We undertake a simultaneous partial wave analysis of proton-proton and neutron-proton scattering data below the pion production threshold up to laboratory energies of 350 MeV. We represent the interaction as a sum of delta shells in configuration space below 3 fm and a charge dependent one pion exchange potential above 3 fm together with electromagnetic effects. We obtain a chi square value of 2813, for pp, and 3985, for nn, with a total of 2747 and 3691 pp and nn data, respectively, obtained till 2013 and a total number of 46 fitting parameters yielding a chi square value by degree of freedom of chi(2)/d.o.f = 1.06. Special attention is payed to estimate the errors of the phenomenological interaction as well as the derived effects on the phase shifts and scattering amplitudes.