I have questions during reading IPC-2221 6.3 Electrical Clearance(Table 6-1 Electrical Conductor Spacing):

1. Why the Electrical Conductor Spacing of B3(External Conductor, uncoated, over 3050m)is larger than B2(External Conductor, uncoated, sea level to 3050m) under the same voltage?

2. Why define 3050m as the interfacial one?

3. Can help to explain why there's only difference spacing under 251-300 voltage between A5(External Conductors, with conformal coating over assembly(any elevation) )and A7(External Component lead termination, with conformal coating(any elevation) ) , while the same under the other voltage groups?

Anybody can give me some direction?

Thanks with best regards,
Zhangshoukai

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