In just under 0.18 seconds, Google reported http://www.cadsymbols.com/ this link amongst others. You might want to try something like this first. As to American design, that's pretty nebulous. You'll need to be more specific. Design of what - cars, stereos, lasers, houses ???
Years ago (about 12) there used to be a CAD system called Orcad that specialised in electrical symbology. I'm not sure if it was free but if it cost anything, it would only have been a few bucks!
Thinking back, by modern day standards it was crap but it did do the job. Where it would/may let you down would be in the presentation. Having said that, they have probably got version 2008 on the go and charge big bucks. Check the web!
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"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools!" Douglas Adams 1952-2001. E&OE!