When my son and I were replacing a few electric outlets in the house yesterday, after another old one in his room failed, in the original part of the house, was burning out, we discovered that the two we were replacing in the back of the house,just so we wouldn't need adapters for the two prong outlets, which was built on by my dad in the late 1960's, that he wired everything backward. Son's room is in the original part of the house, built in 1963. Back part built by dad about 6 years later. Black and White wires in the back of the house were reverse. Guess dad didn't know the "standard" when he wired the add on.