Both. However its really 14/2 and 12/2 Normally we do not count the uninsulated ground wire in the numbers. However they do use three wires in three way switches or where they want to run two circuits to a location and use only one ground back. Not sure if they still use this practice or not, but years ago this was common occurrence in an effort to save money on wire.
Normally 14 wire is used for outlets or lamps, with the exception of areas such as baths laundries and kitchens where they want to use a 20 amp breaker then they use 12 wire. Or where they are installing very large fixtures which require a larger breaker because of the load that they require.
Kitchens require two 20 amp circuits for small appliances, And if you use a three wire where there are two circuits with one ground wire going back to panel, The breakers for the two circuits must be tied on handle so both are turned off at same time should you need to service one of the circuits or if a short occurs.
Thank you Woodbridge, I didn't find this in my Code Check book, I appreciate your answer.
Kitchens Outlets, Bathroom Outlets, and Dining Outlets must be 12/2 or 20 amps. All other lighting and outlets are generally installed with 14/2 15 amps. 14/3 is only used to add 3 way switches or ceiling fans.
Here is an add-on question. Are you ever allowed to "mix" the 12 gauge with the 14 gauge..? if so, is there a difference in the order it can be used?
Its my understanding that you can mix, but you must be sure that the breaker is sized for the smaller size wire. It is not really something that you would ever see done in new construction, but found quite a lot in remodels. And I would suggest that it not be done, but there is no harm by using a bigger wire then what the breaker is designed to protect.
you can use 12 where 14 is needed but not the other way around. It is always okay to upsize the wire not downsize
The inspectors in Atlanta and Fulton county do not allow any downsizing of wire..if it's a 20 amp circuit with 12/2, it's12/2 to the dead end device.
As a general rule, all outlet circuits should be 20amp and lighting circuits should be 15 amp.