NEMA connector

 

 

NEMA connectors are power plugs and receptacles used for AC mains electricity in North America and other countries that use the standards set by the US National Electrical Manufacturers Association. NEMA wiring devices are made in current ratings from 15 to 60 amperes (A), with voltage ratings from 125 to 600 volts (V). Different combinations of contact blade widths, shapes, orientation, and dimensions create non-interchangeable connectors that are unique for each combination of voltage, electric current carrying capacity, and grounding system.
NEMA wall receptacles can be found installed in any orientation. Neither NEMA nor the US National Electrical Code nor the Canadian Electrical Code specify a preferred orientation, but the National Electrical Contractors Association's National Electrical Installation Standards (NECA 130-2010) specify that the preferred location of the ground is on top. When the ground blade of a receptacle is on the bottom, the neutral blade is on the upper left and the hot blade is on the upper right. All descriptions below assume this orientation (i.e. clockwise order is ground, neutral, hot for 120 V receptacle versions; and counter-clockwise for plug versions).
The Japanese plug and socket with narrow faces appear and works physically identical to NEMA 1-15, and such non-grounded receptacles are still common in Japan (though grounded 5-15R and 5-20R receptacles are slowly becoming more common). The Japanese system incorporates stricter dimensional requirements for the plug housing, different marking requirements, and mandatory testing and approval by METI or JIS.
In 46 of the 50 United States and all of Canada, tamper-resistant receptacles are required in new residential construction as of November 2013. These prevent contact by objects like keys or paper clips inserted into the socket. This is accomplished by an interlocking mechanism that requires hot and neutral blades inserted simultaneously to release the small doors blocking the slots. The grounding slot is not blocked by a door.
The 30 A plug and receptacle look similar to the 15 A one but larger. The higher-current versions are rare, with twist-locking plugs such as L6-30 or direct wiring 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. Single-phase 6-50 is commonly used on farms for silo unloaders, and is used with a 6-gauge flexible power cord up to 200 ft (61 m) long. The 6-50 is also used on arc welders. Some manufacturers of electric vehicle charging stations equip their 30-40 A Level 2 EVSEs with a 6-50 plug on a short cord, though it is becoming less common, with manufacturers now favoring the more common 14-50 plug.
NEMA 10 connectors are a now deprecated type that had formerly been popular in the United States for use with high-wattage electric clothes dryers, kitchen ranges, and other high-power equipment. NEMA 14-30R and -50R connectors are have generally replaced NEMA 10 equipment for these applications. NEMA 10s are classified as 125/250 V non-grounding (hot-hot-neutral), and were designed to be used in a manner that indirectly grounds the appliance frame, though not in the manner consistent with most modern practice. The older practice was common before the requirement of a separate safety ground was incorporated in the National Electrical Code.
The NEMA 14 devices are four-wire grounding devices (hot-hot-neutral-ground) available in ratings from 15 to 60 A. The voltage rating is 250 V. Of the straight-blade NEMA 14 devices, only the 14-30 and 14-50 are in common use. The 14-30 is used for electric clothes dryers, the 14-50 is used for electric cooking ranges, and either may also be used for home charging of electric vehicles. The NEMA 14 connectors are essentially the replacements for the older NEMA 10 connectors described above, but with the addition of a dedicated grounding connection.
NEMA 21 series devices are specified for three-pole plus neutral, five-wire grounding devices for 3 phase 120/208Y supplies. According to NEMA, NEMA 21 straight-blade devices are "reserved for future configurations," so no designs for this series exist and no devices have been manufactured. There are however NEMA L21 series locking devices for 20 and 30 amp devices specified and available for these applications.