Name: Dennis G.
Date: June 2004
How long have polarized outlets/plugs been in use in the U.S.?
I regret that I do not know. This is a history of technology question and
the answer might be found on the Internet.
The two wire (nongrounded) receptacle is found only in older houses built before the
mid-1960's in the United States. I hope that this is sufficient.
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Update: June 2012