The kaonic cluster ppK^- p p K − is described by isospin-dependent N{\bar K} N K ‾ potentials with significant difference between singlet and triplet components. The quasi-bound state energy of the system is calculated based on the configuration space Faddeev equations within isospin and averaged potential models. The isospin averaging of N{\bar K} N K ‾ potentials is used to simplify the isospin model to isospinless one. We show that three-body bound state energy E_{3} E 3 has a lower bound within the isospin formalism due to relation \left\vert E_{3}(V_{NN}=0)\right\vert<2\left\vert E_{2}\right\vert | E 3 ( V N N = 0 ) | < 2 | E 2 | , where E_{2} E 2 is the binding energy of isospin singlet state of the N{\bar K} N K ‾ subsystem. The averaged potential model demonstrates opposite relation between |E_{2}| | E 2 | and |E_{3}(V_{NN}=0)| | E 3 ( V N N = 0 ) | .