High Voltage Nodes creep-age and clearance standards for electronics?
To avoid creapage currents spacing alone is not good enough. Many board houses can do slot cuts as narrow as 31 mils, or .031". I worked at a surge suppression plant where most all boards had 120 VAC to 600 VAC at one end, and 5 VDC for diagnostics.

The key is to slot-cut under opto-couplers and between phases, next to the lead with the high voltage. This way, with a conformal coating of polyurethane added, the high voltage is 'trapped' at its point of entry.

This includes resistors and capacitors that tap into the high voltage for various reasons. Most slot cuts are 1 cm or 3/8 inch long at most. Yes, they do charge for slot cuts, but it is worth it because if a 'mains' feed to the board starts to arc from creapage, it will quickly turn into a plasma ball that will burn a hole in steel in 1/4 of a second.

If soot leaks to other phases on a split-phase or 3 phase board it quickly becomes a bomb.

There were no standards for this, so the chief engineer played it safe and isolated any high-voltage with slot cuts, even some 'L' shaped cuts. Conformal coating was part of our standard procedures once a board passed testing.