NEMA 8 devices are specified for three wire, two-pole, grounding devices for 480 volts. NEMA 13 series devices are three wire, three-pole, non-grounding devices for 3-phase, 600-volt equipment. NEMA 12 series devices are three wire, three-pole, non-grounding devices for 3-phase, 480-volt equipment. Identically to the NEMA 3 series, this is "reserved for future configurations" and no designs for this series exist and no devices have been manufactured. Moulded plugs for unearthed, double-insulated appliances may instead have a non-conductive plastic pin (an Insulated Shutter Opening Device or ISOD) the same size and shape as an earth pin, to open the shutters. In addition to the dangers of breaking a ground connection, removing the ground pin to make it fit a 1-15R receptacle or extension cord, may result in the live-neutral polarity being lost. NEMA standards exist for 1-15P, 1-20P and 1-30P plugs, and the 1-15R receptacle. Although standards exist for 2-15, 2-20 and 2-30, this series is obsolete, and only Hubbell still manufactures 2-20 devices (for repair purposes). All NEMA 6 devices are three-wire grounding devices (hot-hot-ground) used for 208 and 240 V circuits and rated for 250 V maximum, with the 6-15, 6-20 and 6-30 being grounding versions of the 2-15, 2-20 and 2-30, respectively.

NEMA 6 devices, while specified as 250 V, may be used for either 208 or 240 V circuits, generally depending on whether the building has a three-phase or split-phase power supply, respectively. All NEMA 2 devices are two-wire non-grounding devices (hot-hot) rated for 250 V maximum. 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. The 6-50 receptacle charges electric vehicles at the same 32- or 40-ampere maximum from charging stations, on a short cord, as the more versatile 14-50 with its fourth prong neutral not used currently for any electric vehicle charging purposes. 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 5-30 and 5-50 are physically larger, with 1 in (25.4 mm) between power pins; 5-30 also has an L-shaped neutral blade. 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. Unlike armored cables and other limited options, Metal Clad Cables are fit for any type of electrical needs, from home use to warehouses, hotels, offices, and even stadiums and industrial plants. British access to transatlantic cables and its codebreaking expertise led to the Zimmermann Telegram incident that contributed to the US joining the war. From the 1850s until well into the 20th century, British submarine cable systems dominated the world system. Newer NEMA 1-15 plugs with wider protective faces (middle right) have a safety advantage; plugs for electric toys (right) as well as very early plugs (left) have noticeably wide faces to discourage touching the electrical contacts. 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).

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. 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. All NEMA 5 devices are three-wire grounding devices (hot-neutral-ground) rated for 125 V maximum, with the 5-15, 5-20 and 5-30 being grounded versions of the 1-15, 1-20 and 1-30, respectively. In 1858, the steamship Elba was used to lay a telegraph cable from Jersey to Guernsey, on to Alderney and then to Weymouth, the cable being completed successfully in September of that year. The higher-current receptacles are rare, with twist-locking plugs such as L6-30 and direct wiring being more common. These larger sizes are uncommon, as twist-locking plugs are generally used for high-current applications.

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