In America, the National Electrical Manufacturers Association (NEMA) establishes many of the guidelines for electrical components. This includes electrical outlets, or receptacles, all of which must meet certain standards for safety and compatibility.
The two kinds of receptacles are Type A and Type B, or NEMA 1 and NEMA 5, respectively. Type A has two parallel slots for the plug blades; Type B has these and an additional ground slot, fitting a circular ground pin. All Type B and some Type A--"new" Type A--have two sizes for the slots, with the "taller" one used for the neutral.
Type A and Type B are rated for 125 volts alternating current. A North American device intended for a different voltage will not fit into either receptacle type. Both types are rated for 15 amps.
Plugs intended for "old" Type A will fit any Type A or Type B receptacles. Plugs intended for "new" Type A will fit all "new" Type A and all Type B receptacles but not "old" Type A receptacles. Plugs intended for Type B receptacles will fit only Type B.
Places of use
Among others, these countries also use both types of receptacles: Antigua, the Bahamas, Bermuda, Brazil, Canada, Colombia, Costa Rica and Cuba.