The goal of the IEC60664-1 is to provide guidance on designing insulation for products that have a connection to mains supply.

However some cases are not covered by this calculator:

- For frequencies higher than 30kHz, the dielectric performances are degraded. IEC60664-4 covers those cases
- When using a conformal coating or a potting in order to protect for pollution, if all conditions specified by IEC60664-3 are met, the clearance and creepage distances can be reduced. Soldermask is usually not considered as a conformal coating.
- Insulations trough liquids, compressed air or gases other than air are not in the scope of IEC60664