I am looking for information on the basis by which the generic conductor spacings were determined in IPC and other standards for dielectric breakdown. I understand that many factors effect the spacing required voltage, frequency, temperature, aging etc.

For these factors what margin of safety was applied?
How were they determined I assume by test and analytical techniques combined? I would like to repeat this process since our dieelectric is not a common one.
Our dielectric is Teflon (500V/mil rated according to Dupont). The application worstcase is 120V beteen adjacent conductors, would 4 mil be accpetable a factor of 4 and change margin?

Thanks in advance to those who respond.

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