Clearance and Creepage Distances
(in accordance with EN 60664-1:2007 and VDE 0110-1)
Clearance is the shortest distance in air between two conductive parts. Clearance shall be dimensioned to withstand the required impulse withstand voltage, in accordance to table "Clearances to withstand transient overvoltages". For equipment directly connected to the low-voltage mains the required impulse withstand voltage is the rated impulse voltage, can be found in the table titled "Rated impulse voltage for equipment...," according to application.
Larger clearances may be required due to mechanical influences such as vibration or applied forces.
Inasmuch as the values indicated in the aforementioned tables are applicable up to 2.000 meters above sea level, clearance for greater heights must be calculated using the multiplication factors in the "Altitude correction factors" table.
Creepage distance means the shortest distance along the surface of a solid insulating material between two conductive parts. The values of table "Creepage distances to avoid failure due to tracking" are based upon existing data and are suitable for the majority of applications.
The basis for the determination of a creepage distance is the long-term r.m.s. value of the voltage existing across it. This voltage is the working voltage, the rated insulation voltage or the rated voltage.
The influence of the degrees of pollution in the micro-envitonment on the dimensioning of creepage distances is taken into account in table "Creepage distances to avoid failure due to tracking". To keep in mind is also that in the same equipment, different micro-environment conditions can exist.
A creepage distance cannot be less than the associated clearance so that the shortest creepage distance possible is equal to the required clearance. However, there is no physical relationship, other than this dimensional limitation, between the minimum clearance in air and the minimum acceptable creepage distance.
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