The paper deals with the issue of choosing external insulation (for transmission lines and external switchgear) under conditions of significant snow and/or ice impact. The parameters of snow and ice that influence the occurrence of jumps on the external insulation of HV transmission lines and apparatus in switchgear were analyzed. Methods of testing insulation under the influence of snow and ice in high-voltage test laboratories equipped with special ice chambers are presented. Recommendations for methods of testing and designing (execution) of external insulation are presented, as well as the selection of tolerable external insulation voltages in conditions of increased influence of snow and ice.