Spacing Between PCB Pad and HEATSINK

[SS1_Raptor]

hello friends

i have a capacitor charged with 812 V DC

in under this capacitor have a heatsink
how mush i have to Spacing Between PCB PAD and heatsink ?

Humidity max 70%
Temperature max 80 degrees

An image similar to what I need


Thanks a lot,

 

[barry]

I've seen the breakdown voltage of air listed as 1.1KV/mm; and as 30KV/cm. Not sure where those come from, and they're quite different. There's also Paschen's Law which establishes the minimum arc distance vs pressure. You also have to consider the pad geometry-you don't want a sharp point. Unless space is really critical, I'd use the 30KV/cm number, and then add some margin. Or an insulator.
https://en.wikipedia.org/wiki/Electrical_breakdown

 

[BigBoss]

In order to prevent from electrical arcs , I'd recommend yo to use a adhesive insulator between heat-sink and capacitor pads.

 

[FvM]

Is the DC bus grounded (isolated secondary circuit) or mains connected? In the latter case, you have to account for mains common mode surges. Required clearance (distance in air) for 800V secondary circuit is about 1.6 mm.
For mains connected circuit, the clearance varies depending on maximal voltage to neutral and overvoltage category.