First-principles calculations are used to investigate the partial dislocations in 4H-SiC. We show that the stability of the dislocation cores and the Peierls barriers of the first kind are charge-state dependent. In intrinsic bulk the partials are stable in the neutral asymmetric reconstructions. These reconstructions have no deep states and are characterized by high Peierls barriers. In strongly doped regime the symmetric reconstructions can become more stable. These reconstructions are always electrically active with a half filled band across the band gap. In particular the symmetric reconstructions of the 30° partial have a lower Peierls barriers than the respective asymmetric ones and could be the cause of the 1.8 eV electroluminescence peak observed under carrier injection conditions.