Museum of Plugs and Sockets logo, small   U.S. dual Amperage  and/or
dual Voltage sockets      
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NEMA 5-20R Flat blade configuration of US 15-20A, 125-250V receptacles NEMA 6-20R US dual voltage 15-20A receptacle
NEMA 5-15P NEMA 5-20P NEMA 6-15P NEMA 6-20P

1 Most US sockets for 20A plugs are designed in a way that they can also be used for 15A plugs. The image shows a duplex socket rated at 125V, 20A (NEMA 5-20R). See nos. 5 and 6 for corresponding plugs.
2 Scheme that illustrates which parts of slots are used for 125 or 250 Volt and 15 or 20 Amp plugs.
3 Combined 250 V, 15 and 20 A socket (NEMA 6-20R). This voltage is frequently used in North America for more heavy duty applications. See nos. 7 and 8 for corresponding plugs. Image no. 14 shows the Canadian version of this socket.
4 Dual amperage (15-20A) and dual voltage (125-250V) duplex socket. This device accepts each of the plugs shown in images 5 to 8. See image nos. 10 and 11 for details.
There are some more
special combination duplex sockets. Also combinations of flat blade and twist-lock devices exist.
5 15A - 125V grounded plug (NEMA 5-15P). Brand name: Leviton, USA.
6 20A - 125V grounded plug (NEMA 5-20P). Brand name: Leviton, USA.
7 15A - 250V grounded plug (NEMA 6-15P). Brand name: Eagle, USA
8 20A - 250V grounded plug (NEMA 6-20P). Brand name: Hubbell, USA


US dual voltage 15-20A wiring scheme US dual voltage 15-20A receptacle, details

9, 10
The above scheme comes with the Leviton dual amperage / dual voltage socket shown in image nos 4 and 10. Duplex sockets usually have break-away tabs to separate the top and bottom outlet. In the Leviton leaflet it is indicated as Break-Off Fin. Image no. 10 shows a duplex receptacle with an intact fin (green arrow). Breaking the fin allows placing the two outlets on separate circuits, each with its own breaker.
Two branch circuits may share a neutral terminating on duplex sockets, a condition sometimes referred to as "split-wiring", "split-receptacle", or "split feed".


NEMA 10-20R US split-phase wiring scheme NEMA 6-20R, Canadian variant

11 Split-phase wiring (see scheme at right) allows the choice of 120 or 240 Volt in a single outlet. The socket shown is a NEMA 10-20R 3 pole, 3 wire non-grounding receptacle*. Brand name: Eagle Electric. The combination of slots W and Y (or X) gives 120V, whereas X-Y offers 240V. Comparable sockets exist for 30A and 50A. A 15A-125V / 10A-250V variant is now phased out. For household applications (for example ranges and dryers) NEMA class 14 sockets and plugs are used, which have an additional equipment ground wire (see examples in the heavy duty section).
* the matching plug is identical to the Japanese 20A split-phase plug, and the Brazilian 20A "tristinha" plug.
12 Split-phase wiring, which is commonly used is U.S. homes, has two live wires ('hot' in American English), whereas the neutral wire is a grounded center-tap of the secondary coil of the transformer; see scheme. A combination of live-1 (X) or live-2 (Y) and neutral (W) offers 120V. Because of alternating current live-1 and -2 are out of phase and can be combined to offer 240V.
The scheme is based on information given on the HyperPhysics site (Georgia State University).
13 NEMA 6-20R, Canadian version. NEMA 5-20R (no. 1) and 6-20R (no. 3) for the US market have a T-shaped neutral slot so they will accept both 15A and 20A plugs. The Canadian ones have to be designed to accept 20A plugs only. Brand name: Bryant Hubbell.


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