2G HTS wires produced with the MOD/RABiTS process with NiW substrates have weak magnetism and therefore extra losses in a substrate. The goal of this paper is to find out the model that could describe losses just in a substrate only. Two and three dimensional numerical electromagnetic field analysis has been developed for two-layer cables made of 2G HTS conductors with magnetic substrates. Two arrangements were used for the 2G conductors between the inner and outer layers: tape-on-tape and tape-on-gap. Comparisons of calculations with measured ac loss are presented.