The National Electrical Manufacturers Association provides a chart on the proper arrangement of NEMA configurations. The first order of business is distinguishing between connectors, receptacles, inlets and plugs. The male connectors are to be latched into the load, whereas the female connectors connect to a source of electrical power.
NEMA uses code numbers for some devices, which denote several properties. One of the numbers indicates whether the connector is a receptacle or a plug, and thus whether it connects to a load or a power source. A letter comprises one of the figures and refers to the voltage and amperage rating, and the last denotes whether a locking mechanism is present. If there is no locking mechanism, this letter is absent.