NEMA Nomenclature
There are two basic classifications of NEMA device: straight-blade and locking. The twist-locking type is preferred in many industrial environments, while the residential and commercial environment is home to straight-blade devices. (Of course, the straight-blade 5-15 and 5-20 are found nearly everywhere.) Numbers prefixed by L are curved-blade, twist-locking connectors, others are straight blade non-locking.
The numeral preceding the hyphen in NEMA nomenclature indicates the configuration type, i.e. number of poles, number of wires, voltage, and whether single- or three-phase. A grounding type of 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 rating of the device in amperes. The number is followed by the letter R to indicate a receptacle or the letter P to indicate a plug.
As an example, the 5-15R is the common 125V two-pole, three-wire receptacle. The L5-15R, while sharing the same rating, is a locking design which is not physically compatible with the straight-blade 5-15 design. The 5-30 has the same two-pole, three-wire configuration and 125V rating, but is rated 30 amperes.
Although there are several non-grounding device types in the NEMA standards, only a few of them are in widespread use today. These are the two-pole 1-15, still in use in millions of buildings built before 1965, and the three-pole 10-30 and 10-50.
