The methods of measuring creepage distances and clearances are indicated in the following Examples 1 to 11. These cases do not differentiate between gaps and grooves or between types of insulation.The following assumptions are made:-any recess is assumed to be bridged with an insulating link having a length equal to the specified width X and being placed in the most unfavourable position;-where the distance across a groove is equal to or larger than the specified width X, the creepage distance is measured along the contours of the groove;-creepage distances and clearances measured between parts which can assume different positions in relation to each other, are measured when these parts are in their most unfavourable position.