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Industrial power plug is used here to refer to those Power Connector s that, unlike ordinary mains power plugs, are not used for the average domestic appliance but rather for more heavy-duty applications such as Arc Welders , Cranes , Cinemas , large cooking ranges, etc. Besides the higher ratings, some types can be used outdoors or in environments where they are exposed to water, ice, sand, and chemicals. See Domestic AC Power Plugs And Sockets for further information. Some overlap exists between large residential and small industrial plugs and sockets. For instance, Italy has large, 16-ampere, three-prong plugs competing with the more normal 5-ampere ones, but modern sockets in homes take both types. The U.S. and Canada use a Three-wire System for larger domestic appliances, with sockets rated up to 50 amperes for cooking appliances. The situation in the United Kingdom is slightly more clear-cut, with BS 1363 plugs (3 to 13 amperes, depending on the fuse inside) almost universal in homes. The 5- and 15-ampere BS 546 plugs are occasionally seen in older homes, but this is getting rarer, and these plugs have remained in use in a few niche markets like theatre lighting. The IEC 60309 (formerly IEC 309) range of single and three-phase plugs are used mainly for industrial purposes, although most people in the UK will have seen the smaller varieties around swimming pools and caravan sites. Unlike domestic plugs, industrial connectors often use Three-phase rather than Single-phase electrical power. Such Polyphase System s allow use of efficient Induction Motor s. Almost all three-phase power plugs have an Earth (also known as "ground") connection, but may not have a Neutral , because large appliances such as Circular Saw s, Air Conditioner s, etc. tend to be delta connected. Such plugs have only four prongs (earth, and X, Y, Z 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 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 BS EN 60309-2 (formerly BS 4343 ) (the two refer to the same plug types though BS EN specifications tend to be stricter). 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). 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 key (or keys in the case of ELV plugs) in different places relative to the earth pin, therefore it is impossible to mate, for instance, a blue plug with a yellow socket. It is also not possible to mate different pin configurations or current ratings, therefore, 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. 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 :high frequency >50 V: green Plugs are available in P+N+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. Yellow P+N+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 near-universally by UK Campsite s and Yacht Marina s 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 240 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 comprehensive summary of this information can be seen here (PDF). 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 done up (sockets have a metal cover that screws on to waterproof them when not in use). 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. NEMA connectors NEMA devices are not exclusively industrial devices, but 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 125V to 600V. NEMA Nomenclature 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. The numeral preceding the hyphen in NEMA nomenclature indicates the configuration type, i.e. number of poles, number of wires, voltage, and whether single- or three-phase. A grounding type of device will be described as two-pole, three-wire; or four-pole, five-wire; etc. A non-grounding device will be two-pole, two wire; or three-pole, three-wire; etc. The numeral following the hyphen is the rating of the device in amperes. The number is followed by the letter R to indicate a receptacle or the letter P to indicate a plug. As an example, the 5-15R is the common 125V two-pole, three-wire receptacle. The L5-15R, while sharing the same rating, is a locking design which is not physically compatible with the straight-blade 5-15 design. The 5-30 has the same two-pole, three-wire configuration and 125V rating, but is rated 30 amperes. It should be noted that although there are several non-grounding device types in the NEMA standards, only a few of them are in widespread use today. These are the two-pole 1-15 , still in use in millions of buildings built before 1965, and the three-pole 10-30 and 10-50. NEMA 1 All NEMA 1 devices are two-wire non-grounding devices rated for 125V maximum. NEMA 1-15P are the two-prong plugs commonly found on household lamps and consumer electronics such as clocks and radios. Standards exist for 1-15P, 1-20P and 1-30P plugs, and the 1-15R receptacle. There are no 1-20R and 1-30R receptacles; 1-20P and 1-30P mate with a corresponding NEMA 5 receptacle. NEMA 2 All NEMA 2 devices are two-wire non-grounding devices rated for 250V maximum. Standards exist for 2-15, 2-20 and 2-30. There is no 2-15R receptacle; 2-15P mates with a corresponding NEMA 6 receptacle. NEMA 5 All NEMA 5 devices are three-wire grounding devices rated for 125V maximum, with the 5-15, 5-20 and 5-30 being grounded versions of the 1-15, 1-20 and 1-30, respectively. The 20 A plug has the neutral pin rotated 90 degrees, and the 5-20R receptacle may have a T-shaped neutral hole, to accept both 5-15P and 5-20P plugs. The 5-30 uses an L-shaped neutral, and both it and the 5-50 are over-sized, but these configurations are uncommon, as "twist-lock" plugs are generally used for high-current applications. NEMA 6 All NEMA 6 devices are three-wire grounding devices rated for 250V maximum, with the 6-15, 6-20 and 6-30 being grounded versions of the 2-15, 2-20 and 2-30, respectively. The 20 A plug has the neutral pin rotated 90 degrees, and the 6-20R receptacle may have a T-shaped neutral hole, to accept both 6-15P and 6-20P plugs. The higher-current versions are rare, with "twist-lock" plugs and direct wiring being far more common; generally 6-series non-locking plugs are used for such appliances as large room air conditioners, commercial kitchen equipment, and the occasional home Arc Welder . It should be remembered that NEMA 6 devices may be used for either 208V or 240V circuits. Do not assume that the presence of a NEMA 6 receptacle indicates the availability of 240V power. test NEMA 10-20, 10-30 and 10-50 NEMA 10 devices are a curious throwback to an earlier time. They are classified as 125/250V 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 120V, 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 125V 15A/ 250V 10A which is nearly identical to the AS/NZS 3112 standard used in Australia/New Zealand. These are also extremely rare. NEMA 14 The NEMA 14 devices are 4-wire grounding devices available in ratings from 15A to 60A. Of the straight-blade NEMA 14 devices, only the 14-30 and 14-50 are common. The voltage rating is a design maximum of 125/250V. They are essentially the replacements for the connectors above with the additon of a seperate grounding connection. All NEMA 14 devices offer two hots, a neutral and a ground, allowing for both 120V and 240V (or 120V and 208V 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 30A and an L-shaped neutral pin. The 14-50 has a rating of 50 A and a straight neutral pin. 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.
NEMA L21 The type L21-30-P and L21-20-P are 30 A and 20 A plugs for 208Y/120V three phase connections. These plugs connect to type L21-30-R and type L21-20-R receptacles, respectively. The middle prong is ground, and the prong with a right angle on the tab (nearest the "L2130P" indicia on the plug pictured) is neutral NEMA TT-30 NEMA TT-30 is a 30A 125 volt recreational vehicle standard which may also be known as RV 30. It is frequently (and sometimes disastrously) confused for a NEMA 10-30. The RV receptacle is common in nearly all RV parks in the United States and Canada, and all but the largest RVs manufactured in the last 30 years use this plug. The hot and neutral blades are angled at 90 degrees to each other, similar to NEMA 10 devices. The plug is slightly smaller than a NEMA 10 but larger than ordinary 5-15 plugs. The ground pin, however, is a U-shape, like those on straight-blade NEMA grounding devices. Due to the appearance of this plug, many people assume that it is to be wired for 240V. This is not the case! This is a 120V device. 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. 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, for triplex loads where proper phase sequence is desired. 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 many 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 is four conductors (not including ground) for neutral and the three hots, that feed the dimmer racks. See Distributed Dimming . 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. EXTERNAL LINKS
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