Filter’s current ratings are specified at maximum ambient temperature surrounding the filter when operating at full load. For FN2000 series this temperature must not exceed 40°C for the rated current to remain valid. However, it is possible to de-rate filters to be used at higher ambient temperatures. For example FN2030-16-06 rated 16A @ 40°C can be de-rated to 13A @ 60°C. To calculate this the engineer requires the following information from the datasheet and the shown formula: θN is Rated Ambient Temperature (typically 40°C), θact is Actual Ambient Temperature required (60°C in the example shown), θmax is Maximum Operating Temperature (typically 100°C), IN is Rated Current (16A in the example shown), and I will be de-rated Current (calculated 13A in the example shown).