There are two basic classifications of NEMA device: straight-blade plug and twist lock plugs
. The straight-blade 5–15 and 5–20 power cordsets are found in countries using the NEMA standards and are intended for supplying lighter-duty, general-purpose electrical devices. Twist lock plugs types are used for heavy industrial and commercial equipment where increased protection against accidental disconnection is required. Numbers prefixed by L are curved-blade, twist-locking plug; others are straight blade and non-locking power cordsets
The numeral preceding the hyphen in NEMA nomenclature indicates the configuration for the power cordsets, i.e., the number of poles, wires, voltage, single phase, three-phase or twist lock plugs
. A grounding device will be described as two-pole, three-wire; or four-pole, five-wire; etc. A non-grounding device will be two-pole, two wire; or three-pole, three-wire; etc.
The numeral following the hyphen is the power cordsets
rating in amperes. The number is followed by the letter R indicating a receptacle (female connector) or the letter P indicating a plug (male connector). If there is an L in front of the first number, this indicates a twist lock plugs.
For example, the 5–15R is the common 125 V two-pole, three-wire receptacle. The L5–15R, while sharing the same rating, is a twist lock plug design which is not physically compatible with a straight-blade 5–15 power cordsets. The 5–30 power cordset has the same two-pole, three-wire configuration and 125 V rating, but is rated 30 A.