Internal wiring shall be either so rigid and so fixed or insulated that creepage distances and clearances cannot be reduced below the values specified in 28.1.Compliance is checked by inspection and by the tests of 28.1.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.