NEMA is an American-based organization formed in 1926 which sets the standards for electrical components and systems to adhere to and maintain.
Almost all of the electrical plugs and electrical receptacles used and sold in the US abide by the manufacturing and material quality standards set by NEMA. An important result of this is the increased consistency and expectations between electrical component manufacturers and consumers.
The two most common NEMA standard connectors are the 1-15P and the 5-15; these are plugs with a body typically made of molded rubber and prongs made from steel or brass with a zinc, tin, or nickel coating. The 5-15 is used typically for general electrical devices and light-weight power loads. These are found broadly in homes, commercial, and office applications.
Other NEMA connectors carry different variations on these two common plugs, with more or differently placed prongs and increasing voltage capacities. The twist-locking L series and most other connector types are used for industrial purposes, and the types of connectors coincide with various types of use and voltage. For example, some types of locking connectors are used in boats, where there is movement and it is important that power connection not be lost or exposed where water damage could cause a short. The twist-lock cannot be pulled out of its outlet unless it is twisted open.
Devices approved by NEMA are typically engineered to be one wire or two wire devices depending on whether or not a device is polarized or grounded.
Different considerations to keep in mind when purchasing electrical components include the intended use of the power supply cord, plug or connectors, the intended energy load and transfer that will be required and the device for which it is needed.
As NEMA components are the standard for the US, other power cords and connectors will be required if there is to be any travel or exposure to an international power source. Plug adapters and international power cords are widely available, but are not always required to meet NEMA standards and therefore it will still be important to consider individual manufacturing and material quality.
Increased safety features and requirements are another benefit of having NEMA manufactured products available, and this is an important element missing from appliances that do not adhere to NEMA standards. Safety features on many NEMA parts include tamper resistant receptacles to reduce electrical shock, and grounding capabilities, especially in plugs which are intended for use in potentially wet areas such as out of doors, kitchens or basements in which a grounding capability will cut off the flow of electricity.