European distribution system operators (DSOs) should meet EN 50160 standard requirements on the whole network. With the development of distributed energy resources (DER), DSOs need to have a better insight of their low voltage (LV) networks. In this paper, we study the joint impact of external conditions (cable temperature, the ground resistivity and the ground resistances) on the voltage profile of three LV networks in four cases. The results show that some voltage problems cannot be seen by using only usual values of those external conditions. By considering the values that are closer to the real conditions, the voltage analysis will be more accurate and in some cases, additional problems can be detected. To be sure that the EN 50160 standard is met, a global study of LV networks including the external conditions should be done.