We were trying to I.D. a circuit and I intentionally tripped it with my handy "U" shaped piece of #12.
Take a look here: http://electrical-contractor.net/ubb/Forum16/HTML/000239.html
You might want to rethink that practice. A lot of buildings today have a lot of short-circuit current available even at a common recept. You may find yourself on the wrong end of a very bad arc fault.
The buildings I work in (cinemas) are a prime example. Most of them have series-rated systems to try to limit fault current let-through.
And let's not forget the possibilty of encountering the famous FPE "no-trip" breaker!!
Work safe everybody!!