Does wire diameter affect the electricity bill?
You are REQUIRED by code to use specific wire sizes for specific loads and in no case can you use a wire that is rated for less than 125% of a continuous load. So if you follow the law, your wire heating is minimal. If you increase the wire size to be larger than necessary, it will technically reduce the losses, but at a much lower rate of increase in benefit so there is almost never a return on that investment. The energy savings may be only a few dollars per year, whereas the cost of the larger wire for an entire house may result in hundreds of dollars in increased cost. You would not likely live long enough for the energy savings to pay for itself.