Can anyone explain on what basis Vsiov has been calculated using the equation Vsiov=1000x 0.9/1.1. I need to use an MOV from EPCOS S14 series to satisfy surge conditions as per IEC 61000-4-5. I have attached a snapshot of the calculation.

 

I have been looking into the same as you for my project. As far as I can see the MOV should be approx 20% above supply voltage. I think I have settled on 300V. I believe the air discharge test is now 8kv (lightening strike protection) but may be for your application it is 4kv.

The power supply I selected recommended the S14 range as well.

 

Yes but how did the 820V calculation come out. I searched for it a lot but I am not able to understand it.