for one motor on the branch... size branch circuit @ 125% of motor full load amps as listed in NEC 430.150. 15HP @ 208V 3ph ==> 46.2 amps 125% ==> 57.8 amps select wire (after derations) for 57.8 amps
the design letter "B" is used for selecting overload protection PF=80% is typical for induction motors but has no bearing on wire size. NEC table 430.150 has PF allowances "built-in" for induction motors.
hope this helps.
Re: NEC Article 430#81252 08/08/0203:26 PM08/08/0203:26 PM