...and also be sure to keep a good eye on your Variac output voltage. It is a good idea to use a multimeter, because line voltages can vary quite a bit. This is especially true during the Summer months when the power company is trying to manage peak hour power demands.
Also be sure to check your variac dial scale when reading voltage output to get an idea of where you get 120V output with 120V input. One of the two variacs that I just purchased this month was manufactured in Japan. It is a very nice 5 amp variac, however it is rated at 130V maximum output with 100V input. So when I crank the variac dial to the maximum of 130V, I am seeing an output of 165V!. Just like Dirty Harry said, "A man has gotta know his limitations"
Good Luck