Mandatory versus Custom-Driven Requirements
OEMs have seen a strong correlation between field reliability and surge survivability. The mandatory EN level is just 1 kV, but as we can see from Fig. 11.2 (sourced from IEEE 587), we can get hit by one surge of 5 kV once a year, and 3 to 4 kV thrice a year (in the United States at least). That can be a lot of field returns. So there is an increasing demand for passing higher and higher surge ratings. Several issues arise in deciding the best target to chase in an economical manner.