The temperature and electric field dependence of the current density in hydrogenated amorphous carbon and carbon nitride sandwich devices show a T-1/4 dependence of the ohmic conductivity sigma = sigma(00) - exp[-(T-0/T)(1/4)] characteristic of 3D hopping, a linear correlation between the apparent Lnsigma(00)(F) and T-0(F) values, and a F/T-3/2 scaling of sigma(F, T). The F-2 dependence of Lnsigma(F, T) at intermediate fields, provides similar values of the decay length gamma(-1) of localized 71 state wavefunctions in a-CNx:H (2.4 nm) and a-C:H (2.8 nm) films. The larger conductivity in nitrogen-rich alloys is attributed to a combined effect of N-induced increase in the pi-state density and ordering of the sp(2) phase.