The results of investigations of the dissociation of a $^{14}$N nucleus of momentum 2.86~A~GeV/c in photo-emulsion are presented. The main characteristics of these reactions, that is the cross sections for various fragmentation channels, are given. The fragmentation was analyzed by means of an invariant approach. The momentum and correlation characteristics of $alpha$ particles for the $^{14}$N$to3alpha$+X channel in the laboratory system and the rest systems of 3$alpha$ particles were considered. The results obtained for the $^{14}$N nucleus are compared with similar data for the $^{12}$C and $^{16}$O nuclei.