Internal wiring shall be either so rigid and so fixed or so insulated that, in normal use, creepage distances and clearances cannot be reduced below the values specified in 28.1. The insulation, if any, shall be such that it cannot be damaged in normal use.Compliance is checked by inspection, by measurement, and by manual test.For insulated internal wiring, it is checked that either their insulation is electrically equivalent to the insulation of the cords complying with IEC 60227 or IEC 60245, or it complies with the following electric strength test.A voltage of 2 000 V is applied for 15 min between the conductor and metal foil wrapped around the insulation. There shall be no breakdown.When sleeving is used as supplementary insulation on internal wiring, it shall be retained in position by positive means. A sleeve is considered to be fixed by positive means if it can only be removed by breaking or cutting, or if it is clamped at both ends.Compliance is checked by inspection and by manual test.