Industrial multiphase power plugs sockets
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Industrial power plug is used here to refer to those power connectors that, unlike 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.
Some plugs are borderline cases. 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 US goes so far as to use two phases for larger domestic appliances: these can be either split phase (from a centre tapped transformer) or two phases from a 3-phase system. 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.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 systems have several advantages: first, they provide a better ratio of cable size to maximum voltage present; second, they allow a higher voltage present on trunk lines than is finally fed into single-phase appliances (though split phase can also achive this); and third, they allow large motors and generators to operate far more efficiently.
Almost all three-phase power plugs have an earth (also known as "ground") connection, but many do not have a neutral, because large appliances such as circular saws, air conditioners, 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 amp) and the L21-20 (20 amp) both of which have five pins (earth, neutral, and X, Y, Z phases).
Countries have different standards and regulations (or lack of them) for industrial power plugs, but there are also international standards and norms. The colour-coding of wires, etc. may or may not be the same as for normal mains plugs.
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Europe
in europe the range of plugs to IEC.309 and BS EN.60309-2 (the two refer to the same plug types though BS EN specifications tend to be stricter). Theese are often refered to in the UK as CEE industrial or simply CEE plugs. 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 realtive to the earth pin so it is impossible to mate a blue plug with a yellow socket the voltage ranges are 25V: purple 50V: white 100V-130V:yellow 200V-250V:blue 346-460V:red 500-750V:black high frequency >50V: green plugs are availible in 2P+E (single phase) 3P+E (3 phase no neutral) and 3P+N+E (three phase with neutral) current ratings availible are 16A 32A 63A and 125A there is a very nice summary of this info on http://www.mkelectric.co.uk/PDF/select/296.pdf
North America
Type L21
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L21-30 Plug and recepticle. The middle prong is ground, and the prong nearest the "L2130P" indicia on the plug is neutral |
The type L21-30-P and L21-20-P are 30 Amp and 20 Amp plugs for 208Y/120V connections. These plugs connect to type L21-30-R and type L21-20-R receptacles, respectively.
NEMA 5-20, 5-30, 5-50, 6-15, 6-20, 6-30, and 6-50
These are variants on the 5-15 plug. The 20 A plug has the neutral pin rotated 90 degrees, and the receptacle has a T-shaped neutral hole, to accept both 5-15 and 5-20 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.
The 6-15, 6-20, 6-30, and 6-50 are 250 V variants, with the 6-15 and 6-20 being grounded versions of the 2-15 and 2-20; again, 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 electric clothes dryers and ranges, and the occasional home arc welder. There are other configurations, both twist-lock and otherwise, for higher voltages and currents, and for more conductors.
Nema 14-30 and 14-50
theese offer 2 hots and a neutral allowing for both 120V and 240V (or a bit lower if the supply system is three phase) appliances
Duplexing and triplexing
Most receptacles in America 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 2pole 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 3phase 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.
External links
- Georgia State University physics department page on household wiring (http://hyperphysics.phy-astr.gsu.edu/hbase/electric/hsehld.html#c2).
- Diagrams of NEMA socket configurations from a vendor of plugs and receptacles (http://www.et-sales.com/Receptacles.htm)
- lots of diagrams of locking american recepticles (http://www.stayonline.com/reference/nema_twistlock.asp)
- lots of diagrams of non-locking american recepticles (http://www.stayonline.com/reference/nema_straight_blade.asp)
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