Clearance from PCB to earthed enclosure

[cupoftea]

Hi,
Supposing you have a 24V, 20W, 90-265 , isolated Flyback on a PCB whose edges are enclosed right up against an earthed metal enclosure.
What distance to the edge of the PCB is the primary side copper allowed to go to?
Is there any trick (to reduce distance) like having kapton tape simply stuck to the enclosure where the PCB edges touch up against it?

Also, i assume the isolated secondary side copper has just <1mm clearance requirement from the earthed enclosure, since its isolated?

 

[wwfeldman]

air is good to 30,000 V/cm or 3000 V/mm, (which assumes clean dry air at STP)

i suggest you leave at least a 2 mm space between the edge of the board and the metal enclosure
more is better

first, the tolerances may lead to the board not fitting inside the box
second, any dirt and humidity may allow a track through the dirt to the box, completly negating the insulating quality of air

 

[andre_luis]

i assume the isolated secondary side copper has just <1mm clearance requirement from the earthed enclosure

I don't think we can apply such accuracy in the PCB cutting process during manufacture, particularly if divided by panelization.

 

[cupoftea]

thanks, but 1mm is OK , surely?