A table is in 3NF when it is in 2NF and contains no transitive dependencies. Given that defintion of 3NF,the Boyce-codd normal from (BCNF) is merely a special 3nF case in which all determinant keys are candidate keys. when a table has only a single candidate key, a 3NF table is automatically in BCNF.
A table that is not in 3NF may be split into new tables until all of the tables meet the 3NF requirments.