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plugs and sockets |
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plugs and sockets |
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America is a mine of interesting plugs and sockets. Different
devices for 125V, 208V, 250V, 277V and higher, rated at 15A,
20A, 30A, 50A or 60A; single phase, split-phase or three-phase
systems. The four plugs at right illustrate the variation in pin
configuration starting with a basic domestic 125V-15A type B plug
(bottom, left). Moreover, many plugs are available in a straight blade and a locking
design (see nos. 17-20). There are over 50 types in the category heavy duty, but even a museum can't have all of them. The images below show a small, but reasonably representative selection. For each plug and socket the official US code is stated, given by the National Electrical Manufacturers Association. The NEMA code provides the following information: first number: class of device (voltage dependent); second number: maximum tolerated current: P: plug; R: receptacle (= socket). |
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| 1, 2 | 125V, 30A socket and plug (NEMA 5-30R,P). The plug measures 11 x 6.5 x 4.8 cm (3.2 to 3.6 cm long pins excluded). It can handle a 2.5 cm thick cable. Huge compare to a 125V - 15A plug and therefore a typical example of 'heavy duty'. It is more likely to expect such devices at farms and workshops than residences. |
| 3, 4 | 277V, 15A socket and plug (NEMA 7-15R,P). 277V is the result of a neutral to ground connection in a 480V three-phase circuit (see page on three-phase transformers). In a workshop where 480V is nessesary, it might be more economic to use 277V single phase for lighting. Various 277V types of lamp are available, as incandescent lamps, screw base compact fluorescent light bulbs, fluorescent tube lights and LED lighting. |
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| 5 | 250V, 15A socket (NEMA 6-15R). The corresponding plug is one of the four plugs shown in the image top right (NEMA 6-15P). |
| 6, 7 | 250V, 20A socket and plug, without earth pin (NEMA 2-20R,P). The socket is an older design by Hubbell; the plug has been bought in 2000. |
| 8 | Components of an 'assemble-your-own' 250V, 30A or 50A plug (NEMA 6-30P or 6-50P). Images no. 10 and 12 show the results. The kit also allows the construction of new, non-existing plug types; an interesting feature, but unfortunately an A-Y-O socket does not exist. |
| 9, 10 | 250V, 30A socket and plug (NEMA 6-30R,P). |
| 11, 12 | 250V, 50A socket and plug (NEMA 6-50R,P). |
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| 13, 14 | 125/250V, 30A split-phase socket and
plug
(NEMA 14-30R,P). GND: earth connection (= equipment ground); W: ground,
comparable to neutral. Y-W = X-W = 125V; X-Y = 250V. Plug no. 14 is a
part of a
(replacement)
power supply cord recommended for dryers. The next page, on Japanese heavy duty plugs and sockets, has a scheme that explains the principle of split-phase electrical power. |
| 15, 16 | 125/250V, 50A split-phase socket and plug (NEMA 14-50R,P). See no. 13 for explanation of abbreviations. Plug no. 16 is recommended for electric stoves. |
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| 17, 18 | 250V, 30A locking socket and plug (NEMA L6-30R,P). |
| 19 | 600V, 30A 3-phase locking connector and plug (NEMA L17-30R,P). The angled pin (right) = equipment ground. Any combination of two of the three other pins gives 600V. This four wire device does not have a system ground (neutral in a Y-shaped 3-phase transformer). In a high voltage distribution system it is common not to have a neutral wire because loads are connected phase to phase. |
| 20 | 277/480V, 30A locking plug (NEMA L22-30P). The center triangular pin is the equipment ground. N = 3-phase system ground (neutral in an Y-shaped 3-phase transformer). X-N = Y-N = Z-N = 277V (single phase). X-Y = X-Z = Y-Z = 480V (three-phase, comparable to L1, L2 and L3 in IEC 60309 and other European three-phase systems). This plug is an older Hubbell type. Newer models have a round equipment ground pin. |
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