This Supplement 1 to DIN EN 60664-1 (VDE 0110-1) provides a guideline regarding the insulation coordination according to the DIN EN 60664 standard series for the technical committees and manufacturers. The supplement contains general information on the design of clearances in air, creepage distances and solid insulation of equipment. It aims at promoting the understanding and the application of the DIN EN 60664 (VDE 0110) standard series by the technical committees and manufacturers. The insulation coordination for equipment is based on the determination of the minimum dimensions for clearances in air, creepage distances and solid insulation in order to allow for safe use of equipment during its life by taking into account the environmental conditions to be expected. The significant aspects to be considered are the following: a) the nominal voltage of the distribution system or the rated insulation voltage; b) overvoltage category of the equipment; c) every type of overvoltage; d) the frequency of voltage; e) the characteristics of the solid insulation; f) the pollution degree and the degree of moisture. Other stresses such as temperature rise, vibration, shock, radiation, etcetera, may influence the behaviour of the solid insulation in application practices. When specifying the test conditions for equipment applied under the corresponding conditions, technical committees and manufacturers should take into account the hazards associated with these stresses. The responsible committee is K 123 "Isolationskoordination für Niederspannungs-Betriebsmittel" ("Insulation coordination for low-voltage equipment") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.