockets but are often only suitable for fixed sockets due to their bulk, shape, and cable entry arrangements. Sockets on domestic extension leads are usually either not covered at all or covered with small covers that don't enclose an inserted plug.

Some connectors exist that are neither industrial nor multiphase but have higher voltage or current ratings than the normal plugs and sockets (e.g., the 16 A Italian socket and the 20 A American sockets). These are listed in the AC power plugs and sockets article grouped with the normal plugs and sockets of which they are variants.

Almost all three-phase power plugs have an earth (ground) connection, but may not have a neutral, because large equipment (circular saws, welding sets, pumps, air conditioners) tend to be delta connected. 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).

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.


Europe-wide IEC 60309 system

In Europe the most common range of heavy commercial and industrial plugs 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 or simply CEE plugs, or as "commando connectors" (presumably after the MK Commando range that contains these connectors).

Plugs are available in 2P+E (single phase), 3P+E (3 phase no neutral), and 3P+N+E (three phase with neutral). Current ratings available are 16 A, 32 A, 63 A, 125 A and 200 A.

Voltage is represented by a color code (in three-phase plugs the stated voltage is the phase-phase voltage, not the phase-neutral voltage). The different voltages 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 2P+E 230 V plug will not mate with a 32 A 2P+E 230 V socket.

The voltage ranges are::25 V: purple:50 V: white:100–130 V: yellow:200–250 V: blue:346–460 V: red:500–750 V: black

Green is used for high frequency systems of any voltage over 50 V

Yellow 2P+E, blue 2P+E, yellow 3P+E, red 3P+E, and red 3P+N+E are by far the most common arrangements. Blue 2P+E sockets (generally 16 A although 32 A is becoming more common) are used near-universally by UK campsites and yacht marinas to provide domestic mains power to caravans or boats; they are also used elsewhere in Europe for the same purpose, though in some countries the local domestic plug is also widely used.

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

A chart showing all available ratings and their key positions can be found at [ here] (PDF).

Entertainment Industry

Throughout Europe one of the common uses of industrial power connectors is in the Professional Sound, Video and Lighting industry where there is a need for vast amounts of power, delivered through quickly pluggable and unpluggable connectors. In this industry they are referred to as 'Ceeform' connectors. 230V single-phase (blue) and 400V three-phase (red). Connectors between 16A and 125A ratings are used.

Where more power is required, Powerlocks or Camlocs are the choice. These systems are normally used to distribute high current 3PH power, they are single pole, so 5 are required for a 3PH+N=E supply. Powerlocks have a rating of 400A or 600A each. Camlocs E1016 Series are rated at 600V 315A.

Powerlocks are identified with the European harmonised colour code, they are also annotated as follows
Green---Earth Camlocs are also available in these colours.

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).

weden, Germany & Netherlands: Perilex plugs

Perilex plugs and sockets are 5 pin multi phase connectors used in Sweden for residential installations. They are commonly used for stoves and washing machines. The system provides 400V 3P+N+PE.For more information, read these article in [ Dutch] or [ German] wikipedia

North America

Pin and Sleeve

Pin and Sleeve circular connectors are not compatible with the newer IEC 309 type. Current ratings are 30, 60, 100, 200, and 400 amperes. All are rated for voltages up to 250 volts DC or 600 V AC. Contact arrangements are from 2 to 4 pins. There are two “styles” depending on the treatment of the ground. Style 1 grounds only on the shell. Style 2 uses one of the contacts as well as the shell, internally connected together. They are not strongly typed for specific circuits and voltages as the IEC 309 are. One insert rotation option is available to prevent mating of similar connectors with different voltages.

The contacts in the plug are simple cylinders (sleeves), while the pin contacts in the receptacle have the spring arrangement to hold contact pressure, the reverse of the IEC 309 type connectors. All contacts are the same diameter. Originally metal construction was used, but now they are also made with plastic shells. Since only keying in the connector shell is used, and since the keys can be damaged in industrial use, it is possible to mis-match worn connectors.

NEMA connectors

NEMA devices are not exclusively industrial devices, and some types are found in nearly all buildings in the United States. Many of these standards are identical to their counterparts in Canada, although there are some exceptions. NEMA wiring devices are made in current ratings from 15 to 60 amperes, and voltage ratings from 125 V to 600 V.

There are two basic classifications of NEMA device: straight-blade and locking. The locking type is preferred in many industrial environments, while the residential and commercial environment is home to straight-blade devices. (Of course, the straight-blade 5-15 and 5-20 are found nearly everywhere.) Numbers prefixed by L are twistlock, others are straight blade.

NEMA 10-20, 10-30 and 10-50

NEMA 10 devices are a curious throwback to an earlier time. They are classified as 125/250 V non-grounding, yet they are usually used in a manner that effectively grounds the appliance, albeit not in a manner consistent with most modern practice.

As commonly used, 10-30 and 10-50 plugs have the frame of the appliance grounded through the neutral pin. This was a legal grounding method under the National Electrical Code for electric ranges and electric clothes dryers from the 1947 to the 1996 edition. Since North American dryers and ranges have certain parts (timers, lights, fans, etc.) that run on 120 V, this means that the wire used for grounding is also carrying current. Although this is contrary to modern grounding practice, such installations remain extremely common in the United States and are relatively safe, because the larger conductors used are less likely to be broken than the smaller conductors used in ordinary appliance cords.

Persons moving their older appliances to newer NEMA 14-equipped buildings (or vice-versa) should have the cords replaced by a qualified electrician, as the grounding details may be quite confusing to the uninitiated.

NEMA 10-20 devices are very rare nowadays. There is also a similar obsolete design, lacking a NEMA configuration number, rated 125 V 15 A/ 250 V 10 A which is nearly identical to the AS/NZS 3112 standard used in Australia/New Zealand. These are also extremely rare.


The NEMA 14 devices are 4-wire grounding devices available in ratings from 15 A to 60 A. Of the straight-blade NEMA 14 devices, only the 14-30 and 14-50 are common. The voltage rating is a design maximum of 125/250 V. They are essentially the replacements for the connectors above with the addition of a separate grounding connection.

All NEMA 14 devices offer two hots, a neutral and a ground, allowing for both 120 V and 240 V (or 120 V and 208 V if the supply system is three phase wye rather than split phase or three phase center tapped delta) appliances. They differ in rating and shape of the neutral pin. The 14-30 has a rating of 30 A and an L-shaped neutral pin. The 14-50 has a rating of 50 A and a straight neutral pin sized so that it will not fit in the slot of a 14-30.

NEMA 14-30 devices are most commonly found serving electrically-heated clothes dryers, while 14-50 devices most commonly serve kitchen ranges. In the United States, these are generally found in buildings constructed after the 1996 National Electrical Code, although they are also found in considerably earlier mobile homes. In Canada, the use of NEMA 10 devices was discontinued much earlier (if it was ever permitted at all), so NEMA 14 devices are more common there.

Twist-locking connectors

L21-30 Plug and receptacle

Twist-locking connectors were first invented by Harvey Hubbell III in 1938 and "Twist-Lock" remains a registered trademark of Hubbell Incorporated to this day [ Hubbell Corporate History] ] , although the term tends to be used generically to refer to NEMA twist-locking connectors manufactured by any company. Unlike non-locking connectors, twist-locking connectors all use curved blades that have shapes that conform to portions of the circumference of a circle. Once pushed into the receptacle, the plug is twisted and its now-rotated prongs latch into the receptacle. To unlatch the plug, the rotation is reversed. The locking coupling makes for a very reliable connection in commercial and industrial settings.

Like non-locking connectors, these come in a variety of standardized configurations and follow the same general naming scheme except that they all begin with an "L" for "locking". Once again, the connector families are designed so that 120 V connectors , 208/240 V connectors, and various other, higher-voltage connectors can not be accidentally intermated [ Hubbell Twist-Lock Wiring Devices and Safety Enclosures] ] .


In Australia, New Zealand and some pacific islands a different standard is used. The plugs and sockets are manufactured by Clipsal (Australia) and PDL (New Zealand) respectively. The most common is arguably the 32A version of the clipsal 56 series, named after its IP 56 rating as can be in the [] . Also available are metal-clad and the 66 series and some European CEE standard outlets. The 56 series only allows metal-clad housings for 50amps and above, while the 66 series allows plastic housings with interlocks (cannot mate or separate some interlocking plugs with the power on) however it has a different pin configuration (AS3123).

Multiple pin version are available, 3 pins for single phase in 10, 20 and 32A, 4 pins for 3 phase motors that do not require neutral connection in 10A, 20A, 32A, 40A, 50A and 60A and 5 pins for equipment and distribution boards that require neutral and earth. 6 and 7 pin versions are also available in 10A & 20A in 56 series and 50A, 63A and 80A in 66 series with extra control pins. Since neutral is the central pin, 4 pin plugs will fit 5 pin sockets, but the same does not hold for 3 pin plugs. While all residential Australian sockets will accept plugs of a lower rating, apparently only 32A, 40A and 50A industrial sockets of the same series will accept plugs of lower ratings, but 10A and 20A are different again. For this reason it is prudent to check exactly which type of connector in terms of number of pins and amperage. Adaptor leads and boards are also quite common, however they can easily add up to thousands of dollars.

Duplexing and triplexing

Most receptacles in the USA and Canada are duplex receptacles. The top and bottom sockets can also be separated, if desired, and, for example, supplied by separate breakers with a common neutral. This is typically done in kitchens where a high load will likely be placed on both sockets. In this case, a common trip two-pole breaker is often used.

The concept of duplexing can be generalized to triplexing, so that three duplex receptacles can be supplied by a common neutral, from a three-phase supply. Typically, a three-pole common trip 15 A breaker is used to supply such a socket. This enables three single phase loads to be supplied in a phase-sequenced manner. The common-trip breaker is REQUIRED under the National Electrical Code. Motors can often run with loss of a single phase, however the motor will run hot and vibrate, a condition best avoided. An example of such a load is a light fixture having three bulbs. For flicker-free operation, three bulbs are each fitted with a separate plug, and driven 120° out of phase with one another, from a triplex receptacle. The top receptacles shown in the figure are fitted with neon night lights to indicate phase sequence, the triplex loads connect to the bottom receptacles.

Issues with dimmers

If done after passing through a bank of light dimmers that use a phase cutting technique, duplexing and triplexing can create problems. Harmonic "noise" created by dimming equipment can effectively overload a combined neutral and result in unreliable operation. Combined neutrals can also cause inconsistent response from individual circuits in this situation. Although not the case in older facilities, in all new installations of large-scale theatrical dimming equipment, manufacturers require individual neutrals after passing through the dimmers to maintain warranty status of the equipment.

Note that lots of theatrical dimming equipment actually uses shared neutrals prior to the dimming.For example, the Rosco Entertainment dimmers have a shared neutral on their plugs, where there are four conductors (not including ground) for neutral and the three hots, that feed the dimmer racks. While with a simple dimmer circuit the issue would be just as bad with a shared neutral either before or after the dimmer, filtering of the mains input makes this less of an issue.

ee also

*Domestic AC power plugs and sockets
*Double insulated
*Electrical power
*Ground and neutral
*Protective multiple earthing


Catalogue K1_Industrial Plugs and Sockets from SEZ a.s., Slovakia for download in PDF...
* [ ...Here]

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