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NEMA 15 are three-pole and ground connectors (phase A, phase B, phase C, ground) rated for 208 V. Intended for delta three-phase circuits with ground and no neutral. NEMA L1 series devices are single-pole plus neutral, two-wire, non-grounding devices for 125 volts single phase. Such conditions are common in rural or mountainous areas that are inaccessible to trucks. Since North American dryers and ranges have certain components (timers, lights, fans, etc.) that run on 120 V, this means that the neutral wire indirectly used for grounding would also carry current, even under non-fault conditions. The 14-30 is limited to 30 amperes (24 amperes continuous) and used mainly for some electric clothes dryers and some electric cooking stoves. These sockets and plugs are four prong (see receptacle chart above) 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 14-50 and 14-30 are in common use and either may be used for home charging of electric vehicles. These measures are collectively called 'reactive support'.

The hot and neutral blades are angled at 45° from vertical and 90° to each other, unlike NEMA 10 devices (where the angles are 30° and 60° respectively), also the plug is slightly smaller than a NEMA 10 and larger than ordinary 5-15P plugs. Locking receptacles appropriate for the voltage and current are used on the RV end of the cord, along with non-locking plugs on the end connecting to the pedestal. ML-series "Midget Locking" connectors are for 15 A applications where a larger locking connector would not fit. This is resolved in most cases by the connector having a robust integral strain relief. The NEMA TT-30 (TT stands for Travel Trailer) connector is a 120 V 30 A recreational vehicle standard (hot-neutral-ground), also known as RV 30. The TT-30R receptacle is commonly available in nearly all RV parks in the United States and Canada, and all but the largest RVs manufactured since the 1970s use this plug to connect to power feeds. The locking coupling makes for a more reliable connection in commercial and industrial settings, where vibration or incidental impact could disconnect a non-locking connector. 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 11 series devices are three wire, three-pole, non-grounding devices for 3-phase 250-volt designs and equipment parts are specified by NEMA for 20-ampere (11-20), 30-ampere (11-30), and 50-ampere (11-50) devices. NEMA 22 series devices are specified for three-pole plus neutral, five-wire grounding devices for 3-phase 277/480Y supplies. The higher-current receptacles are rare, with twist-locking plugs such as L6-30 and direct wiring being more common. 1994, to require plugs sold to meet the technical standard. As commonly used, 10-30 and 10-50 plugs required the frame of the appliance to be indirectly grounded via a strap connecting to the neutral blade. If the neutral conductor were to break, disconnect, or develop high resistance, the appliance frame could become energized to dangerous voltages. 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 to the neutral, which was common before the requirement of a separate safety ground was incorporated in the National Electrical Code. Submarine HVDC systems are often used to interconnect the electricity grids of islands, for example, between Great Britain and continental Europe, between Great Britain and Ireland, between Tasmania and the Australian mainland, between the North and South Islands of New Zealand, between New Jersey and New York City, and between New Jersey and Long Island.

The first three-phase alternating current using high voltage took place in 1891 during the international electricity exhibition in Frankfurt. The purpose of the NEC is to protect persons and property from hazards arising from the use of electricity. New construction, additions or major modifications must follow the relevant code for that jurisdiction, which is not necessarily the latest version of the NEC. Relying on the neutral conductor was a legal grounding method for electric ranges and clothes dryers, under the National Electrical Code from the 1947 to the 1993 editions (banned in 1996 edition). Electrical Construction and Maintenance Magazine, Conductors for General Use, Chapter 3 Articles in NEC, starting with Article 342 This section is expected to be modified to include cables in future editions. One apparent disadvantage of twist-lock connectors is that in the event that the cable is accidentally pulled too hard, rather than the plug falling out of the receptacle, exposed conductors may come out of the plug, causing dangerous shorts or shock hazards if the circuit is live. The straight blades all carry one of the three phases. NEMA 8 devices are specified for three wire, two-pole, grounding devices for 480 volts. NEMA 9 devices are specified for three wire, two-pole, what is electric cable grounding devices for 600 volts.