Hullguy is an licensed electrician, so if he wanders past this thread he might be able to shed some light on the subject. In the interim, here\'s a good FAQ I found on google that offers some guidelines. It includes a wire size chart about half way down the page. The chart gives the following values: 14ga for 15A, 12ga for 20A, 10ga for 30A, 8ga for 40A, and 6ga for 65A. It also recommends increasing wire size for runs longer than 100 feet. Based on that, a 20A circuit should use 12ga wire. If it's long run, it should use 10ga.

Circuit breakers are interchangeable because it makes electrical panels significantly less expensive. The same space in the panel can hold a 15A breaker or a 20A breaker, and two spaces can be used for larger breakers. This interchangeability should not be construed as suggesting that you can swap out different sized breakers any time you want. The installer must still make sure that the wiring used for each circuit is properly sized for the length of run and the load.

Nutone can of course sell their units, but when they say "20A circuit" they mean the entire circuit, including wiring. If you don't have a 20A circuit available, they assume you will either run one or pay to have one run. If you don't run one, it would be better to keep the 15A breaker - it would be more likely to be tripped under certain circumstances, but it would also reduce the risk of overheating that 14ga conductor (thereby reducing the risk of fire). Outlaw recommends a 20A circuit for the 770 because its power supply is capable of using 20A of power if it is available and there is a call for it. Most 770's are connected to 15A circuits and typically share that circuit with other devices, but they still work because the 770 does not "need" that full 20A under normal circumstances. If you had a system where you were trying to wring a full 1400W of power out of the 770 at one time, you would need to either put in a dedicated 20A circuit or get used to resetting the 15A breaker. Of course, that would also require some severely loud listening levels, some very unusual source material, and probably some pretty inefficient speakers.