The clearances and creepage distances for open and enclosed indoor-type air-insulated busbars, as suggested by BS 159, are given in Tables 1 and 2 respectively. These values are considered for an altitude of up to 2000 m for LT and 1000 m for HT systems. For higher altitudes to achieve the same level of dielectric strength, the values of clearances and creepage distances, as given in Tables 1 and 2, may be increased by at least 1% for every 100 m rise in altitude. 
