  A scenario for the formation of symmetry protected non-Fermi-liquid (NFL)
Kondo effect (KE) with spin variable enumerating Kondo channels is suggested
and worked out. In doubly occupied symmetric triple quantum dot within parallel
geometry, the NFL low-energy regime arises provided the device possesses both
source-drain and left-right parity. Kondo screening follows a multistage
renormalization group mechanism: reduction of the energy scale is accompanied
by the change of the relevant symmetry group from SO(8) to SO(5). At low
energy, three phases compete: 1) under-screening spin triplet (conventional)
KE; 2) spin singlet potential scattering; 3) NFL phase where the roles of spin
and orbital degrees of freedom are swapped.
