This type is mainly used in USA,Canada,Mexico and Japan.The plug has two parallel blades. Early versions were not polarized, but almost all plugs are polarized today via a taller neutral blade on the plug and corresponding plug on the receptacle.

Ungrounded NEMA-1 outlets are not permitted in new building construction in the United States and Canada, but can still be commonly found in older construction. Allowed replacement of NEMA-1 receptacles varies by local code.