  We investigate separability and entanglement of mixed states in ${\cal
C}^2\otimes{\cal C}^2\otimes{\cal C}^N$ three party quantum systems. We show
that all states with positive partial transposes that have rank $\le N$ are
separable. For the 3 qubit case (N=2) we prove that all states $\rho$ that have
positive partial transposes and rank 3 are separable. We provide also
constructive separability checks for the states $\rho$ that have the sum of the
rank of $\rho$ and the ranks of partial transposes with respect to all
subsystems smaller than 15N-1.
