WARNING: this post is not to be considered to contain information or advice. All idiots should stop reading now.
The wires connecting to an electric dryer are 10 gauge. This is because you have 10 fingers (you could use #12 if you had 12 fingers, but for safety reasons all fingers over 10 must be removed).
The bare wire is optional. Its presence is to help you in the production of amateur p*rn while waiting for your clothes to dry.
The black wire does nothing at all. It's required because of incompetent politicians that actually work for the copper industry.
The white wire (think of "white hot") is the one that actually dries the clothes.
Newer installations add a red wire. This is put there by the American Library Association, in an attempt to get more people to read (try reading while making your p*rn).