This is from a google search.
Marv
The general rule of thumb for picking wiring size is · 14-gauge wire is rated for currents up to 15 amps. Circuits in many homes, especially cost-conscious tract homes, use 14-gauge wiring in most of the house except the kitchen; even in the garage. This is a distinct disadvantage nowadays due to hair dryers in bathrooms, computers and other equipment in bedroom/home offices, etc. Avoid 14-gauge wiring in any new home if you are building.
· 12-gauge wire for currents up to 20 amps. But a 20-amp breaker must not be loaded above 16 amps of continuous current draw. This is adequate for most home shops, provided your bigger tools operate on 240-volt power, and you don't have multiple tools going at the same time. · 10-gauge wire for up to 30 amps, or 40 amps if you are running intermittently loaded motors such as on a table saw or jointer that is not being used for big production jobs or jobs where you are doing a lot of continuous cutting. With intermittent loads, you can use 40-amp breakers, because a 40-amp breaker should not be loaded at more than 32 amps continuous. Just be aware that you will have more heating in the wire, so it be as open to ventilation as possible. It shouldn't be buried under the insulation in an attic, for example, between the breaker panel and the plug in the wall. 10-gauge wire is rarely used on 120-volt circuits.