Tap: a conductor with overcurrent protection ahead of its source of supply that is > ampacity of tap conductor (article 240)
minimum tap conductor ampacity is based on conductor length
see 240.21(B) for addtl. installation requirements and allowances for feeder taps
Looking at example of tap that are 10 feet or less
>= imax X 1.25 + feeder OCPD X .10
AND
>= OCPD rating at load end of tap
Looking at example of tap that are MORE than 10 feet and LESS than 25 feet
>=( imax X 1.25 + feeder OCPD ) X .33
AND
>= OCPD rating at load end of tap