14 gauge or 14 AWG copper wire can safely handle up to 15 amps of electricity and a 14 AWG copper wire needs to be put on a 15 amp circuit breaker.
For 20 amps you need 12 gauge or 12 AWG copper wire and have it on a 20 AMP circuit breaker.
14 AWG is most commonly used as wiring for lighting circuits but in some older homes and older mobile homes I've seen 14 AWG copper wire used as all the electrical circuits.
However new homes built today use 12 gauge copper wire for the electrical circuits and sometimes for the lighting circuits as well.