This paper deals with the magnetic field generated by medium‐voltage/low‐voltage substations. Particularly, the paper focuses on the computation of the distance of compliance that is defined as the minimum distance from a field source for having field levels lower than a given threshold. In the first part of the paper, some 3D integral models are proposed to compute the magnetic field generated by each field source present in substations (transformers, cables, etc...). In the second part of the paper, we make use of these integral models to develop a simplified analytical approach for the computation of an approximate distance of compliance, that is, a conservative distance that includes the previously mentioned distance of compliance. The advantage of this approach is that it is composed of simple equations that are very easy to be implemented without losing the tridimensionality of the problem. Copyright © 2013 John Wiley & Sons, Ltd.