My customer is planning to add varnish to the component by coating. Question if the pollution degree (PD) decreases from 2 to 1 by doing this?
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I believe the isolation team might be in a better position to answer this question, but I would think such a coating would go the other direction, moving the rating from 2 to 3. Have a look at this link: https://www.ni.com/en-us/innovations/white-papers/06/pollution-degree-rating-for-electrical-equipment.html
As you begin with, Pollution degree 2 is the correct assessment for the TMCS1100 family, as the TMCS family fulfills the IEC 60950 standard (the TMCS is built to IEC 62368-1 in our data sheet, which is a newer standard that combines IEC 60950-1 for electrical equipment and IEC 60065 for audio and video equipment.)
I would think addition of a substance such as varnish would classify the device under "industrial and farming," which is category 3, since this documentation shows category 4 is defined as "pollution [that] generates persistent conductivity caused by conductive dust, rain, or snow." It could also potentially be classified as an "encapsulating mold," and if it does that, then yes, the degree may be increased to 1. It really comes down to whether or not the varnish in question is classified as a mold, or a pollutant.
I don't believe varnish would cause permanent conductivity, so category 3 would be my assessment. You might check in with the isolation team, who could give a more thorough assessment.